[PATCH V2 0/4] xen: Add support of extended regions (safe ranges) on Arm

[PATCH V2 0/4] xen: Add support of extended regions (safe ranges) on Arm

[Oleksandr Tyshchenko]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

You can find the RFC patch series at [1].

The corresponding Xen support (for both Dom0 and DomU) is already committed and
is available in mainline Xen since the following commit:
57f87857dc2de452a796d6bad4f476510efd2aba libxl/arm: Add handling of extended regions for DomU

The extended region (safe range) is a region of guest physical address space
which is unused and could be safely used to create grant/foreign mappings instead
of ballooning out real RAM pages to obtain a physical address space for creating
these mappings (which simply results in wasting domain memory and shattering super
pages in P2M table).

The problem is that we cannot follow Linux advise which memory ranges are unused
on Arm as there might be some identity mappings in P2M table (stage 2) the guest is not
aware of or not all device I/O regions might be known (registered) by the time the guest
starts creating grant/foreign mappings. This is why we need some hints from the hypervisor
which knows all details in advance to be able to choose extended regions (which won't
clash with other resources).

The extended regions are chosen at the domain creation time and advertised to it via
"reg" property under hypervisor node in the guest device-tree [2]. As region 0 is reserved
for grant table space (always present), the indexes for extended regions are 1...N.
No device tree bindings update is needed, guest infers the presence of extended regions
from the number of regions in "reg" property.
    
Please note the following:
- The ACPI case is not covered for now
- patch series was created in a way to retain existing behavior on x86

The patch series is based on v5.15-rc7 and also available at [3], it was fully
tested on Arm64 and only compile tested on x86.

[1] https://lore.kernel.org/all/1627490656-1267-1-git-send-email-olekstysh@gmail.com/
    https://lore.kernel.org/all/1627490656-1267-2-git-send-email-olekstysh@gmail.com/

[2] https://xenbits.xen.org/gitweb/?p=xen.git;a=blob_plain;f=docs/misc/arm/device-tree/guest.txt;hb=refs/heads/master

[3] https://github.com/otyshchenko1/linux/commits/map_opt_ml5

Oleksandr Tyshchenko (4):
  xen/unpopulated-alloc: Drop check for virt_addr_valid() in fill_list()
  arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT
  xen/unpopulated-alloc: Add mechanism to use Xen resource
  arm/xen: Read extended regions from DT and init Xen resource

 arch/arm/xen/enlighten.c        | 144 ++++++++++++++++++++++++++++++++++++++--
 drivers/xen/Kconfig             |   2 +-
 drivers/xen/unpopulated-alloc.c |  90 +++++++++++++++++++++++--
 include/xen/xen.h               |   2 +
 4 files changed, 226 insertions(+), 12 deletions(-)

-- 
2.7.4


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH V2 2/4] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT

[Oleksandr Tyshchenko]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

Read the start address of the grant table space from DT
(region 0).

This patch mostly restores behaviour before commit 3cf4095d7446
("arm/xen: Use xen_xlate_map_ballooned_pages to setup grant table")
but trying not to break the ACPI support added after that commit.
So the patch touches DT part only and leaves the ACPI part with
xen_xlate_map_ballooned_pages().

This is a preparation for using Xen extended region feature
where unused regions of guest physical address space (provided
by the hypervisor) will be used to create grant/foreign/whatever
mappings instead of wasting real RAM pages from the domain memory
for establishing these mappings.

The immediate benefit of this change:
- Avoid superpage shattering in Xen P2M when establishing
  stage-2 mapping (GFN <-> MFN) for the grant table space
- Avoid wasting real RAM pages (reducing the amount of memory
  usuable) for mapping grant table space
- The grant table space is always mapped at the exact
  same place (region 0 is reserved for the grant table)

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
---
Changes RFC -> V2:
   - new patch
---
 arch/arm/xen/enlighten.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 7f1c106b..dea46ec 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -59,6 +59,9 @@ unsigned long xen_released_pages;
 struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
 
 static __read_mostly unsigned int xen_events_irq;
+static phys_addr_t xen_grant_frames;
+
+#define GRANT_TABLE_INDEX   0
 
 uint32_t xen_start_flags;
 EXPORT_SYMBOL(xen_start_flags);
@@ -303,6 +306,7 @@ static void __init xen_acpi_guest_init(void)
 static void __init xen_dt_guest_init(void)
 {
 	struct device_node *xen_node;
+	struct resource res;
 
 	xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
 	if (!xen_node) {
@@ -310,6 +314,12 @@ static void __init xen_dt_guest_init(void)
 		return;
 	}
 
+	if (of_address_to_resource(xen_node, GRANT_TABLE_INDEX, &res)) {
+		pr_err("Xen grant table region is not found\n");
+		return;
+	}
+	xen_grant_frames = res.start;
+
 	xen_events_irq = irq_of_parse_and_map(xen_node, 0);
 }
 
@@ -317,16 +327,20 @@ static int __init xen_guest_init(void)
 {
 	struct xen_add_to_physmap xatp;
 	struct shared_info *shared_info_page = NULL;
-	int cpu;
+	int rc, cpu;
 
 	if (!xen_domain())
 		return 0;
 
 	if (!acpi_disabled)
 		xen_acpi_guest_init();
-	else
+	else {
 		xen_dt_guest_init();
 
+		if (!xen_grant_frames)
+			return -ENODEV;
+	}
+
 	if (!xen_events_irq) {
 		pr_err("Xen event channel interrupt not found\n");
 		return -ENODEV;
@@ -370,12 +384,16 @@ static int __init xen_guest_init(void)
 	for_each_possible_cpu(cpu)
 		per_cpu(xen_vcpu_id, cpu) = cpu;
 
-	xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
-	if (xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
-					  &xen_auto_xlat_grant_frames.vaddr,
-					  xen_auto_xlat_grant_frames.count)) {
+	if (!acpi_disabled) {
+		xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
+		rc = xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
+										   &xen_auto_xlat_grant_frames.vaddr,
+										   xen_auto_xlat_grant_frames.count);
+	} else
+		rc = gnttab_setup_auto_xlat_frames(xen_grant_frames);
+	if (rc) {
 		free_percpu(xen_vcpu_info);
-		return -ENOMEM;
+		return rc;
 	}
 	gnttab_init();
 
-- 
2.7.4


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH V2 4/4] arm/xen: Read extended regions from DT and init Xen resource

[Oleksandr Tyshchenko]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

This patch implements arch_xen_unpopulated_init() on Arm where
the extended regions (if any) are gathered from DT and inserted
into passed Xen resource to be used as unused address space
for Xen scratch pages by unpopulated-alloc code.

The extended region (safe range) is a region of guest physical
address space which is unused and could be safely used to create
grant/foreign mappings instead of wasting real RAM pages from
the domain memory for establishing these mappings.

The extended regions are chosen by the hypervisor at the domain
creation time and advertised to it via "reg" property under
hypervisor node in the guest device-tree. As region 0 is reserved
for grant table space (always present), the indexes for extended
regions are 1...N.

If arch_xen_unpopulated_init() fails for some reason the default
behaviour will be restored (allocate xenballooned pages).

This patch also removes XEN_UNPOPULATED_ALLOC dependency on x86.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
---
Changes RFC -> V2:
   - new patch, instead of
    "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide unallocated space"
---
 arch/arm/xen/enlighten.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++
 drivers/xen/Kconfig      |   2 +-
 2 files changed, 113 insertions(+), 1 deletion(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index dea46ec..1a1e0d3 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -62,6 +62,7 @@ static __read_mostly unsigned int xen_events_irq;
 static phys_addr_t xen_grant_frames;
 
 #define GRANT_TABLE_INDEX   0
+#define EXT_REGION_INDEX    1
 
 uint32_t xen_start_flags;
 EXPORT_SYMBOL(xen_start_flags);
@@ -303,6 +304,117 @@ static void __init xen_acpi_guest_init(void)
 #endif
 }
 
+#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
+int arch_xen_unpopulated_init(struct resource *res)
+{
+	struct device_node *np;
+	struct resource *regs, *tmp_res;
+	uint64_t min_gpaddr = -1, max_gpaddr = 0;
+	unsigned int i, nr_reg = 0;
+	struct range mhp_range;
+	int rc;
+
+	if (!xen_domain())
+		return -ENODEV;
+
+	np = of_find_compatible_node(NULL, NULL, "xen,xen");
+	if (WARN_ON(!np))
+		return -ENODEV;
+
+	/* Skip region 0 which is reserved for grant table space */
+	while (of_get_address(np, nr_reg + EXT_REGION_INDEX, NULL, NULL))
+		nr_reg++;
+
+	if (!nr_reg) {
+		pr_err("No extended regions are found\n");
+		return -EINVAL;
+	}
+
+	regs = kcalloc(nr_reg, sizeof(*regs), GFP_KERNEL);
+	if (!regs)
+		return -ENOMEM;
+
+	/*
+	 * Create resource from extended regions provided by the hypervisor to be
+	 * used as unused address space for Xen scratch pages.
+	 */
+	for (i = 0; i < nr_reg; i++) {
+		rc = of_address_to_resource(np, i + EXT_REGION_INDEX, &regs[i]);
+		if (rc)
+			goto err;
+
+		if (max_gpaddr < regs[i].end)
+			max_gpaddr = regs[i].end;
+		if (min_gpaddr > regs[i].start)
+			min_gpaddr = regs[i].start;
+	}
+
+	/* Check whether the resource range is within the hotpluggable range */
+	mhp_range = mhp_get_pluggable_range(true);
+	if (min_gpaddr < mhp_range.start)
+		min_gpaddr = mhp_range.start;
+	if (max_gpaddr > mhp_range.end)
+		max_gpaddr = mhp_range.end;
+
+	res->start = min_gpaddr;
+	res->end = max_gpaddr;
+
+	/*
+	 * Mark holes between extended regions as unavailable. The rest of that
+	 * address space will be available for the allocation.
+	 */
+	for (i = 1; i < nr_reg; i++) {
+		resource_size_t start, end;
+
+		start = regs[i - 1].end + 1;
+		end = regs[i].start - 1;
+
+		if (start > (end + 1)) {
+			rc = -EINVAL;
+			goto err;
+		}
+
+		/* There is no hole between regions */
+		if (start == (end + 1))
+			continue;
+
+		/* Check whether the hole range is within the resource range */
+		if (start < res->start || end > res->end) {
+			if (start < res->start)
+				start = res->start;
+			if (end > res->end)
+				end = res->end;
+
+			if (start >= (end + 1))
+				continue;
+		}
+
+		tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
+		if (!tmp_res) {
+			rc = -ENOMEM;
+			goto err;
+		}
+
+		tmp_res->name = "Unavailable space";
+		tmp_res->start = start;
+		tmp_res->end = end;
+
+		rc = insert_resource(res, tmp_res);
+		if (rc) {
+			pr_err("Cannot insert resource [%llx - %llx] %d\n",
+					tmp_res->start, tmp_res->end, rc);
+			kfree(tmp_res);
+			goto err;
+		}
+	}
+
+err:
+	kfree(regs);
+
+	return rc;
+}
+#endif
+
 static void __init xen_dt_guest_init(void)
 {
 	struct device_node *xen_node;
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 1b2c3ac..e6031fc 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -297,7 +297,7 @@ config XEN_FRONT_PGDIR_SHBUF
 
 config XEN_UNPOPULATED_ALLOC
 	bool "Use unpopulated memory ranges for guest mappings"
-	depends on X86 && ZONE_DEVICE
+	depends on ZONE_DEVICE
 	default XEN_BACKEND || XEN_GNTDEV || XEN_DOM0
 	help
 	  Use unpopulated memory ranges in order to create mappings for guest
-- 
2.7.4


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 2/4] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT

[Stefano Stabellini]

On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> 
> Read the start address of the grant table space from DT
> (region 0).
> 
> This patch mostly restores behaviour before commit 3cf4095d7446
> ("arm/xen: Use xen_xlate_map_ballooned_pages to setup grant table")
> but trying not to break the ACPI support added after that commit.
> So the patch touches DT part only and leaves the ACPI part with
> xen_xlate_map_ballooned_pages().
> 
> This is a preparation for using Xen extended region feature
> where unused regions of guest physical address space (provided
> by the hypervisor) will be used to create grant/foreign/whatever
> mappings instead of wasting real RAM pages from the domain memory
> for establishing these mappings.
> 
> The immediate benefit of this change:
> - Avoid superpage shattering in Xen P2M when establishing
>   stage-2 mapping (GFN <-> MFN) for the grant table space
> - Avoid wasting real RAM pages (reducing the amount of memory
>   usuable) for mapping grant table space
> - The grant table space is always mapped at the exact
>   same place (region 0 is reserved for the grant table)
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> ---
> Changes RFC -> V2:
>    - new patch
> ---
>  arch/arm/xen/enlighten.c | 32 +++++++++++++++++++++++++-------
>  1 file changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 7f1c106b..dea46ec 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -59,6 +59,9 @@ unsigned long xen_released_pages;
>  struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
>  
>  static __read_mostly unsigned int xen_events_irq;
> +static phys_addr_t xen_grant_frames;

