[PATCH v3 0/8] arm64: Default to 32-bit wide ZONE_DMA

[PATCH v3 0/8] arm64: Default to 32-bit wide ZONE_DMA

[Nicolas Saenz Julienne]

Using two distinct DMA zones turned out to be problematic. Here's an
attempt go back to a saner default.

I tested this on both a RPi4 and QEMU.

---

Changes since v2:
 - Introduce Ard's patch
 - Improve OF dma-ranges parsing function
 - Add unit test for OF function
 - Address small changes
 - Move crashkernel reservation later in boot process

Changes since v1:
 - Parse dma-ranges instead of using machine compatible string

Ard Biesheuvel (1):
  arm64: mm: Set ZONE_DMA size based on early IORT scan

Nicolas Saenz Julienne (7):
  arm64: mm: Move reserve_crashkernel() into mem_init()
  arm64: mm: Move zone_dma_bits initialization into zone_sizes_init()
  of/address: Introduce of_dma_get_max_cpu_address()
  of: unittest: Add test for of_dma_get_max_cpu_address()
  dma-direct: Turn zone_dma_bits default value into a define
  arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges
  mm: Update DMA zones description

 arch/arm64/include/asm/processor.h |  1 +
 arch/arm64/mm/init.c               | 20 ++++++------
 drivers/acpi/arm64/iort.c          | 51 ++++++++++++++++++++++++++++++
 drivers/of/address.c               | 42 ++++++++++++++++++++++++
 drivers/of/unittest.c              | 20 ++++++++++++
 include/linux/acpi_iort.h          |  4 +++
 include/linux/dma-direct.h         |  3 ++
 include/linux/mmzone.h             |  5 +--
 include/linux/of.h                 |  7 ++++
 kernel/dma/direct.c                |  2 +-
 10 files changed, 143 insertions(+), 12 deletions(-)

-- 
2.28.0

[PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Nicolas Saenz Julienne]

From: Ard Biesheuvel <ardb@kernel.org>

We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
incorporating masters that can address less than 32 bits of DMA, in
particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
peripherals that can only address up to 1 GB (and its PCIe host
bridge can only access the bottom 3 GB)

Instructing the DMA layer about these limitations is straight-forward,
even though we had to fix some issues regarding memory limits set in
the IORT for named components, and regarding the handling of ACPI _DMA
methods. However, the DMA layer also needs to be able to allocate
memory that is guaranteed to meet those DMA constraints, for bounce
buffering as well as allocating the backing for consistent mappings.

This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
problems with kdump, and potentially in other places where allocations
cannot cross zone boundaries. Therefore, we should avoid having two
separate DMA zones when possible.

So let's do an early scan of the IORT, and only create the ZONE_DMA
if we encounter any devices that need it. This puts the burden on
the firmware to describe such limitations in the IORT, which may be
redundant (and less precise) if _DMA methods are also being provided.
However, it should be noted that this situation is highly unusual for
arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
the _DMA method if implemented, and so we will not lose the ability to
perform streaming DMA outside the ZONE_DMA if the _DMA method permits
it.

Cc: Jeremy Linton <jeremy.linton@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
[nsaenz: Rebased, removed documentation change, warnings and add
declaration in acpi_iort.h]
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---
 arch/arm64/mm/init.c      |  6 +++++
 drivers/acpi/arm64/iort.c | 51 +++++++++++++++++++++++++++++++++++++++
 include/linux/acpi_iort.h |  4 +++
 3 files changed, 61 insertions(+)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 97b0d2768349..f321761eedb2 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -29,6 +29,7 @@
 #include <linux/kexec.h>
 #include <linux/crash_dump.h>
 #include <linux/hugetlb.h>
+#include <linux/acpi_iort.h>
 