__read_mostly


> +#define GRANT_TABLE_INDEX   0
>  
>  uint32_t xen_start_flags;
>  EXPORT_SYMBOL(xen_start_flags);
> @@ -303,6 +306,7 @@ static void __init xen_acpi_guest_init(void)
>  static void __init xen_dt_guest_init(void)
>  {
>  	struct device_node *xen_node;
> +	struct resource res;
>  
>  	xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
>  	if (!xen_node) {
> @@ -310,6 +314,12 @@ static void __init xen_dt_guest_init(void)
>  		return;
>  	}
>  
> +	if (of_address_to_resource(xen_node, GRANT_TABLE_INDEX, &res)) {
> +		pr_err("Xen grant table region is not found\n");
> +		return;
> +	}
> +	xen_grant_frames = res.start;
> +
>  	xen_events_irq = irq_of_parse_and_map(xen_node, 0);
>  }
>  
> @@ -317,16 +327,20 @@ static int __init xen_guest_init(void)
>  {
>  	struct xen_add_to_physmap xatp;
>  	struct shared_info *shared_info_page = NULL;
> -	int cpu;
> +	int rc, cpu;
>  
>  	if (!xen_domain())
>  		return 0;
>  
>  	if (!acpi_disabled)
>  		xen_acpi_guest_init();
> -	else
> +	else {
>  		xen_dt_guest_init();
>  
> +		if (!xen_grant_frames)
> +			return -ENODEV;

maybe we can avoid this, see below


> +	}
> +
>  	if (!xen_events_irq) {
>  		pr_err("Xen event channel interrupt not found\n");
>  		return -ENODEV;
> @@ -370,12 +384,16 @@ static int __init xen_guest_init(void)
>  	for_each_possible_cpu(cpu)
>  		per_cpu(xen_vcpu_id, cpu) = cpu;
>  
> -	xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
> -	if (xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
> -					  &xen_auto_xlat_grant_frames.vaddr,
> -					  xen_auto_xlat_grant_frames.count)) {
> +	if (!acpi_disabled) {

To make the code more resilient couldn't we do:

if (!acpi_disabled || !xen_grant_frames) {


> +		xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
> +		rc = xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
> +										   &xen_auto_xlat_grant_frames.vaddr,
> +										   xen_auto_xlat_grant_frames.count);
> +	} else
> +		rc = gnttab_setup_auto_xlat_frames(xen_grant_frames);
> +	if (rc) {
>  		free_percpu(xen_vcpu_info);
> -		return -ENOMEM;
> +		return rc;
>  	}
>  	gnttab_init();


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 4/4] arm/xen: Read extended regions from DT and init Xen resource

[Stefano Stabellini]

[-- Attachment #1: Type: text/plain, Size: 6204 bytes --]

On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> 
> This patch implements arch_xen_unpopulated_init() on Arm where
> the extended regions (if any) are gathered from DT and inserted
> into passed Xen resource to be used as unused address space
> for Xen scratch pages by unpopulated-alloc code.
> 
> The extended region (safe range) is a region of guest physical
> address space which is unused and could be safely used to create
> grant/foreign mappings instead of wasting real RAM pages from
> the domain memory for establishing these mappings.
> 
> The extended regions are chosen by the hypervisor at the domain
> creation time and advertised to it via "reg" property under
> hypervisor node in the guest device-tree. As region 0 is reserved
> for grant table space (always present), the indexes for extended
> regions are 1...N.
> 
> If arch_xen_unpopulated_init() fails for some reason the default
> behaviour will be restored (allocate xenballooned pages).
> 
> This patch also removes XEN_UNPOPULATED_ALLOC dependency on x86.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> ---
> Changes RFC -> V2:
>    - new patch, instead of
>     "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide unallocated space"
> ---
>  arch/arm/xen/enlighten.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/xen/Kconfig      |   2 +-
>  2 files changed, 113 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index dea46ec..1a1e0d3 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -62,6 +62,7 @@ static __read_mostly unsigned int xen_events_irq;
>  static phys_addr_t xen_grant_frames;
>  
>  #define GRANT_TABLE_INDEX   0
> +#define EXT_REGION_INDEX    1
>  
>  uint32_t xen_start_flags;
>  EXPORT_SYMBOL(xen_start_flags);
> @@ -303,6 +304,117 @@ static void __init xen_acpi_guest_init(void)
>  #endif
>  }
>  
> +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
> +int arch_xen_unpopulated_init(struct resource *res)
> +{
> +	struct device_node *np;
> +	struct resource *regs, *tmp_res;
> +	uint64_t min_gpaddr = -1, max_gpaddr = 0;
> +	unsigned int i, nr_reg = 0;
> +	struct range mhp_range;
> +	int rc;
> +
> +	if (!xen_domain())
> +		return -ENODEV;
> +
> +	np = of_find_compatible_node(NULL, NULL, "xen,xen");
> +	if (WARN_ON(!np))
> +		return -ENODEV;
> +
> +	/* Skip region 0 which is reserved for grant table space */
> +	while (of_get_address(np, nr_reg + EXT_REGION_INDEX, NULL, NULL))
> +		nr_reg++;
> +	if (!nr_reg) {
> +		pr_err("No extended regions are found\n");
> +		return -EINVAL;
> +	}
> +
> +	regs = kcalloc(nr_reg, sizeof(*regs), GFP_KERNEL);
> +	if (!regs)
> +		return -ENOMEM;
> +
> +	/*
> +	 * Create resource from extended regions provided by the hypervisor to be
> +	 * used as unused address space for Xen scratch pages.
> +	 */
> +	for (i = 0; i < nr_reg; i++) {
> +		rc = of_address_to_resource(np, i + EXT_REGION_INDEX, &regs[i]);
> +		if (rc)
> +			goto err;
> +
> +		if (max_gpaddr < regs[i].end)
> +			max_gpaddr = regs[i].end;
> +		if (min_gpaddr > regs[i].start)
> +			min_gpaddr = regs[i].start;
> +	}
> +
> +	/* Check whether the resource range is within the hotpluggable range */
> +	mhp_range = mhp_get_pluggable_range(true);
> +	if (min_gpaddr < mhp_range.start)
> +		min_gpaddr = mhp_range.start;
> +	if (max_gpaddr > mhp_range.end)
> +		max_gpaddr = mhp_range.end;
> +
> +	res->start = min_gpaddr;
> +	res->end = max_gpaddr;
> +
> +	/*
> +	 * Mark holes between extended regions as unavailable. The rest of that
> +	 * address space will be available for the allocation.
> +	 */
> +	for (i = 1; i < nr_reg; i++) {
> +		resource_size_t start, end;
> +
> +		start = regs[i - 1].end + 1;
> +		end = regs[i].start - 1;
> +
> +		if (start > (end + 1)) {

Should this be:

if (start >= end)

?


> +			rc = -EINVAL;
> +			goto err;
> +		}
> +
> +		/* There is no hole between regions */
> +		if (start == (end + 1))

Also here, shouldn't it be:

if (start == end)

?

I think I am missing again something in termination accounting :-)


> +			continue;
> +
> +		/* Check whether the hole range is within the resource range */
> +		if (start < res->start || end > res->end) {

By definition I don't think this check is necessary as either condition
is impossible?


> +			if (start < res->start)
> +				start = res->start;
> +			if (end > res->end)
> +				end = res->end;
> +
> +			if (start >= (end + 1))
> +				continue;
> +		}
> +
> +		tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
> +		if (!tmp_res) {
> +			rc = -ENOMEM;
> +			goto err;
> +		}
> +
> +		tmp_res->name = "Unavailable space";
> +		tmp_res->start = start;
> +		tmp_res->end = end;

Do we need to set any flags so that the system can reuse the memory in
the hole, e.g. IORESOURCE_MEM? Or is it not necessary?


> +		rc = insert_resource(res, tmp_res);
> +		if (rc) {
> +			pr_err("Cannot insert resource [%llx - %llx] %d\n",
> +					tmp_res->start, tmp_res->end, rc);

Although it is impossible to enable XEN_UNPOPULATED_ALLOC on arm32 due
to unmet dependencies, I would like to keep the implementation of
arch_xen_unpopulated_init 32bit clean.

I am getting build errors like (by forcing arch_xen_unpopulated_init to
compile on arm32):

./include/linux/kern_levels.h:5:18: warning: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘resource_size_t {aka unsigned int}’ [-Wformat=]


> +			kfree(tmp_res);
> +			goto err;
> +		}
> +	}
> +
> +err:
> +	kfree(regs);
> +
> +	return rc;
> +}
> +#endif
> +
>  static void __init xen_dt_guest_init(void)
>  {
>  	struct device_node *xen_node;
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 1b2c3ac..e6031fc 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -297,7 +297,7 @@ config XEN_FRONT_PGDIR_SHBUF
>  
>  config XEN_UNPOPULATED_ALLOC
>  	bool "Use unpopulated memory ranges for guest mappings"
> -	depends on X86 && ZONE_DEVICE
> +	depends on ZONE_DEVICE
>  	default XEN_BACKEND || XEN_GNTDEV || XEN_DOM0
>  	help
>  	  Use unpopulated memory ranges in order to create mappings for guest

[-- Attachment #2: Type: text/plain, Size: 176 bytes --]

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 4/4] arm/xen: Read extended regions from DT and init Xen resource

[Oleksandr]

On 28.10.21 04:40, Stefano Stabellini wrote:

Hi Stefano

I am sorry for the late response.

> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> This patch implements arch_xen_unpopulated_init() on Arm where
>> the extended regions (if any) are gathered from DT and inserted
>> into passed Xen resource to be used as unused address space
>> for Xen scratch pages by unpopulated-alloc code.
>>
>> The extended region (safe range) is a region of guest physical
>> address space which is unused and could be safely used to create
>> grant/foreign mappings instead of wasting real RAM pages from
>> the domain memory for establishing these mappings.
>>
>> The extended regions are chosen by the hypervisor at the domain
>> creation time and advertised to it via "reg" property under
>> hypervisor node in the guest device-tree. As region 0 is reserved
>> for grant table space (always present), the indexes for extended
>> regions are 1...N.
>>
>> If arch_xen_unpopulated_init() fails for some reason the default
>> behaviour will be restored (allocate xenballooned pages).
>>
>> This patch also removes XEN_UNPOPULATED_ALLOC dependency on x86.
>>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>> ---
>> Changes RFC -> V2:
>>     - new patch, instead of
>>      "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide unallocated space"
>> ---
>>   arch/arm/xen/enlighten.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++
>>   drivers/xen/Kconfig      |   2 +-
>>   2 files changed, 113 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
>> index dea46ec..1a1e0d3 100644
>> --- a/arch/arm/xen/enlighten.c
>> +++ b/arch/arm/xen/enlighten.c
>> @@ -62,6 +62,7 @@ static __read_mostly unsigned int xen_events_irq;
>>   static phys_addr_t xen_grant_frames;
>>   
>>   #define GRANT_TABLE_INDEX   0
>> +#define EXT_REGION_INDEX    1
>>   
>>   uint32_t xen_start_flags;
>>   EXPORT_SYMBOL(xen_start_flags);
>> @@ -303,6 +304,117 @@ static void __init xen_acpi_guest_init(void)
>>   #endif
>>   }
>>   
>> +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
>> +int arch_xen_unpopulated_init(struct resource *res)
>> +{
>> +	struct device_node *np;
>> +	struct resource *regs, *tmp_res;
>> +	uint64_t min_gpaddr = -1, max_gpaddr = 0;
>> +	unsigned int i, nr_reg = 0;
>> +	struct range mhp_range;
>> +	int rc;
>> +
>> +	if (!xen_domain())
>> +		return -ENODEV;
>> +
>> +	np = of_find_compatible_node(NULL, NULL, "xen,xen");
>> +	if (WARN_ON(!np))
>> +		return -ENODEV;
>> +
>> +	/* Skip region 0 which is reserved for grant table space */
>> +	while (of_get_address(np, nr_reg + EXT_REGION_INDEX, NULL, NULL))
>> +		nr_reg++;
>> +	if (!nr_reg) {
>> +		pr_err("No extended regions are found\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	regs = kcalloc(nr_reg, sizeof(*regs), GFP_KERNEL);
>> +	if (!regs)
>> +		return -ENOMEM;
>> +
>> +	/*
>> +	 * Create resource from extended regions provided by the hypervisor to be
>> +	 * used as unused address space for Xen scratch pages.
>> +	 */
>> +	for (i = 0; i < nr_reg; i++) {
>> +		rc = of_address_to_resource(np, i + EXT_REGION_INDEX, &regs[i]);
>> +		if (rc)
>> +			goto err;
>> +
>> +		if (max_gpaddr < regs[i].end)
>> +			max_gpaddr = regs[i].end;
>> +		if (min_gpaddr > regs[i].start)
>> +			min_gpaddr = regs[i].start;
>> +	}
>> +
>> +	/* Check whether the resource range is within the hotpluggable range */
>> +	mhp_range = mhp_get_pluggable_range(true);
>> +	if (min_gpaddr < mhp_range.start)
>> +		min_gpaddr = mhp_range.start;
>> +	if (max_gpaddr > mhp_range.end)
>> +		max_gpaddr = mhp_range.end;
>> +
>> +	res->start = min_gpaddr;
>> +	res->end = max_gpaddr;
>> +
>> +	/*
>> +	 * Mark holes between extended regions as unavailable. The rest of that
>> +	 * address space will be available for the allocation.
>> +	 */
>> +	for (i = 1; i < nr_reg; i++) {
>> +		resource_size_t start, end;
>> +
>> +		start = regs[i - 1].end + 1;
>> +		end = regs[i].start - 1;
>> +
>> +		if (start > (end + 1)) {
> Should this be:
>
> if (start >= end)
>
> ?

Yes, we can do this here (since the checks are equivalent) but ...


>
>
>> +			rc = -EINVAL;
>> +			goto err;
>> +		}
>> +
>> +		/* There is no hole between regions */
>> +		if (start == (end + 1))
> Also here, shouldn't it be:
>
> if (start == end)
>
> ?

    ... not here.

As

"(start == (end + 1))" is equal to "(regs[i - 1].end + 1 == regs[i].start)"

but

"(start == end)" is equal to "(regs[i - 1].end + 1 == regs[i].start - 1)"


>
> I think I am missing again something in termination accounting :-)

If I understand correctly, we need to follow "end = start + size - 1" 
rule, so the "end" is the last address inside a range, but not the 
"first" address outside of a range))


>
>
>> +			continue;
>> +
>> +		/* Check whether the hole range is within the resource range */
>> +		if (start < res->start || end > res->end) {
> By definition I don't think this check is necessary as either condition
> is impossible?


This is a good question, let me please explain.
Not all extended regions provided by the hypervisor can be used here. 
This is because the addressable physical memory range for which the 
linear mapping
could be created has limits on Arm, and maximum addressable range 
depends on the VA space size (CONFIG_ARM64_VA_BITS_XXX). So we decided 
to not filter them in hypervisor as this logic could be quite complex as 
different OS may have different requirement, etc. This means that we 
need to make sure that regions are within the hotpluggable range to 
avoid a failure later on when a region is pre-validated by the memory 
hotplug path.

The following code limits the resource range based on that:

+    /* Check whether the resource range is within the hotpluggable range */
+    mhp_range = mhp_get_pluggable_range(true);
+    if (min_gpaddr < mhp_range.start)
+        min_gpaddr = mhp_range.start;
+    if (max_gpaddr > mhp_range.end)
+        max_gpaddr = mhp_range.end;
+
+    res->start = min_gpaddr;
+    res->end = max_gpaddr;

In current loop (when calculating and inserting holes) we also need to 
make sure that resulting hole range is within the resource range (and 
adjust/skip it if not true) as regs[] used for the calculations contains 
raw regions as they described in DT so not updated. Otherwise 
insert_resource() down the function will return an error for the 
conflicting operations. Yes, I could took a different route and update 
regs[] in advance to adjust/skip non-suitable regions in front, but I 
decided to do it on the fly in the loop here, I thought doing it in 
advance would add some overhead/complexity. What do you think?

So I am afraid this check is necessary here.

For example in my environment the extended regions are:

(XEN) Extended region 0: 0->0x8000000
(XEN) Extended region 1: 0xc000000->0x30000000
(XEN) Extended region 2: 0x40000000->0x47e00000
(XEN) Extended region 3: 0xd0000000->0xe6000000
(XEN) Extended region 4: 0xe7800000->0xec000000
(XEN) Extended region 5: 0xf1200000->0xfd000000
(XEN) Extended region 6: 0x100000000->0x500000000
(XEN) Extended region 7: 0x580000000->0x600000000
(XEN) Extended region 8: 0x680000000->0x700000000
(XEN) Extended region 9: 0x780000000->0x10000000000

*With* the check the holes are:

holes [47e00000 - cfffffff]
holes [e6000000 - e77fffff]
holes [ec000000 - f11fffff]
holes [fd000000 - ffffffff]
holes [500000000 - 57fffffff]
holes [600000000 - 67fffffff]
holes [700000000 - 77fffffff]

And they seem to look correct, you can see that two possible holes 
between extended regions 0-1 (8000000-bffffff) and 1-2 
(30000000-3fffffff) were skipped as they entirely located below res->start
which is 0x40000000 in my case (48-bit VA: 0x40000000 - 0x80003fffffff).

*Without* the check these two holes won't be skipped and as the result 
insert_resource() will fail.


**********


I have one idea how we can simplify filter logic, we can drop all checks 
here (including confusing one) in Arm code and update common code a bit:

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 1a1e0d3..ed5b855 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -311,7 +311,6 @@ int arch_xen_unpopulated_init(struct resource *res)
         struct resource *regs, *tmp_res;
         uint64_t min_gpaddr = -1, max_gpaddr = 0;
         unsigned int i, nr_reg = 0;
-       struct range mhp_range;
         int rc;

         if (!xen_domain())
@@ -349,13 +348,6 @@ int arch_xen_unpopulated_init(struct resource *res)
                         min_gpaddr = regs[i].start;
         }

-       /* Check whether the resource range is within the hotpluggable 
range */
-       mhp_range = mhp_get_pluggable_range(true);
-       if (min_gpaddr < mhp_range.start)
-               min_gpaddr = mhp_range.start;
-       if (max_gpaddr > mhp_range.end)
-               max_gpaddr = mhp_range.end;
-
         res->start = min_gpaddr;
         res->end = max_gpaddr;

@@ -378,17 +370,6 @@ int arch_xen_unpopulated_init(struct resource *res)
                 if (start == (end + 1))
                         continue;

-               /* Check whether the hole range is within the resource 
range */
-               if (start < res->start || end > res->end) {
-                       if (start < res->start)
-                               start = res->start;
-                       if (end > res->end)
-                               end = res->end;
-
-                       if (start >= (end + 1))
-                               continue;
-               }
-
                 tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
                 if (!tmp_res) {
                         rc = -ENOMEM;
diff --git a/drivers/xen/unpopulated-alloc.c 
b/drivers/xen/unpopulated-alloc.c
index 1f1d8d8..a5d3ebb 100644
--- a/drivers/xen/unpopulated-alloc.c
+++ b/drivers/xen/unpopulated-alloc.c
@@ -39,6 +39,7 @@ static int fill_list(unsigned int nr_pages)
         void *vaddr;
         unsigned int i, alloc_pages = round_up(nr_pages, 
PAGES_PER_SECTION);
         int ret;
+       struct range mhp_range;

         res = kzalloc(sizeof(*res), GFP_KERNEL);
         if (!res)
@@ -47,8 +48,10 @@ static int fill_list(unsigned int nr_pages)
         res->name = "Xen scratch";
         res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;

+       mhp_range = mhp_get_pluggable_range(true);
+
         ret = allocate_resource(target_resource, res,
-                               alloc_pages * PAGE_SIZE, 0, -1,
+                               alloc_pages * PAGE_SIZE, 
mhp_range.start, mhp_range.end,
                                 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
         if (ret < 0) {
                 pr_err("Cannot allocate new IOMEM resource\n");
(END)

I believe, this will work on x86 as arch_get_mappable_range() is not 
implemented there,
and the default option contains exactly what being used currently (0, -1).

struct range __weak arch_get_mappable_range(void)
{
     struct range mhp_range = {
         .start = 0UL,
         .end = -1ULL,
     };
     return mhp_range;
}

And this is going to be more generic and clear, what do you think?


>
>> +			if (start < res->start)
>> +				start = res->start;
>> +			if (end > res->end)
>> +				end = res->end;
>> +
>> +			if (start >= (end + 1))
>> +				continue;
>> +		}
>> +
>> +		tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
>> +		if (!tmp_res) {
>> +			rc = -ENOMEM;
>> +			goto err;
>> +		}
>> +
>> +		tmp_res->name = "Unavailable space";
>> +		tmp_res->start = start;
>> +		tmp_res->end = end;
> Do we need to set any flags so that the system can reuse the memory in
> the hole, e.g. IORESOURCE_MEM? Or is it not necessary?


I might be wrong, but I don't think it is necessary. I don't see how the 
system can reuse memory in the holes as
the Xen resource we are constructing here will be exclusively used by 
the unpopulated-alloc code only. I would leave type-less
resource here. Or I missed something?


>
>
>> +		rc = insert_resource(res, tmp_res);
>> +		if (rc) {
>> +			pr_err("Cannot insert resource [%llx - %llx] %d\n",
>> +					tmp_res->start, tmp_res->end, rc);
> Although it is impossible to enable XEN_UNPOPULATED_ALLOC on arm32 due
> to unmet dependencies, I would like to keep the implementation of
> arch_xen_unpopulated_init 32bit clean.
>
> I am getting build errors like (by forcing arch_xen_unpopulated_init to
> compile on arm32):
>
> ./include/linux/kern_levels.h:5:18: warning: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘resource_size_t {aka unsigned int}’ [-Wformat=]

Thank you for pointing this out. I will use %pR specifier here and in 
the common code where I print the same message.


>
>
>> +			kfree(tmp_res);
>> +			goto err;
>> +		}
>> +	}
>> +
>> +err:
>> +	kfree(regs);
>> +
>> +	return rc;
>> +}
>> +#endif
>> +
>>   static void __init xen_dt_guest_init(void)
>>   {
>>   	struct device_node *xen_node;
>> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
>> index 1b2c3ac..e6031fc 100644
>> --- a/drivers/xen/Kconfig
>> +++ b/drivers/xen/Kconfig
>> @@ -297,7 +297,7 @@ config XEN_FRONT_PGDIR_SHBUF
>>   
>>   config XEN_UNPOPULATED_ALLOC
>>   	bool "Use unpopulated memory ranges for guest mappings"
>> -	depends on X86 && ZONE_DEVICE
>> +	depends on ZONE_DEVICE
>>   	default XEN_BACKEND || XEN_GNTDEV || XEN_DOM0
>>   	help
>>   	  Use unpopulated memory ranges in order to create mappings for guest

-- 
Regards,

Oleksandr Tyshchenko


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 2/4] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT

[Oleksandr]

On 28.10.21 04:28, Stefano Stabellini wrote:

Hi Stefano

I am sorry for the late response.

> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> Read the start address of the grant table space from DT
>> (region 0).
>>
>> This patch mostly restores behaviour before commit 3cf4095d7446
>> ("arm/xen: Use xen_xlate_map_ballooned_pages to setup grant table")
>> but trying not to break the ACPI support added after that commit.
>> So the patch touches DT part only and leaves the ACPI part with
>> xen_xlate_map_ballooned_pages().
>>
>> This is a preparation for using Xen extended region feature
>> where unused regions of guest physical address space (provided
>> by the hypervisor) will be used to create grant/foreign/whatever
>> mappings instead of wasting real RAM pages from the domain memory
>> for establishing these mappings.
>>
>> The immediate benefit of this change:
>> - Avoid superpage shattering in Xen P2M when establishing
>>    stage-2 mapping (GFN <-> MFN) for the grant table space
>> - Avoid wasting real RAM pages (reducing the amount of memory
>>    usuable) for mapping grant table space
>> - The grant table space is always mapped at the exact
>>    same place (region 0 is reserved for the grant table)
>>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>> ---
>> Changes RFC -> V2:
>>     - new patch
>> ---
>>   arch/arm/xen/enlighten.c | 32 +++++++++++++++++++++++++-------
>>   1 file changed, 25 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
>> index 7f1c106b..dea46ec 100644
>> --- a/arch/arm/xen/enlighten.c
>> +++ b/arch/arm/xen/enlighten.c
>> @@ -59,6 +59,9 @@ unsigned long xen_released_pages;
>>   struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
>>   
>>   static __read_mostly unsigned int xen_events_irq;
>> +static phys_addr_t xen_grant_frames;
> __read_mostly

ok


>
>
>> +#define GRANT_TABLE_INDEX   0
>>   
>>   uint32_t xen_start_flags;
>>   EXPORT_SYMBOL(xen_start_flags);
>> @@ -303,6 +306,7 @@ static void __init xen_acpi_guest_init(void)
>>   static void __init xen_dt_guest_init(void)
>>   {
>>   	struct device_node *xen_node;
>> +	struct resource res;
>>   
>>   	xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
>>   	if (!xen_node) {
>> @@ -310,6 +314,12 @@ static void __init xen_dt_guest_init(void)
>>   		return;
>>   	}
>>   
>> +	if (of_address_to_resource(xen_node, GRANT_TABLE_INDEX, &res)) {
>> +		pr_err("Xen grant table region is not found\n");
>> +		return;
>> +	}
>> +	xen_grant_frames = res.start;
>> +
>>   	xen_events_irq = irq_of_parse_and_map(xen_node, 0);
>>   }
>>   
>> @@ -317,16 +327,20 @@ static int __init xen_guest_init(void)
>>   {
>>   	struct xen_add_to_physmap xatp;
>>   	struct shared_info *shared_info_page = NULL;
>> -	int cpu;
>> +	int rc, cpu;
>>   
>>   	if (!xen_domain())
>>   		return 0;
>>   
>>   	if (!acpi_disabled)
>>   		xen_acpi_guest_init();
>> -	else
>> +	else {
>>   		xen_dt_guest_init();
>>   
>> +		if (!xen_grant_frames)
>> +			return -ENODEV;
> maybe we can avoid this, see below
>
>
>> +	}
>> +
>>   	if (!xen_events_irq) {
>>   		pr_err("Xen event channel interrupt not found\n");
>>   		return -ENODEV;
>> @@ -370,12 +384,16 @@ static int __init xen_guest_init(void)
>>   	for_each_possible_cpu(cpu)
>>   		per_cpu(xen_vcpu_id, cpu) = cpu;
>>   
>> -	xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
>> -	if (xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
>> -					  &xen_auto_xlat_grant_frames.vaddr,
>> -					  xen_auto_xlat_grant_frames.count)) {
>> +	if (!acpi_disabled) {
> To make the code more resilient couldn't we do:
>
> if (!acpi_disabled || !xen_grant_frames) {
I think, we can.

On the one hand, indeed the code more resilient and less change.
 From the other hand if grant table region is not found then something 
weird happened as region 0 is always present in reg property if 
hypervisor node is exposed to the guest.
The behavior before commit 3cf4095d7446 ("arm/xen: Use 
xen_xlate_map_ballooned_pages to setup grant table") was exactly the 
same in the context of the failure if region wasn't found.

...

Well, if we want to make code more resilient, I will update. But, looks 
like we also need to switch actions in xen_dt_guest_init() in order to 
process xen_events_irq before xen_grant_frames, otherwise we may return 
after failing with region and end up not initializing xen_events_irq so 
xen_guest_init() will fail earlier than reaches that check.
What do you think?


>
>> +		xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
>> +		rc = xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
>> +										   &xen_auto_xlat_grant_frames.vaddr,
>> +										   xen_auto_xlat_grant_frames.count);
>> +	} else
>> +		rc = gnttab_setup_auto_xlat_frames(xen_grant_frames);
>> +	if (rc) {
>>   		free_percpu(xen_vcpu_info);
>> -		return -ENOMEM;
>> +		return rc;
>>   	}
>>   	gnttab_init();

-- 
Regards,

Oleksandr Tyshchenko


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 2/4] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT

[Stefano Stabellini]

On Thu, 11 Nov 2021, Oleksandr wrote:
> On 28.10.21 04:28, Stefano Stabellini wrote:
> 
> Hi Stefano
> 
> I am sorry for the late response.
> 
> > On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
> > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > 
> > > Read the start address of the grant table space from DT
> > > (region 0).
> > > 
> > > This patch mostly restores behaviour before commit 3cf4095d7446
> > > ("arm/xen: Use xen_xlate_map_ballooned_pages to setup grant table")
> > > but trying not to break the ACPI support added after that commit.
> > > So the patch touches DT part only and leaves the ACPI part with
> > > xen_xlate_map_ballooned_pages().
> > > 
> > > This is a preparation for using Xen extended region feature
> > > where unused regions of guest physical address space (provided
> > > by the hypervisor) will be used to create grant/foreign/whatever
> > > mappings instead of wasting real RAM pages from the domain memory
> > > for establishing these mappings.
> > > 
> > > The immediate benefit of this change:
> > > - Avoid superpage shattering in Xen P2M when establishing
> > >    stage-2 mapping (GFN <-> MFN) for the grant table space
> > > - Avoid wasting real RAM pages (reducing the amount of memory
> > >    usuable) for mapping grant table space
> > > - The grant table space is always mapped at the exact
> > >    same place (region 0 is reserved for the grant table)
> > > 
> > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > ---
> > > Changes RFC -> V2:
> > >     - new patch
> > > ---
> > >   arch/arm/xen/enlighten.c | 32 +++++++++++++++++++++++++-------
> > >   1 file changed, 25 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > > index 7f1c106b..dea46ec 100644
> > > --- a/arch/arm/xen/enlighten.c
> > > +++ b/arch/arm/xen/enlighten.c
> > > @@ -59,6 +59,9 @@ unsigned long xen_released_pages;
> > >   struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS]
> > > __initdata;
> > >     static __read_mostly unsigned int xen_events_irq;
> > > +static phys_addr_t xen_grant_frames;
> > __read_mostly
> 
> ok
> 
> 
> > 
> > 
> > > +#define GRANT_TABLE_INDEX   0
> > >     uint32_t xen_start_flags;
> > >   EXPORT_SYMBOL(xen_start_flags);
> > > @@ -303,6 +306,7 @@ static void __init xen_acpi_guest_init(void)
> > >   static void __init xen_dt_guest_init(void)
> > >   {
> > >   	struct device_node *xen_node;
> > > +	struct resource res;
> > >     	xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
> > >   	if (!xen_node) {
> > > @@ -310,6 +314,12 @@ static void __init xen_dt_guest_init(void)
> > >   		return;
> > >   	}
> > >   +	if (of_address_to_resource(xen_node, GRANT_TABLE_INDEX, &res)) {
> > > +		pr_err("Xen grant table region is not found\n");
> > > +		return;
> > > +	}
> > > +	xen_grant_frames = res.start;
> > > +
> > >   	xen_events_irq = irq_of_parse_and_map(xen_node, 0);
> > >   }
> > >   @@ -317,16 +327,20 @@ static int __init xen_guest_init(void)
> > >   {
> > >   	struct xen_add_to_physmap xatp;
> > >   	struct shared_info *shared_info_page = NULL;
> > > -	int cpu;
> > > +	int rc, cpu;
> > >     	if (!xen_domain())
> > >   		return 0;
> > >     	if (!acpi_disabled)
> > >   		xen_acpi_guest_init();
> > > -	else
> > > +	else {
> > >   		xen_dt_guest_init();
> > >   +		if (!xen_grant_frames)
> > > +			return -ENODEV;
> > maybe we can avoid this, see below
> > 
> > 
> > > +	}
> > > +
> > >   	if (!xen_events_irq) {
> > >   		pr_err("Xen event channel interrupt not found\n");
> > >   		return -ENODEV;
> > > @@ -370,12 +384,16 @@ static int __init xen_guest_init(void)
> > >   	for_each_possible_cpu(cpu)
> > >   		per_cpu(xen_vcpu_id, cpu) = cpu;
> > >   -	xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
> > > -	if (xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
> > > -					  &xen_auto_xlat_grant_frames.vaddr,
> > > -					  xen_auto_xlat_grant_frames.count)) {
> > > +	if (!acpi_disabled) {
> > To make the code more resilient couldn't we do:
> > 
> > if (!acpi_disabled || !xen_grant_frames) {
> I think, we can.
> 
> On the one hand, indeed the code more resilient and less change.
> From the other hand if grant table region is not found then something weird
> happened as region 0 is always present in reg property if hypervisor node is
> exposed to the guest.
> The behavior before commit 3cf4095d7446 ("arm/xen: Use
> xen_xlate_map_ballooned_pages to setup grant table") was exactly the same in
> the context of the failure if region wasn't found.
> 
> ...
> 
> Well, if we want to make code more resilient, I will update. But, looks like
> we also need to switch actions in xen_dt_guest_init() in order to process
> xen_events_irq before xen_grant_frames, otherwise we may return after failing
> with region and end up not initializing xen_events_irq so xen_guest_init()
> will fail earlier than reaches that check.
> What do you think?
 
Yes, you are right. I was re-reading the patch to refresh my memory and
I noticed immediately that xen_dt_guest_init also need to be changed so
that xen_events_irq is set before xen_grant_frames.
 
I think it is a minor change that doesn't add complexity but make the
code more robust so I think it is a good idea

 
> > > +		xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
> > > +		rc =
> > > xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
> > > +
> > > &xen_auto_xlat_grant_frames.vaddr,
> > > +
> > > xen_auto_xlat_grant_frames.count);
> > > +	} else
> > > +		rc = gnttab_setup_auto_xlat_frames(xen_grant_frames);
> > > +	if (rc) {
> > >   		free_percpu(xen_vcpu_info);
> > > -		return -ENOMEM;
> > > +		return rc;
> > >   	}
> > >   	gnttab_init();


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 4/4] arm/xen: Read extended regions from DT and init Xen resource

[Stefano Stabellini]

[-- Attachment #1: Type: text/plain, Size: 12819 bytes --]