 #include <asm/boot.h>
 #include <asm/fixmap.h>
@@ -196,6 +197,11 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 #ifdef CONFIG_ZONE_DMA
 	zone_dma_bits = min(zone_dma_bits,
 			    (unsigned int)ilog2(of_dma_get_max_cpu_address(NULL)));
+
+	if (IS_ENABLED(CONFIG_ACPI))
+		zone_dma_bits = min(zone_dma_bits,
+				    acpi_iort_get_zone_dma_size());
+
 	arm64_dma_phys_limit = max_zone_phys(zone_dma_bits);
 	max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
 #endif
diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
index 9929ff50c0c0..8f530bf3c03b 100644
--- a/drivers/acpi/arm64/iort.c
+++ b/drivers/acpi/arm64/iort.c
@@ -1718,3 +1718,54 @@ void __init acpi_iort_init(void)
 
 	iort_init_platform_devices();
 }
+
+#ifdef CONFIG_ZONE_DMA
+/*
+ * Check the IORT whether any devices exist whose DMA mask is < 32 bits.
+ * If so, return the smallest value encountered, or 32 otherwise.
+ */
+unsigned int __init acpi_iort_get_zone_dma_size(void)
+{
+	struct acpi_table_iort *iort;
+	struct acpi_iort_node *node, *end;
+	acpi_status status;
+	u8 limit = 32;
+	int i;
+
+	if (acpi_disabled)
+		return limit;
+
+	status = acpi_get_table(ACPI_SIG_IORT, 0,
+				(struct acpi_table_header **)&iort);
+	if (ACPI_FAILURE(status))
+		return limit;
+
+	node = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->node_offset);
+	end = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->header.length);
+
+	for (i = 0; i < iort->node_count; i++) {
+		if (node >= end)
+			break;
+
+		switch (node->type) {
+			struct acpi_iort_named_component *ncomp;
+			struct acpi_iort_root_complex *rc;
+
+		case ACPI_IORT_NODE_NAMED_COMPONENT:
+			ncomp = (struct acpi_iort_named_component *)node->node_data;
+			if (ncomp->memory_address_limit)
+				limit = min(limit, ncomp->memory_address_limit);
+			break;
+
+		case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
+			rc = (struct acpi_iort_root_complex *)node->node_data;
+			if (rc->memory_address_limit)
+				limit = min(limit, rc->memory_address_limit);
+			break;
+		}
+		node = ACPI_ADD_PTR(struct acpi_iort_node, node, node->length);
+	}
+	acpi_put_table(&iort->header);
+	return limit;
+}
+#endif
diff --git a/include/linux/acpi_iort.h b/include/linux/acpi_iort.h
index 20a32120bb88..7d2e184f0d4d 100644
--- a/include/linux/acpi_iort.h
+++ b/include/linux/acpi_iort.h
@@ -38,6 +38,7 @@ void iort_dma_setup(struct device *dev, u64 *dma_addr, u64 *size);
 const struct iommu_ops *iort_iommu_configure_id(struct device *dev,
 						const u32 *id_in);
 int iort_iommu_msi_get_resv_regions(struct device *dev, struct list_head *head);
+unsigned int acpi_iort_get_zone_dma_size(void);
 #else
 static inline void acpi_iort_init(void) { }
 static inline u32 iort_msi_map_id(struct device *dev, u32 id)
@@ -55,6 +56,9 @@ static inline const struct iommu_ops *iort_iommu_configure_id(
 static inline
 int iort_iommu_msi_get_resv_regions(struct device *dev, struct list_head *head)
 { return 0; }
+
+static inline unsigned int acpi_iort_get_zone_dma_size(void)
+{ return 32; }
 #endif
 
 #endif /* __ACPI_IORT_H__ */
-- 
2.28.0

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Lorenzo Pieralisi]

On Wed, Oct 14, 2020 at 09:12:09PM +0200, Nicolas Saenz Julienne wrote:

[...]