On Wed, 10 Nov 2021, Oleksandr wrote:
> On 28.10.21 04:40, Stefano Stabellini wrote:
> 
> Hi Stefano
> 
> I am sorry for the late response.
> 
> > On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
> > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > 
> > > This patch implements arch_xen_unpopulated_init() on Arm where
> > > the extended regions (if any) are gathered from DT and inserted
> > > into passed Xen resource to be used as unused address space
> > > for Xen scratch pages by unpopulated-alloc code.
> > > 
> > > The extended region (safe range) is a region of guest physical
> > > address space which is unused and could be safely used to create
> > > grant/foreign mappings instead of wasting real RAM pages from
> > > the domain memory for establishing these mappings.
> > > 
> > > The extended regions are chosen by the hypervisor at the domain
> > > creation time and advertised to it via "reg" property under
> > > hypervisor node in the guest device-tree. As region 0 is reserved
> > > for grant table space (always present), the indexes for extended
> > > regions are 1...N.
> > > 
> > > If arch_xen_unpopulated_init() fails for some reason the default
> > > behaviour will be restored (allocate xenballooned pages).
> > > 
> > > This patch also removes XEN_UNPOPULATED_ALLOC dependency on x86.
> > > 
> > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > ---
> > > Changes RFC -> V2:
> > >     - new patch, instead of
> > >      "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide
> > > unallocated space"
> > > ---
> > >   arch/arm/xen/enlighten.c | 112
> > > +++++++++++++++++++++++++++++++++++++++++++++++
> > >   drivers/xen/Kconfig      |   2 +-
> > >   2 files changed, 113 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > > index dea46ec..1a1e0d3 100644
> > > --- a/arch/arm/xen/enlighten.c
> > > +++ b/arch/arm/xen/enlighten.c
> > > @@ -62,6 +62,7 @@ static __read_mostly unsigned int xen_events_irq;
> > >   static phys_addr_t xen_grant_frames;
> > >     #define GRANT_TABLE_INDEX   0
> > > +#define EXT_REGION_INDEX    1
> > >     uint32_t xen_start_flags;
> > >   EXPORT_SYMBOL(xen_start_flags);
> > > @@ -303,6 +304,117 @@ static void __init xen_acpi_guest_init(void)
> > >   #endif
> > >   }
> > >   +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
> > > +int arch_xen_unpopulated_init(struct resource *res)
> > > +{
> > > +	struct device_node *np;
> > > +	struct resource *regs, *tmp_res;
> > > +	uint64_t min_gpaddr = -1, max_gpaddr = 0;
> > > +	unsigned int i, nr_reg = 0;
> > > +	struct range mhp_range;
> > > +	int rc;
> > > +
> > > +	if (!xen_domain())
> > > +		return -ENODEV;
> > > +
> > > +	np = of_find_compatible_node(NULL, NULL, "xen,xen");
> > > +	if (WARN_ON(!np))
> > > +		return -ENODEV;
> > > +
> > > +	/* Skip region 0 which is reserved for grant table space */
> > > +	while (of_get_address(np, nr_reg + EXT_REGION_INDEX, NULL, NULL))
> > > +		nr_reg++;
> > > +	if (!nr_reg) {
> > > +		pr_err("No extended regions are found\n");
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	regs = kcalloc(nr_reg, sizeof(*regs), GFP_KERNEL);
> > > +	if (!regs)
> > > +		return -ENOMEM;
> > > +
> > > +	/*
> > > +	 * Create resource from extended regions provided by the hypervisor to
> > > be
> > > +	 * used as unused address space for Xen scratch pages.
> > > +	 */
> > > +	for (i = 0; i < nr_reg; i++) {
> > > +		rc = of_address_to_resource(np, i + EXT_REGION_INDEX,
> > > &regs[i]);
> > > +		if (rc)
> > > +			goto err;
> > > +
> > > +		if (max_gpaddr < regs[i].end)
> > > +			max_gpaddr = regs[i].end;
> > > +		if (min_gpaddr > regs[i].start)
> > > +			min_gpaddr = regs[i].start;
> > > +	}
> > > +
> > > +	/* Check whether the resource range is within the hotpluggable range
> > > */
> > > +	mhp_range = mhp_get_pluggable_range(true);
> > > +	if (min_gpaddr < mhp_range.start)
> > > +		min_gpaddr = mhp_range.start;
> > > +	if (max_gpaddr > mhp_range.end)
> > > +		max_gpaddr = mhp_range.end;
> > > +
> > > +	res->start = min_gpaddr;
> > > +	res->end = max_gpaddr;
> > > +
> > > +	/*
> > > +	 * Mark holes between extended regions as unavailable. The rest of
> > > that
> > > +	 * address space will be available for the allocation.
> > > +	 */
> > > +	for (i = 1; i < nr_reg; i++) {
> > > +		resource_size_t start, end;
> > > +
> > > +		start = regs[i - 1].end + 1;
> > > +		end = regs[i].start - 1;
> > > +
> > > +		if (start > (end + 1)) {
> > Should this be:
> > 
> > if (start >= end)
> > 
> > ?
> 
> Yes, we can do this here (since the checks are equivalent) but ...
>
> > > +			rc = -EINVAL;
> > > +			goto err;
> > > +		}
> > > +
> > > +		/* There is no hole between regions */
> > > +		if (start == (end + 1))
> > Also here, shouldn't it be:
> > 
> > if (start == end)
> > 
> > ?
> 
>    ... not here.
> 
> As
> 
> "(start == (end + 1))" is equal to "(regs[i - 1].end + 1 == regs[i].start)"
> 
> but
> 
> "(start == end)" is equal to "(regs[i - 1].end + 1 == regs[i].start - 1)"
 
OK. But the check:

  if (start >= end)

Actually covers both cases so that's the only check we need?


> > 
> > I think I am missing again something in termination accounting :-)
> 
> If I understand correctly, we need to follow "end = start + size - 1" rule, so
> the "end" is the last address inside a range, but not the "first" address
> outside of a range))

yeah
 

> > > +			continue;
> > > +
> > > +		/* Check whether the hole range is within the resource range
> > > */
> > > +		if (start < res->start || end > res->end) {
> > By definition I don't think this check is necessary as either condition
> > is impossible?
> 
> 
> This is a good question, let me please explain.
> Not all extended regions provided by the hypervisor can be used here. This is
> because the addressable physical memory range for which the linear mapping
> could be created has limits on Arm, and maximum addressable range depends on
> the VA space size (CONFIG_ARM64_VA_BITS_XXX). So we decided to not filter them
> in hypervisor as this logic could be quite complex as different OS may have
> different requirement, etc. This means that we need to make sure that regions
> are within the hotpluggable range to avoid a failure later on when a region is
> pre-validated by the memory hotplug path.
> 
> The following code limits the resource range based on that:
> 
> +    /* Check whether the resource range is within the hotpluggable range */
> +    mhp_range = mhp_get_pluggable_range(true);
> +    if (min_gpaddr < mhp_range.start)
> +        min_gpaddr = mhp_range.start;
> +    if (max_gpaddr > mhp_range.end)
> +        max_gpaddr = mhp_range.end;
> +
> +    res->start = min_gpaddr;
> +    res->end = max_gpaddr;
> 
> In current loop (when calculating and inserting holes) we also need to make
> sure that resulting hole range is within the resource range (and adjust/skip
> it if not true) as regs[] used for the calculations contains raw regions as
> they described in DT so not updated. Otherwise insert_resource() down the
> function will return an error for the conflicting operations. Yes, I could
> took a different route and update regs[] in advance to adjust/skip
> non-suitable regions in front, but I decided to do it on the fly in the loop
> here, I thought doing it in advance would add some overhead/complexity. What
> do you think?

I understand now.


> So I am afraid this check is necessary here.
> 
> For example in my environment the extended regions are:
> 
> (XEN) Extended region 0: 0->0x8000000
> (XEN) Extended region 1: 0xc000000->0x30000000
> (XEN) Extended region 2: 0x40000000->0x47e00000
> (XEN) Extended region 3: 0xd0000000->0xe6000000
> (XEN) Extended region 4: 0xe7800000->0xec000000
> (XEN) Extended region 5: 0xf1200000->0xfd000000
> (XEN) Extended region 6: 0x100000000->0x500000000
> (XEN) Extended region 7: 0x580000000->0x600000000
> (XEN) Extended region 8: 0x680000000->0x700000000
> (XEN) Extended region 9: 0x780000000->0x10000000000
> 
> *With* the check the holes are:
> 
> holes [47e00000 - cfffffff]
> holes [e6000000 - e77fffff]
> holes [ec000000 - f11fffff]
> holes [fd000000 - ffffffff]
> holes [500000000 - 57fffffff]
> holes [600000000 - 67fffffff]
> holes [700000000 - 77fffffff]
> 
> And they seem to look correct, you can see that two possible holes between
> extended regions 0-1 (8000000-bffffff) and 1-2 (30000000-3fffffff) were
> skipped as they entirely located below res->start
> which is 0x40000000 in my case (48-bit VA: 0x40000000 - 0x80003fffffff).
> 
> *Without* the check these two holes won't be skipped and as the result
> insert_resource() will fail.
> 
> 
> **********
> 
> 
> I have one idea how we can simplify filter logic, we can drop all checks here
> (including confusing one) in Arm code and update common code a bit:
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 1a1e0d3..ed5b855 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -311,7 +311,6 @@ int arch_xen_unpopulated_init(struct resource *res)
>         struct resource *regs, *tmp_res;
>         uint64_t min_gpaddr = -1, max_gpaddr = 0;
>         unsigned int i, nr_reg = 0;
> -       struct range mhp_range;
>         int rc;
> 
>         if (!xen_domain())
> @@ -349,13 +348,6 @@ int arch_xen_unpopulated_init(struct resource *res)
>                         min_gpaddr = regs[i].start;
>         }
> 
> -       /* Check whether the resource range is within the hotpluggable range
> */
> -       mhp_range = mhp_get_pluggable_range(true);
> -       if (min_gpaddr < mhp_range.start)
> -               min_gpaddr = mhp_range.start;
> -       if (max_gpaddr > mhp_range.end)
> -               max_gpaddr = mhp_range.end;
> -
>         res->start = min_gpaddr;
>         res->end = max_gpaddr;
> 
> @@ -378,17 +370,6 @@ int arch_xen_unpopulated_init(struct resource *res)
>                 if (start == (end + 1))
>                         continue;
> 
> -               /* Check whether the hole range is within the resource range
> */
> -               if (start < res->start || end > res->end) {
> -                       if (start < res->start)
> -                               start = res->start;
> -                       if (end > res->end)
> -                               end = res->end;
> -
> -                       if (start >= (end + 1))
> -                               continue;
> -               }
> -
>                 tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
>                 if (!tmp_res) {
>                         rc = -ENOMEM;
> diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c
> index 1f1d8d8..a5d3ebb 100644
> --- a/drivers/xen/unpopulated-alloc.c
> +++ b/drivers/xen/unpopulated-alloc.c
> @@ -39,6 +39,7 @@ static int fill_list(unsigned int nr_pages)
>         void *vaddr;
>         unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
>         int ret;
> +       struct range mhp_range;
> 
>         res = kzalloc(sizeof(*res), GFP_KERNEL);
>         if (!res)
> @@ -47,8 +48,10 @@ static int fill_list(unsigned int nr_pages)
>         res->name = "Xen scratch";
>         res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
> 
> +       mhp_range = mhp_get_pluggable_range(true);
> +
>         ret = allocate_resource(target_resource, res,
> -                               alloc_pages * PAGE_SIZE, 0, -1,
> +                               alloc_pages * PAGE_SIZE, mhp_range.start,
> mhp_range.end,
>                                 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
>         if (ret < 0) {
>                 pr_err("Cannot allocate new IOMEM resource\n");
> (END)
> 
> I believe, this will work on x86 as arch_get_mappable_range() is not
> implemented there,
> and the default option contains exactly what being used currently (0, -1).
> 
> struct range __weak arch_get_mappable_range(void)
> {
>     struct range mhp_range = {
>         .start = 0UL,
>         .end = -1ULL,
>     };
>     return mhp_range;
> }
> 
> And this is going to be more generic and clear, what do you think?

Yeah this is much better, good thinking!

[-- Attachment #2: Type: text/plain, Size: 176 bytes --]

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 2/4] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT

[Oleksandr]

On 19.11.21 02:32, Stefano Stabellini wrote:

Hi Stefano

> On Thu, 11 Nov 2021, Oleksandr wrote:
>> On 28.10.21 04:28, Stefano Stabellini wrote:
>>
>> Hi Stefano
>>
>> I am sorry for the late response.
>>
>>> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>
>>>> Read the start address of the grant table space from DT
>>>> (region 0).
>>>>
>>>> This patch mostly restores behaviour before commit 3cf4095d7446
>>>> ("arm/xen: Use xen_xlate_map_ballooned_pages to setup grant table")
>>>> but trying not to break the ACPI support added after that commit.
>>>> So the patch touches DT part only and leaves the ACPI part with
>>>> xen_xlate_map_ballooned_pages().
>>>>
>>>> This is a preparation for using Xen extended region feature
>>>> where unused regions of guest physical address space (provided
>>>> by the hypervisor) will be used to create grant/foreign/whatever
>>>> mappings instead of wasting real RAM pages from the domain memory
>>>> for establishing these mappings.
>>>>
>>>> The immediate benefit of this change:
>>>> - Avoid superpage shattering in Xen P2M when establishing
>>>>     stage-2 mapping (GFN <-> MFN) for the grant table space
>>>> - Avoid wasting real RAM pages (reducing the amount of memory
>>>>     usuable) for mapping grant table space
>>>> - The grant table space is always mapped at the exact
>>>>     same place (region 0 is reserved for the grant table)
>>>>
>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>> ---
>>>> Changes RFC -> V2:
>>>>      - new patch
>>>> ---
>>>>    arch/arm/xen/enlighten.c | 32 +++++++++++++++++++++++++-------
>>>>    1 file changed, 25 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
>>>> index 7f1c106b..dea46ec 100644
>>>> --- a/arch/arm/xen/enlighten.c
>>>> +++ b/arch/arm/xen/enlighten.c
>>>> @@ -59,6 +59,9 @@ unsigned long xen_released_pages;
>>>>    struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS]
>>>> __initdata;
>>>>      static __read_mostly unsigned int xen_events_irq;
>>>> +static phys_addr_t xen_grant_frames;
>>> __read_mostly
>> ok
>>
>>
>>>
>>>> +#define GRANT_TABLE_INDEX   0
>>>>      uint32_t xen_start_flags;
>>>>    EXPORT_SYMBOL(xen_start_flags);
>>>> @@ -303,6 +306,7 @@ static void __init xen_acpi_guest_init(void)
>>>>    static void __init xen_dt_guest_init(void)
>>>>    {
>>>>    	struct device_node *xen_node;
>>>> +	struct resource res;
>>>>      	xen_node = of_find_compatible_node(NULL, NULL, "xen,xen");
>>>>    	if (!xen_node) {
>>>> @@ -310,6 +314,12 @@ static void __init xen_dt_guest_init(void)
>>>>    		return;
>>>>    	}
>>>>    +	if (of_address_to_resource(xen_node, GRANT_TABLE_INDEX, &res)) {
>>>> +		pr_err("Xen grant table region is not found\n");
>>>> +		return;
>>>> +	}
>>>> +	xen_grant_frames = res.start;
>>>> +
>>>>    	xen_events_irq = irq_of_parse_and_map(xen_node, 0);
>>>>    }
>>>>    @@ -317,16 +327,20 @@ static int __init xen_guest_init(void)
>>>>    {
>>>>    	struct xen_add_to_physmap xatp;
>>>>    	struct shared_info *shared_info_page = NULL;
>>>> -	int cpu;
>>>> +	int rc, cpu;
>>>>      	if (!xen_domain())
>>>>    		return 0;
>>>>      	if (!acpi_disabled)
>>>>    		xen_acpi_guest_init();
>>>> -	else
>>>> +	else {
>>>>    		xen_dt_guest_init();
>>>>    +		if (!xen_grant_frames)
>>>> +			return -ENODEV;
>>> maybe we can avoid this, see below
>>>
>>>
>>>> +	}
>>>> +
>>>>    	if (!xen_events_irq) {
>>>>    		pr_err("Xen event channel interrupt not found\n");
>>>>    		return -ENODEV;
>>>> @@ -370,12 +384,16 @@ static int __init xen_guest_init(void)
>>>>    	for_each_possible_cpu(cpu)
>>>>    		per_cpu(xen_vcpu_id, cpu) = cpu;
>>>>    -	xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
>>>> -	if (xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
>>>> -					  &xen_auto_xlat_grant_frames.vaddr,
>>>> -					  xen_auto_xlat_grant_frames.count)) {
>>>> +	if (!acpi_disabled) {
>>> To make the code more resilient couldn't we do:
>>>
>>> if (!acpi_disabled || !xen_grant_frames) {
>> I think, we can.
>>
>> On the one hand, indeed the code more resilient and less change.
>>  From the other hand if grant table region is not found then something weird
>> happened as region 0 is always present in reg property if hypervisor node is
>> exposed to the guest.
>> The behavior before commit 3cf4095d7446 ("arm/xen: Use
>> xen_xlate_map_ballooned_pages to setup grant table") was exactly the same in
>> the context of the failure if region wasn't found.
>>
>> ...
>>
>> Well, if we want to make code more resilient, I will update. But, looks like
>> we also need to switch actions in xen_dt_guest_init() in order to process
>> xen_events_irq before xen_grant_frames, otherwise we may return after failing
>> with region and end up not initializing xen_events_irq so xen_guest_init()
>> will fail earlier than reaches that check.
>> What do you think?
>   
> Yes, you are right. I was re-reading the patch to refresh my memory and
> I noticed immediately that xen_dt_guest_init also need to be changed so
> that xen_events_irq is set before xen_grant_frames.
>   
> I think it is a minor change that doesn't add complexity but make the
> code more robust so I think it is a good idea


Great, thank you. Will do in next version.


>
>   
>>>> +		xen_auto_xlat_grant_frames.count = gnttab_max_grant_frames();
>>>> +		rc =
>>>> xen_xlate_map_ballooned_pages(&xen_auto_xlat_grant_frames.pfn,
>>>> +
>>>> &xen_auto_xlat_grant_frames.vaddr,
>>>> +
>>>> xen_auto_xlat_grant_frames.count);
>>>> +	} else
>>>> +		rc = gnttab_setup_auto_xlat_frames(xen_grant_frames);
>>>> +	if (rc) {
>>>>    		free_percpu(xen_vcpu_info);
>>>> -		return -ENOMEM;
>>>> +		return rc;
>>>>    	}
>>>>    	gnttab_init();

-- 
Regards,

Oleksandr Tyshchenko


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 4/4] arm/xen: Read extended regions from DT and init Xen resource

[Oleksandr]

On 19.11.21 03:19, Stefano Stabellini wrote:

Hi Stefano

> On Wed, 10 Nov 2021, Oleksandr wrote:
>> On 28.10.21 04:40, Stefano Stabellini wrote:
>>
>> Hi Stefano
>>
>> I am sorry for the late response.
>>
>>> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>
>>>> This patch implements arch_xen_unpopulated_init() on Arm where
>>>> the extended regions (if any) are gathered from DT and inserted
>>>> into passed Xen resource to be used as unused address space
>>>> for Xen scratch pages by unpopulated-alloc code.
>>>>
>>>> The extended region (safe range) is a region of guest physical
>>>> address space which is unused and could be safely used to create
>>>> grant/foreign mappings instead of wasting real RAM pages from
>>>> the domain memory for establishing these mappings.
>>>>
>>>> The extended regions are chosen by the hypervisor at the domain
>>>> creation time and advertised to it via "reg" property under
>>>> hypervisor node in the guest device-tree. As region 0 is reserved
>>>> for grant table space (always present), the indexes for extended
>>>> regions are 1...N.
>>>>
>>>> If arch_xen_unpopulated_init() fails for some reason the default
>>>> behaviour will be restored (allocate xenballooned pages).
>>>>
>>>> This patch also removes XEN_UNPOPULATED_ALLOC dependency on x86.
>>>>
>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>> ---
>>>> Changes RFC -> V2:
>>>>      - new patch, instead of
>>>>       "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide
>>>> unallocated space"
>>>> ---
>>>>    arch/arm/xen/enlighten.c | 112
>>>> +++++++++++++++++++++++++++++++++++++++++++++++
>>>>    drivers/xen/Kconfig      |   2 +-
>>>>    2 files changed, 113 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
>>>> index dea46ec..1a1e0d3 100644
>>>> --- a/arch/arm/xen/enlighten.c
>>>> +++ b/arch/arm/xen/enlighten.c
>>>> @@ -62,6 +62,7 @@ static __read_mostly unsigned int xen_events_irq;
>>>>    static phys_addr_t xen_grant_frames;
>>>>      #define GRANT_TABLE_INDEX   0
>>>> +#define EXT_REGION_INDEX    1
>>>>      uint32_t xen_start_flags;
>>>>    EXPORT_SYMBOL(xen_start_flags);
>>>> @@ -303,6 +304,117 @@ static void __init xen_acpi_guest_init(void)
>>>>    #endif
>>>>    }
>>>>    +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
>>>> +int arch_xen_unpopulated_init(struct resource *res)
>>>> +{
>>>> +	struct device_node *np;
>>>> +	struct resource *regs, *tmp_res;
>>>> +	uint64_t min_gpaddr = -1, max_gpaddr = 0;
>>>> +	unsigned int i, nr_reg = 0;
>>>> +	struct range mhp_range;
>>>> +	int rc;
>>>> +
>>>> +	if (!xen_domain())
>>>> +		return -ENODEV;
>>>> +
>>>> +	np = of_find_compatible_node(NULL, NULL, "xen,xen");
>>>> +	if (WARN_ON(!np))
>>>> +		return -ENODEV;
>>>> +
>>>> +	/* Skip region 0 which is reserved for grant table space */
>>>> +	while (of_get_address(np, nr_reg + EXT_REGION_INDEX, NULL, NULL))
>>>> +		nr_reg++;
>>>> +	if (!nr_reg) {
>>>> +		pr_err("No extended regions are found\n");
>>>> +		return -EINVAL;
>>>> +	}
>>>> +
>>>> +	regs = kcalloc(nr_reg, sizeof(*regs), GFP_KERNEL);
>>>> +	if (!regs)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	/*
>>>> +	 * Create resource from extended regions provided by the hypervisor to
>>>> be
>>>> +	 * used as unused address space for Xen scratch pages.
>>>> +	 */
>>>> +	for (i = 0; i < nr_reg; i++) {
>>>> +		rc = of_address_to_resource(np, i + EXT_REGION_INDEX,
>>>> &regs[i]);
>>>> +		if (rc)
>>>> +			goto err;
>>>> +
>>>> +		if (max_gpaddr < regs[i].end)
>>>> +			max_gpaddr = regs[i].end;
>>>> +		if (min_gpaddr > regs[i].start)
>>>> +			min_gpaddr = regs[i].start;
>>>> +	}
>>>> +
>>>> +	/* Check whether the resource range is within the hotpluggable range
>>>> */
>>>> +	mhp_range = mhp_get_pluggable_range(true);
>>>> +	if (min_gpaddr < mhp_range.start)
>>>> +		min_gpaddr = mhp_range.start;
>>>> +	if (max_gpaddr > mhp_range.end)
>>>> +		max_gpaddr = mhp_range.end;
>>>> +
>>>> +	res->start = min_gpaddr;
>>>> +	res->end = max_gpaddr;
>>>> +
>>>> +	/*
>>>> +	 * Mark holes between extended regions as unavailable. The rest of
>>>> that
>>>> +	 * address space will be available for the allocation.
>>>> +	 */
>>>> +	for (i = 1; i < nr_reg; i++) {
>>>> +		resource_size_t start, end;
>>>> +
>>>> +		start = regs[i - 1].end + 1;
>>>> +		end = regs[i].start - 1;
>>>> +
>>>> +		if (start > (end + 1)) {
>>> Should this be:
>>>
>>> if (start >= end)
>>>
>>> ?
>> Yes, we can do this here (since the checks are equivalent) but ...
>>
>>>> +			rc = -EINVAL;
>>>> +			goto err;
>>>> +		}
>>>> +
>>>> +		/* There is no hole between regions */
>>>> +		if (start == (end + 1))
>>> Also here, shouldn't it be:
>>>
>>> if (start == end)
>>>
>>> ?
>>     ... not here.
>>
>> As
>>
>> "(start == (end + 1))" is equal to "(regs[i - 1].end + 1 == regs[i].start)"
>>
>> but
>>
>> "(start == end)" is equal to "(regs[i - 1].end + 1 == regs[i].start - 1)"
>   
> OK. But the check:
>
>    if (start >= end)
>
> Actually covers both cases so that's the only check we need?

Sorry, I don't entirely understand the question.
Is the question to use only a single check in that loop?

Paste the updated code which I have locally for the convenience.

  [snip]

     /*
      * Mark holes between extended regions as unavailable. The rest of that
      * address space will be available for the allocation.
      */
     for (i = 1; i < nr_reg; i++) {
         resource_size_t start, end;

         start = regs[i - 1].end + 1;
         end = regs[i].start - 1;

         if (start > (end + 1)) {
             rc = -EINVAL;
             goto err;
         }

         /* There is no hole between regions */
         if (start == (end + 1))
             continue;

         tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
         if (!tmp_res) {
             rc = -ENOMEM;
             goto err;
         }

         tmp_res->name = "Unavailable space";
         tmp_res->start = start;
         tmp_res->end = end;

         rc = insert_resource(&xen_resource, tmp_res);
         if (rc) {
             pr_err("Cannot insert resource %pR (%d)\n", tmp_res, rc);
             kfree(tmp_res);
             goto err;
         }
     }

[snip]


1. The first check is to detect an overlap (which is a wrong 
configuration, correct?) and bail out if true (for example, regX: 
0x81000000...0x82FFFFFF and regY: 0x82000000...0x83FFFFFF).
2. The second check is just to skip current iteration as there is no 
space/hole between regions (for example, regX: 0x81000000...0x82FFFFFF 
and regY: 0x83000000...0x83FFFFFF).
Therefore I think they should be distinguished.

Yes, both check could be transformed to a single one, but this way the 
overlaps will be ignored:
if (start >= (end + 1))
     continue;

Or I really missed something?