> +unsigned int __init acpi_iort_get_zone_dma_size(void)
> +{
> +	struct acpi_table_iort *iort;
> +	struct acpi_iort_node *node, *end;
> +	acpi_status status;
> +	u8 limit = 32;
> +	int i;
> +
> +	if (acpi_disabled)
> +		return limit;
> +
> +	status = acpi_get_table(ACPI_SIG_IORT, 0,
> +				(struct acpi_table_header **)&iort);
> +	if (ACPI_FAILURE(status))
> +		return limit;
> +
> +	node = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->node_offset);
> +	end = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->header.length);
> +
> +	for (i = 0; i < iort->node_count; i++) {
> +		if (node >= end)
> +			break;
> +
> +		switch (node->type) {
> +			struct acpi_iort_named_component *ncomp;
> +			struct acpi_iort_root_complex *rc;
> +
> +		case ACPI_IORT_NODE_NAMED_COMPONENT:
> +			ncomp = (struct acpi_iort_named_component *)node->node_data;
> +			if (ncomp->memory_address_limit)
> +				limit = min(limit, ncomp->memory_address_limit);
> +			break;
> +
> +		case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
> +			rc = (struct acpi_iort_root_complex *)node->node_data;
> +			if (rc->memory_address_limit)

You need to add a node revision check here, see rc_dma_get_range() in
drivers/acpi/arm64/iort.c, otherwise we may be reading junk data
in older IORT tables - acpica structures are always referring to the
latest specs.

Thanks,
Lorenzo

> +				limit = min(limit, rc->memory_address_limit);
> +			break;
> +		}
> +		node = ACPI_ADD_PTR(struct acpi_iort_node, node, node->length);
> +	}
> +	acpi_put_table(&iort->header);
> +	return limit;
> +}
> +#endif
> diff --git a/include/linux/acpi_iort.h b/include/linux/acpi_iort.h
> index 20a32120bb88..7d2e184f0d4d 100644
> --- a/include/linux/acpi_iort.h
> +++ b/include/linux/acpi_iort.h
> @@ -38,6 +38,7 @@ void iort_dma_setup(struct device *dev, u64 *dma_addr, u64 *size);
>  const struct iommu_ops *iort_iommu_configure_id(struct device *dev,
>  						const u32 *id_in);
>  int iort_iommu_msi_get_resv_regions(struct device *dev, struct list_head *head);
> +unsigned int acpi_iort_get_zone_dma_size(void);
>  #else
>  static inline void acpi_iort_init(void) { }
>  static inline u32 iort_msi_map_id(struct device *dev, u32 id)
> @@ -55,6 +56,9 @@ static inline const struct iommu_ops *iort_iommu_configure_id(
>  static inline
>  int iort_iommu_msi_get_resv_regions(struct device *dev, struct list_head *head)
>  { return 0; }
> +
> +static inline unsigned int acpi_iort_get_zone_dma_size(void)
> +{ return 32; }
>  #endif
>  
>  #endif /* __ACPI_IORT_H__ */
> -- 
> 2.28.0
> 

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Hanjun Guo]

On 2020/10/15 3:12, Nicolas Saenz Julienne wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
> incorporating masters that can address less than 32 bits of DMA, in
> particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
> peripherals that can only address up to 1 GB (and its PCIe host
> bridge can only access the bottom 3 GB)
> 
> Instructing the DMA layer about these limitations is straight-forward,
> even though we had to fix some issues regarding memory limits set in
> the IORT for named components, and regarding the handling of ACPI _DMA
> methods. However, the DMA layer also needs to be able to allocate
> memory that is guaranteed to meet those DMA constraints, for bounce
> buffering as well as allocating the backing for consistent mappings.
> 
> This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
> it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
> problems with kdump, and potentially in other places where allocations
> cannot cross zone boundaries. Therefore, we should avoid having two
> separate DMA zones when possible.
> 
> So let's do an early scan of the IORT, and only create the ZONE_DMA
> if we encounter any devices that need it. This puts the burden on
> the firmware to describe such limitations in the IORT, which may be
> redundant (and less precise) if _DMA methods are also being provided.
> However, it should be noted that this situation is highly unusual for
> arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
> the _DMA method if implemented, and so we will not lose the ability to
> perform streaming DMA outside the ZONE_DMA if the _DMA method permits
> it.

Sorry, I'm still a little bit confused. With this patch, if we have
a device which set the right _DMA method (DMA size >= 32), but with the
wrong DMA size in IORT, we still have the ZONE_DMA created which
is actually not needed?

> 
> Cc: Jeremy Linton <jeremy.linton@arm.com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Hanjun Guo <guohanjun@huawei.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> [nsaenz: Rebased, removed documentation change, warnings and add
> declaration in acpi_iort.h]
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> ---
>   arch/arm64/mm/init.c      |  6 +++++
>   drivers/acpi/arm64/iort.c | 51 +++++++++++++++++++++++++++++++++++++++
>   include/linux/acpi_iort.h |  4 +++
>   3 files changed, 61 insertions(+)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 97b0d2768349..f321761eedb2 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -29,6 +29,7 @@
>   #include <linux/kexec.h>
>   #include <linux/crash_dump.h>
>   #include <linux/hugetlb.h>
> +#include <linux/acpi_iort.h>
>   
>   #include <asm/boot.h>
>   #include <asm/fixmap.h>
> @@ -196,6 +197,11 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
>   #ifdef CONFIG_ZONE_DMA
>   	zone_dma_bits = min(zone_dma_bits,
>   			    (unsigned int)ilog2(of_dma_get_max_cpu_address(NULL)));
> +
> +	if (IS_ENABLED(CONFIG_ACPI))
> +		zone_dma_bits = min(zone_dma_bits,
> +				    acpi_iort_get_zone_dma_size());
> +
>   	arm64_dma_phys_limit = max_zone_phys(zone_dma_bits);
>   	max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
>   #endif
> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index 9929ff50c0c0..8f530bf3c03b 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -1718,3 +1718,54 @@ void __init acpi_iort_init(void)
>   
>   	iort_init_platform_devices();
>   }
> +
> +#ifdef CONFIG_ZONE_DMA
> +/*
> + * Check the IORT whether any devices exist whose DMA mask is < 32 bits.
> + * If so, return the smallest value encountered, or 32 otherwise.
> + */
> +unsigned int __init acpi_iort_get_zone_dma_size(void)
> +{
> +	struct acpi_table_iort *iort;
> +	struct acpi_iort_node *node, *end;
> +	acpi_status status;
> +	u8 limit = 32;
> +	int i;
> +
> +	if (acpi_disabled)
> +		return limit;
> +
> +	status = acpi_get_table(ACPI_SIG_IORT, 0,
> +				(struct acpi_table_header **)&iort);
> +	if (ACPI_FAILURE(status))
> +		return limit;
> +
> +	node = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->node_offset);
> +	end = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->header.length);
> +
> +	for (i = 0; i < iort->node_count; i++) {
> +		if (node >= end)
> +			break;
> +
> +		switch (node->type) {
> +			struct acpi_iort_named_component *ncomp;
> +			struct acpi_iort_root_complex *rc;
> +
> +		case ACPI_IORT_NODE_NAMED_COMPONENT:
> +			ncomp = (struct acpi_iort_named_component *)node->node_data;
> +			if (ncomp->memory_address_limit)
> +				limit = min(limit, ncomp->memory_address_limit);
> +			break;
> +
> +		case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
> +			rc = (struct acpi_iort_root_complex *)node->node_data;
> +			if (rc->memory_address_limit)
> +				limit = min(limit, rc->memory_address_limit);

There is no "Memory address size limit" field in revision 0 table, so as
Lorenzo reminded, please add a revision check here.

Thanks
Hanjun


> +			break;
> +		}
> +		node = ACPI_ADD_PTR(struct acpi_iort_node, node, node->length);
> +	}
> +	acpi_put_table(&iort->header);
> +	return limit;
> +}
> +#endif
> diff --git a/include/linux/acpi_iort.h b/include/linux/acpi_iort.h
> index 20a32120bb88..7d2e184f0d4d 100644
> --- a/include/linux/acpi_iort.h
> +++ b/include/linux/acpi_iort.h
> @@ -38,6 +38,7 @@ void iort_dma_setup(struct device *dev, u64 *dma_addr, u64 *size);
>   const struct iommu_ops *iort_iommu_configure_id(struct device *dev,
>   						const u32 *id_in);
>   int iort_iommu_msi_get_resv_regions(struct device *dev, struct list_head *head);
> +unsigned int acpi_iort_get_zone_dma_size(void);
>   #else
>   static inline void acpi_iort_init(void) { }
>   static inline u32 iort_msi_map_id(struct device *dev, u32 id)
> @@ -55,6 +56,9 @@ static inline const struct iommu_ops *iort_iommu_configure_id(
>   static inline
>   int iort_iommu_msi_get_resv_regions(struct device *dev, struct list_head *head)
>   { return 0; }
> +
> +static inline unsigned int acpi_iort_get_zone_dma_size(void)
> +{ return 32; }
>   #endif
>   
>   #endif /* __ACPI_IORT_H__ */
> 

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Nicolas Saenz Julienne]

[-- Attachment #1: Type: text/plain, Size: 2194 bytes --]

On Thu, 2020-10-15 at 22:26 +0800, Hanjun Guo wrote:
> On 2020/10/15 3:12, Nicolas Saenz Julienne wrote:
> > From: Ard Biesheuvel <ardb@kernel.org>
> > 
> > We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
> > incorporating masters that can address less than 32 bits of DMA, in
> > particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
> > peripherals that can only address up to 1 GB (and its PCIe host
> > bridge can only access the bottom 3 GB)
> > 
> > Instructing the DMA layer about these limitations is straight-forward,
> > even though we had to fix some issues regarding memory limits set in
> > the IORT for named components, and regarding the handling of ACPI _DMA
> > methods. However, the DMA layer also needs to be able to allocate
> > memory that is guaranteed to meet those DMA constraints, for bounce
> > buffering as well as allocating the backing for consistent mappings.
> > 
> > This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
> > it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
> > problems with kdump, and potentially in other places where allocations
> > cannot cross zone boundaries. Therefore, we should avoid having two
> > separate DMA zones when possible.
> > 
> > So let's do an early scan of the IORT, and only create the ZONE_DMA
> > if we encounter any devices that need it. This puts the burden on
> > the firmware to describe such limitations in the IORT, which may be
> > redundant (and less precise) if _DMA methods are also being provided.
> > However, it should be noted that this situation is highly unusual for
> > arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
> > the _DMA method if implemented, and so we will not lose the ability to
> > perform streaming DMA outside the ZONE_DMA if the _DMA method permits
> > it.
> 
> Sorry, I'm still a little bit confused. With this patch, if we have
> a device which set the right _DMA method (DMA size >= 32), but with the
> wrong DMA size in IORT, we still have the ZONE_DMA created which
> is actually not needed?

Yes, that would be the case.

Regards,
Nicolas


[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Catalin Marinas]

On Thu, Oct 15, 2020 at 10:26:18PM +0800, Hanjun Guo wrote:
> On 2020/10/15 3:12, Nicolas Saenz Julienne wrote:
> > From: Ard Biesheuvel <ardb@kernel.org>
> > 
> > We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
> > incorporating masters that can address less than 32 bits of DMA, in
> > particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
> > peripherals that can only address up to 1 GB (and its PCIe host
> > bridge can only access the bottom 3 GB)
> > 
> > Instructing the DMA layer about these limitations is straight-forward,
> > even though we had to fix some issues regarding memory limits set in
> > the IORT for named components, and regarding the handling of ACPI _DMA
> > methods. However, the DMA layer also needs to be able to allocate
> > memory that is guaranteed to meet those DMA constraints, for bounce
> > buffering as well as allocating the backing for consistent mappings.
> > 
> > This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
> > it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
> > problems with kdump, and potentially in other places where allocations
> > cannot cross zone boundaries. Therefore, we should avoid having two
> > separate DMA zones when possible.
> > 
> > So let's do an early scan of the IORT, and only create the ZONE_DMA
> > if we encounter any devices that need it. This puts the burden on
> > the firmware to describe such limitations in the IORT, which may be
> > redundant (and less precise) if _DMA methods are also being provided.
> > However, it should be noted that this situation is highly unusual for
> > arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
> > the _DMA method if implemented, and so we will not lose the ability to
> > perform streaming DMA outside the ZONE_DMA if the _DMA method permits
> > it.
> 
> Sorry, I'm still a little bit confused. With this patch, if we have
> a device which set the right _DMA method (DMA size >= 32), but with the
> wrong DMA size in IORT, we still have the ZONE_DMA created which
> is actually not needed?

With the current kernel, we get a ZONE_DMA already with an arbitrary
size of 1GB that matches what RPi4 needs. We are trying to eliminate
such unnecessary ZONE_DMA based on some heuristics (well, something that
looks "better" than a OEM ID based quirk). Now, if we learn that IORT
for platforms in the field is that broken as to describe few bits-wide
DMA masks, we may have to go back to the OEM ID quirk.

-- 
Catalin

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Hanjun Guo]

On 2020/10/16 2:03, Catalin Marinas wrote:
> On Thu, Oct 15, 2020 at 10:26:18PM +0800, Hanjun Guo wrote:
>> On 2020/10/15 3:12, Nicolas Saenz Julienne wrote:
>>> From: Ard Biesheuvel <ardb@kernel.org>
>>>
>>> We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
>>> incorporating masters that can address less than 32 bits of DMA, in
>>> particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
>>> peripherals that can only address up to 1 GB (and its PCIe host
>>> bridge can only access the bottom 3 GB)
>>>
>>> Instructing the DMA layer about these limitations is straight-forward,
>>> even though we had to fix some issues regarding memory limits set in
>>> the IORT for named components, and regarding the handling of ACPI _DMA
>>> methods. However, the DMA layer also needs to be able to allocate
>>> memory that is guaranteed to meet those DMA constraints, for bounce
>>> buffering as well as allocating the backing for consistent mappings.
>>>
>>> This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
>>> it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
>>> problems with kdump, and potentially in other places where allocations
>>> cannot cross zone boundaries. Therefore, we should avoid having two
>>> separate DMA zones when possible.
>>>
>>> So let's do an early scan of the IORT, and only create the ZONE_DMA
>>> if we encounter any devices that need it. This puts the burden on
>>> the firmware to describe such limitations in the IORT, which may be
>>> redundant (and less precise) if _DMA methods are also being provided.
>>> However, it should be noted that this situation is highly unusual for
>>> arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
>>> the _DMA method if implemented, and so we will not lose the ability to
>>> perform streaming DMA outside the ZONE_DMA if the _DMA method permits
>>> it.
>>
>> Sorry, I'm still a little bit confused. With this patch, if we have
>> a device which set the right _DMA method (DMA size >= 32), but with the
>> wrong DMA size in IORT, we still have the ZONE_DMA created which
>> is actually not needed?
> 
> With the current kernel, we get a ZONE_DMA already with an arbitrary
> size of 1GB that matches what RPi4 needs. We are trying to eliminate
> such unnecessary ZONE_DMA based on some heuristics (well, something that
> looks "better" than a OEM ID based quirk). Now, if we learn that IORT
> for platforms in