>
>
>>> I think I am missing again something in termination accounting :-)
>> If I understand correctly, we need to follow "end = start + size - 1" rule, so
>> the "end" is the last address inside a range, but not the "first" address
>> outside of a range))
> yeah
>   
>
>>>> +			continue;
>>>> +
>>>> +		/* Check whether the hole range is within the resource range
>>>> */
>>>> +		if (start < res->start || end > res->end) {
>>> By definition I don't think this check is necessary as either condition
>>> is impossible?
>>
>> This is a good question, let me please explain.
>> Not all extended regions provided by the hypervisor can be used here. This is
>> because the addressable physical memory range for which the linear mapping
>> could be created has limits on Arm, and maximum addressable range depends on
>> the VA space size (CONFIG_ARM64_VA_BITS_XXX). So we decided to not filter them
>> in hypervisor as this logic could be quite complex as different OS may have
>> different requirement, etc. This means that we need to make sure that regions
>> are within the hotpluggable range to avoid a failure later on when a region is
>> pre-validated by the memory hotplug path.
>>
>> The following code limits the resource range based on that:
>>
>> +    /* Check whether the resource range is within the hotpluggable range */
>> +    mhp_range = mhp_get_pluggable_range(true);
>> +    if (min_gpaddr < mhp_range.start)
>> +        min_gpaddr = mhp_range.start;
>> +    if (max_gpaddr > mhp_range.end)
>> +        max_gpaddr = mhp_range.end;
>> +
>> +    res->start = min_gpaddr;
>> +    res->end = max_gpaddr;
>>
>> In current loop (when calculating and inserting holes) we also need to make
>> sure that resulting hole range is within the resource range (and adjust/skip
>> it if not true) as regs[] used for the calculations contains raw regions as
>> they described in DT so not updated. Otherwise insert_resource() down the
>> function will return an error for the conflicting operations. Yes, I could
>> took a different route and update regs[] in advance to adjust/skip
>> non-suitable regions in front, but I decided to do it on the fly in the loop
>> here, I thought doing it in advance would add some overhead/complexity. What
>> do you think?
> I understand now.
>
>
>> So I am afraid this check is necessary here.
>>
>> For example in my environment the extended regions are:
>>
>> (XEN) Extended region 0: 0->0x8000000
>> (XEN) Extended region 1: 0xc000000->0x30000000
>> (XEN) Extended region 2: 0x40000000->0x47e00000
>> (XEN) Extended region 3: 0xd0000000->0xe6000000
>> (XEN) Extended region 4: 0xe7800000->0xec000000
>> (XEN) Extended region 5: 0xf1200000->0xfd000000
>> (XEN) Extended region 6: 0x100000000->0x500000000
>> (XEN) Extended region 7: 0x580000000->0x600000000
>> (XEN) Extended region 8: 0x680000000->0x700000000
>> (XEN) Extended region 9: 0x780000000->0x10000000000
>>
>> *With* the check the holes are:
>>
>> holes [47e00000 - cfffffff]
>> holes [e6000000 - e77fffff]
>> holes [ec000000 - f11fffff]
>> holes [fd000000 - ffffffff]
>> holes [500000000 - 57fffffff]
>> holes [600000000 - 67fffffff]
>> holes [700000000 - 77fffffff]
>>
>> And they seem to look correct, you can see that two possible holes between
>> extended regions 0-1 (8000000-bffffff) and 1-2 (30000000-3fffffff) were
>> skipped as they entirely located below res->start
>> which is 0x40000000 in my case (48-bit VA: 0x40000000 - 0x80003fffffff).
>>
>> *Without* the check these two holes won't be skipped and as the result
>> insert_resource() will fail.
>>
>>
>> **********
>>
>>
>> I have one idea how we can simplify filter logic, we can drop all checks here
>> (including confusing one) in Arm code and update common code a bit:
>>
>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
>> index 1a1e0d3..ed5b855 100644
>> --- a/arch/arm/xen/enlighten.c
>> +++ b/arch/arm/xen/enlighten.c
>> @@ -311,7 +311,6 @@ int arch_xen_unpopulated_init(struct resource *res)
>>          struct resource *regs, *tmp_res;
>>          uint64_t min_gpaddr = -1, max_gpaddr = 0;
>>          unsigned int i, nr_reg = 0;
>> -       struct range mhp_range;
>>          int rc;
>>
>>          if (!xen_domain())
>> @@ -349,13 +348,6 @@ int arch_xen_unpopulated_init(struct resource *res)
>>                          min_gpaddr = regs[i].start;
>>          }
>>
>> -       /* Check whether the resource range is within the hotpluggable range
>> */
>> -       mhp_range = mhp_get_pluggable_range(true);
>> -       if (min_gpaddr < mhp_range.start)
>> -               min_gpaddr = mhp_range.start;
>> -       if (max_gpaddr > mhp_range.end)
>> -               max_gpaddr = mhp_range.end;
>> -
>>          res->start = min_gpaddr;
>>          res->end = max_gpaddr;
>>
>> @@ -378,17 +370,6 @@ int arch_xen_unpopulated_init(struct resource *res)
>>                  if (start == (end + 1))
>>                          continue;
>>
>> -               /* Check whether the hole range is within the resource range
>> */
>> -               if (start < res->start || end > res->end) {
>> -                       if (start < res->start)
>> -                               start = res->start;
>> -                       if (end > res->end)
>> -                               end = res->end;
>> -
>> -                       if (start >= (end + 1))
>> -                               continue;
>> -               }
>> -
>>                  tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
>>                  if (!tmp_res) {
>>                          rc = -ENOMEM;
>> diff --git a/drivers/xen/unpopulated-alloc.c b/drivers/xen/unpopulated-alloc.c
>> index 1f1d8d8..a5d3ebb 100644
>> --- a/drivers/xen/unpopulated-alloc.c
>> +++ b/drivers/xen/unpopulated-alloc.c
>> @@ -39,6 +39,7 @@ static int fill_list(unsigned int nr_pages)
>>          void *vaddr;
>>          unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
>>          int ret;
>> +       struct range mhp_range;
>>
>>          res = kzalloc(sizeof(*res), GFP_KERNEL);
>>          if (!res)
>> @@ -47,8 +48,10 @@ static int fill_list(unsigned int nr_pages)
>>          res->name = "Xen scratch";
>>          res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
>>
>> +       mhp_range = mhp_get_pluggable_range(true);
>> +
>>          ret = allocate_resource(target_resource, res,
>> -                               alloc_pages * PAGE_SIZE, 0, -1,
>> +                               alloc_pages * PAGE_SIZE, mhp_range.start,
>> mhp_range.end,
>>                                  PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
>>          if (ret < 0) {
>>                  pr_err("Cannot allocate new IOMEM resource\n");
>> (END)
>>
>> I believe, this will work on x86 as arch_get_mappable_range() is not
>> implemented there,
>> and the default option contains exactly what being used currently (0, -1).
>>
>> struct range __weak arch_get_mappable_range(void)
>> {
>>      struct range mhp_range = {
>>          .start = 0UL,
>>          .end = -1ULL,
>>      };
>>      return mhp_range;
>> }
>>
>> And this is going to be more generic and clear, what do you think?
> Yeah this is much better, good thinking!

Great, thank you. Will do in next version.


-- 
Regards,

Oleksandr Tyshchenko


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 4/4] arm/xen: Read extended regions from DT and init Xen resource

[Stefano Stabellini]

[-- Attachment #1: Type: text/plain, Size: 8464 bytes --]

On Fri, 19 Nov 2021, Oleksandr wrote:
> On 19.11.21 03:19, Stefano Stabellini wrote:
> > On Wed, 10 Nov 2021, Oleksandr wrote:
> > > On 28.10.21 04:40, Stefano Stabellini wrote:
> > > 
> > > Hi Stefano
> > > 
> > > I am sorry for the late response.
> > > 
> > > > On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
> > > > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > > > 
> > > > > This patch implements arch_xen_unpopulated_init() on Arm where
> > > > > the extended regions (if any) are gathered from DT and inserted
> > > > > into passed Xen resource to be used as unused address space
> > > > > for Xen scratch pages by unpopulated-alloc code.
> > > > > 
> > > > > The extended region (safe range) is a region of guest physical
> > > > > address space which is unused and could be safely used to create
> > > > > grant/foreign mappings instead of wasting real RAM pages from
> > > > > the domain memory for establishing these mappings.
> > > > > 
> > > > > The extended regions are chosen by the hypervisor at the domain
> > > > > creation time and advertised to it via "reg" property under
> > > > > hypervisor node in the guest device-tree. As region 0 is reserved
> > > > > for grant table space (always present), the indexes for extended
> > > > > regions are 1...N.
> > > > > 
> > > > > If arch_xen_unpopulated_init() fails for some reason the default
> > > > > behaviour will be restored (allocate xenballooned pages).
> > > > > 
> > > > > This patch also removes XEN_UNPOPULATED_ALLOC dependency on x86.
> > > > > 
> > > > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > > > ---
> > > > > Changes RFC -> V2:
> > > > >      - new patch, instead of
> > > > >       "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to
> > > > > provide
> > > > > unallocated space"
> > > > > ---
> > > > >    arch/arm/xen/enlighten.c | 112
> > > > > +++++++++++++++++++++++++++++++++++++++++++++++
> > > > >    drivers/xen/Kconfig      |   2 +-
> > > > >    2 files changed, 113 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > > > > index dea46ec..1a1e0d3 100644
> > > > > --- a/arch/arm/xen/enlighten.c
> > > > > +++ b/arch/arm/xen/enlighten.c
> > > > > @@ -62,6 +62,7 @@ static __read_mostly unsigned int xen_events_irq;
> > > > >    static phys_addr_t xen_grant_frames;
> > > > >      #define GRANT_TABLE_INDEX   0
> > > > > +#define EXT_REGION_INDEX    1
> > > > >      uint32_t xen_start_flags;
> > > > >    EXPORT_SYMBOL(xen_start_flags);
> > > > > @@ -303,6 +304,117 @@ static void __init xen_acpi_guest_init(void)
> > > > >    #endif
> > > > >    }
> > > > >    +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
> > > > > +int arch_xen_unpopulated_init(struct resource *res)
> > > > > +{
> > > > > +	struct device_node *np;
> > > > > +	struct resource *regs, *tmp_res;
> > > > > +	uint64_t min_gpaddr = -1, max_gpaddr = 0;
> > > > > +	unsigned int i, nr_reg = 0;
> > > > > +	struct range mhp_range;
> > > > > +	int rc;
> > > > > +
> > > > > +	if (!xen_domain())
> > > > > +		return -ENODEV;
> > > > > +
> > > > > +	np = of_find_compatible_node(NULL, NULL, "xen,xen");
> > > > > +	if (WARN_ON(!np))
> > > > > +		return -ENODEV;
> > > > > +
> > > > > +	/* Skip region 0 which is reserved for grant table space */
> > > > > +	while (of_get_address(np, nr_reg + EXT_REGION_INDEX, NULL,
> > > > > NULL))
> > > > > +		nr_reg++;
> > > > > +	if (!nr_reg) {
> > > > > +		pr_err("No extended regions are found\n");
> > > > > +		return -EINVAL;
> > > > > +	}
> > > > > +
> > > > > +	regs = kcalloc(nr_reg, sizeof(*regs), GFP_KERNEL);
> > > > > +	if (!regs)
> > > > > +		return -ENOMEM;
> > > > > +
> > > > > +	/*
> > > > > +	 * Create resource from extended regions provided by the
> > > > > hypervisor to
> > > > > be
> > > > > +	 * used as unused address space for Xen scratch pages.
> > > > > +	 */
> > > > > +	for (i = 0; i < nr_reg; i++) {
> > > > > +		rc = of_address_to_resource(np, i + EXT_REGION_INDEX,
> > > > > &regs[i]);
> > > > > +		if (rc)
> > > > > +			goto err;
> > > > > +
> > > > > +		if (max_gpaddr < regs[i].end)
> > > > > +			max_gpaddr = regs[i].end;
> > > > > +		if (min_gpaddr > regs[i].start)
> > > > > +			min_gpaddr = regs[i].start;
> > > > > +	}
> > > > > +
> > > > > +	/* Check whether the resource range is within the hotpluggable
> > > > > range
> > > > > */
> > > > > +	mhp_range = mhp_get_pluggable_range(true);
> > > > > +	if (min_gpaddr < mhp_range.start)
> > > > > +		min_gpaddr = mhp_range.start;
> > > > > +	if (max_gpaddr > mhp_range.end)
> > > > > +		max_gpaddr = mhp_range.end;
> > > > > +
> > > > > +	res->start = min_gpaddr;
> > > > > +	res->end = max_gpaddr;
> > > > > +
> > > > > +	/*
> > > > > +	 * Mark holes between extended regions as unavailable. The
> > > > > rest of
> > > > > that
> > > > > +	 * address space will be available for the allocation.
> > > > > +	 */
> > > > > +	for (i = 1; i < nr_reg; i++) {
> > > > > +		resource_size_t start, end;
> > > > > +
> > > > > +		start = regs[i - 1].end + 1;
> > > > > +		end = regs[i].start - 1;
> > > > > +
> > > > > +		if (start > (end + 1)) {
> > > > Should this be:
> > > > 
> > > > if (start >= end)
> > > > 
> > > > ?
> > > Yes, we can do this here (since the checks are equivalent) but ...
> > > 
> > > > > +			rc = -EINVAL;
> > > > > +			goto err;
> > > > > +		}
> > > > > +
> > > > > +		/* There is no hole between regions */
> > > > > +		if (start == (end + 1))
> > > > Also here, shouldn't it be:
> > > > 
> > > > if (start == end)
> > > > 
> > > > ?
> > >     ... not here.
> > > 
> > > As
> > > 
> > > "(start == (end + 1))" is equal to "(regs[i - 1].end + 1 ==
> > > regs[i].start)"
> > > 
> > > but
> > > 
> > > "(start == end)" is equal to "(regs[i - 1].end + 1 == regs[i].start - 1)"
> >   OK. But the check:
> > 
> >    if (start >= end)
> > 
> > Actually covers both cases so that's the only check we need?
> 
> Sorry, I don't entirely understand the question.
> Is the question to use only a single check in that loop?
> 
> Paste the updated code which I have locally for the convenience.
> 
>  [snip]
> 
>     /*
>      * Mark holes between extended regions as unavailable. The rest of that
>      * address space will be available for the allocation.
>      */
>     for (i = 1; i < nr_reg; i++) {
>         resource_size_t start, end;
> 
>         start = regs[i - 1].end + 1;
>         end = regs[i].start - 1;
> 
>         if (start > (end + 1)) {
>             rc = -EINVAL;
>             goto err;
>         }
> 
>         /* There is no hole between regions */
>         if (start == (end + 1))
>             continue;
> 
>         tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
>         if (!tmp_res) {
>             rc = -ENOMEM;
>             goto err;
>         }
> 
>         tmp_res->name = "Unavailable space";
>         tmp_res->start = start;
>         tmp_res->end = end;
> 
>         rc = insert_resource(&xen_resource, tmp_res);
>         if (rc) {
>             pr_err("Cannot insert resource %pR (%d)\n", tmp_res, rc);
>             kfree(tmp_res);
>             goto err;
>         }
>     }
> 
> [snip]
> 
> 
> 1. The first check is to detect an overlap (which is a wrong configuration,
> correct?) and bail out if true (for example, regX: 0x81000000...0x82FFFFFF and
> regY: 0x82000000...0x83FFFFFF).
> 2. The second check is just to skip current iteration as there is no
> space/hole between regions (for example, regX: 0x81000000...0x82FFFFFF and
> regY: 0x83000000...0x83FFFFFF).
> Therefore I think they should be distinguished.
> 
> Yes, both check could be transformed to a single one, but this way the
> overlaps will be ignored:
> if (start >= (end + 1))
>     continue;
> 
> Or I really missed something?

You are right it is better to distinguish the two cases. I suggest the
code below because I think it is a clearer, even if it might be slightly
less efficient. I don't feel too strongly about it though.

		resource_size_t start, end;

		/* There is no hole between regions */
		if ( regs[i - 1].end + 1 == regs[i].start )
			continue;

		if ( regs[i - 1].end + 1 > regs[i].start) {
			rc = -EINVAL;
			goto err;
		}

		start = regs[i - 1].end + 1;
		end = regs[i].start - 1;

[-- Attachment #2: Type: text/plain, Size: 176 bytes --]

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH V2 4/4] arm/xen: Read extended regions from DT and init Xen resource

[Oleksandr]

On 20.11.21 04:36, Stefano Stabellini wrote:


Hi Stefano

> On Fri, 19 Nov 2021, Oleksandr wrote:
>> On 19.11.21 03:19, Stefano Stabellini wrote:
>>> On Wed, 10 Nov 2021, Oleksandr wrote:
>>>> On 28.10.21 04:40, Stefano Stabellini wrote:
>>>>
>>>> Hi Stefano
>>>>
>>>> I am sorry for the late response.
>>>>
>>>>> On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
>>>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>>>
>>>>>> This patch implements arch_xen_unpopulated_init() on Arm where
>>>>>> the extended regions (if any) are gathered from DT and inserted
>>>>>> into passed Xen resource to be used as unused address space
>>>>>> for Xen scratch pages by unpopulated-alloc code.
>>>>>>
>>>>>> The extended region (safe range) is a region of guest physical
>>>>>> address space which is unused and could be safely used to create
>>>>>> grant/foreign mappings instead of wasting real RAM pages from
>>>>>> the domain memory for establishing these mappings.
>>>>>>
>>>>>> The extended regions are chosen by the hypervisor at the domain
>>>>>> creation time and advertised to it via "reg" property under
>>>>>> hypervisor node in the guest device-tree. As region 0 is reserved
>>>>>> for grant table space (always present), the indexes for extended
>>>>>> regions are 1...N.
>>>>>>
>>>>>> If arch_xen_unpopulated_init() fails for some reason the default
>>>>>> behaviour will be restored (allocate xenballooned pages).
>>>>>>
>>>>>> This patch also removes XEN_UNPOPULATED_ALLOC dependency on x86.
>>>>>>
>>>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>>> ---
>>>>>> Changes RFC -> V2:
>>>>>>       - new patch, instead of
>>>>>>        "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to
>>>>>> provide
>>>>>> unallocated space"
>>>>>> ---
>>>>>>     arch/arm/xen/enlighten.c | 112
>>>>>> +++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>     drivers/xen/Kconfig      |   2 +-
>>>>>>     2 files changed, 113 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
>>>>>> index dea46ec..1a1e0d3 100644
>>>>>> --- a/arch/arm/xen/enlighten.c
>>>>>> +++ b/arch/arm/xen/enlighten.c
>>>>>> @@ -62,6 +62,7 @@ static __read_mostly unsigned int xen_events_irq;
>>>>>>     static phys_addr_t xen_grant_frames;
>>>>>>       #define GRANT_TABLE_INDEX   0
>>>>>> +#define EXT_REGION_INDEX    1
>>>>>>       uint32_t xen_start_flags;
>>>>>>     EXPORT_SYMBOL(xen_start_flags);
>>>>>> @@ -303,6 +304,117 @@ static void __init xen_acpi_guest_init(void)
>>>>>>     #endif
>>>>>>     }
>>>>>>     +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
>>>>>> +int arch_xen_unpopulated_init(struct resource *res)
>>>>>> +{
>>>>>> +	struct device_node *np;
>>>>>> +	struct resource *regs, *tmp_res;
>>>>>> +	uint64_t min_gpaddr = -1, max_gpaddr = 0;
>>>>>> +	unsigned int i, nr_reg = 0;
>>>>>> +	struct range mhp_range;
>>>>>> +	int rc;
>>>>>> +
>>>>>> +	if (!xen_domain())
>>>>>> +		return -ENODEV;
>>>>>> +
>>>>>> +	np = of_find_compatible_node(NULL, NULL, "xen,xen");
>>>>>> +	if (WARN_ON(!np))
>>>>>> +		return -ENODEV;
>>>>>> +
>>>>>> +	/* Skip region 0 which is reserved for grant table space */
>>>>>> +	while (of_get_address(np, nr_reg + EXT_REGION_INDEX, NULL,
>>>>>> NULL))
>>>>>> +		nr_reg++;
>>>>>> +	if (!nr_reg) {
>>>>>> +		pr_err("No extended regions are found\n");
>>>>>> +		return -EINVAL;
>>>>>> +	}
>>>>>> +
>>>>>> +	regs = kcalloc(nr_reg, sizeof(*regs), GFP_KERNEL);
>>>>>> +	if (!regs)
>>>>>> +		return -ENOMEM;
>>>>>> +
>>>>>> +	/*
>>>>>> +	 * Create resource from extended regions provided by the
>>>>>> hypervisor to
>>>>>> be
>>>>>> +	 * used as unused address space for Xen scratch pages.
>>>>>> +	 */
>>>>>> +	for (i = 0; i < nr_reg; i++) {
>>>>>> +		rc = of_address_to_resource(np, i + EXT_REGION_INDEX,
>>>>>> &regs[i]);
>>>>>> +		if (rc)
>>>>>> +			goto err;
>>>>>> +
>>>>>> +		if (max_gpaddr < regs[i].end)
>>>>>> +			max_gpaddr = regs[i].end;
>>>>>> +		if (min_gpaddr > regs[i].start)
>>>>>> +			min_gpaddr = regs[i].start;
>>>>>> +	}
>>>>>> +
>>>>>> +	/* Check whether the resource range is within the hotpluggable
>>>>>> range
>>>>>> */
>>>>>> +	mhp_range = mhp_get_pluggable_range(true);
>>>>>> +	if (min_gpaddr < mhp_range.start)
>>>>>> +		min_gpaddr = mhp_range.start;
>>>>>> +	if (max_gpaddr > mhp_range.end)
>>>>>> +		max_gpaddr = mhp_range.end;
>>>>>> +
>>>>>> +	res->start = min_gpaddr;
>>>>>> +	res->end = max_gpaddr;
>>>>>> +
>>>>>> +	/*
>>>>>> +	 * Mark holes between extended regions as unavailable. The
>>>>>> rest of
>>>>>> that
>>>>>> +	 * address space will be available for the allocation.
>>>>>> +	 */
>>>>>> +	for (i = 1; i < nr_reg; i++) {
>>>>>> +		resource_size_t start, end;
>>>>>> +
>>>>>> +		start = regs[i - 1].end + 1;
>>>>>> +		end = regs[i].start - 1;
>>>>>> +
>>>>>> +		if (start > (end + 1)) {
>>>>> Should this be:
>>>>>
>>>>> if (start >= end)
>>>>>
>>>>> ?
>>>> Yes, we can do this here (since the checks are equivalent) but ...
>>>>
>>>>>> +			rc = -EINVAL;
>>>>>> +			goto err;
>>>>>> +		}
>>>>>> +
>>>>>> +		/* There is no hole between regions */
>>>>>> +		if (start == (end + 1))
>>>>> Also here, shouldn't it be:
>>>>>
>>>>> if (start == end)
>>>>>
>>>>> ?
>>>>      ... not here.
>>>>
>>>> As
>>>>
>>>> "(start == (end + 1))" is equal to "(regs[i - 1].end + 1 ==
>>>> regs[i].start)"
>>>>
>>>> but
>>>>
>>>> "(start == end)" is equal to "(regs[i - 1].end + 1 == regs[i].start - 1)"
>>>    OK. But the check:
>>>
>>>     if (start >= end)
>>>
>>> Actually covers both cases so that's the only check we need?
>> Sorry, I don't entirely understand the question.
>> Is the question to use only a single check in that loop?
>>
>> Paste the updated code which I have locally for the convenience.
>>
>>   [snip]
>>
>>      /*
>>       * Mark holes between extended regions as unavailable. The rest of that
>>       * address space will be available for the allocation.
>>       */
>>      for (i = 1; i < nr_reg; i++) {
>>          resource_size_t start, end;
>>
>>          start = regs[i - 1].end + 1;
>>          end = regs[i].start - 1;
>>
>>          if (start > (end + 1)) {
>>              rc = -EINVAL;
>>              goto err;
>>          }
>>
>>          /* There is no hole between regions */
>>          if (start == (end + 1))
>>              continue;
>>
>>          tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
>>          if (!tmp_res) {
>>              rc = -ENOMEM;
>>              goto err;
>>          }
>>
>>          tmp_res->name = "Unavailable space";
>>          tmp_res->start = start;
>>          tmp_res->end = end;
>>
>>          rc = insert_resource(&xen_resource, tmp_res);
>>          if (rc) {
>>              pr_err("Cannot insert resource %pR (%d)\n", tmp_res, rc);
>>              kfree(tmp_res);
>>              goto err;
>>          }
>>      }
>>
>> [snip]
>>
>>
>> 1. The first check is to detect an overlap (which is a wrong configuration,
>> correct?) and bail out if true (for example, regX: 0x81000000...0x82FFFFFF and
>> regY: 0x82000000...0x83FFFFFF).
>> 2. The second check is just to skip current iteration as there is no
>> space/hole between regions (for example, regX: 0x81000000...0x82FFFFFF and
>> regY: 0x83000000...0x83FFFFFF).
>> Therefore I think they should be distinguished.
>>
>> Yes, both check could be transformed to a single one, but this way the
>> overlaps will be ignored:
>> if (start >= (end + 1))
>>      continue;
>>
>> Or I really missed something?
> You are right it is better to distinguish the two cases. I suggest the
> code below because I think it is a clearer, even if it might be slightly
> less efficient. I don't feel too strongly about it though.
>
> 		resource_size_t start, end;
>
> 		/* There is no hole between regions */
> 		if ( regs[i - 1].end + 1 == regs[i].start )
> 			continue;
>
> 		if ( regs[i - 1].end + 1 > regs[i].start) {
> 			rc = -EINVAL;
> 			goto err;
> 		}
>
> 		start = regs[i - 1].end + 1;
> 		end = regs[i].start - 1;

OK, let's make code clearer, will do.


-- 
Regards,

Oleksandr Tyshchenko


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel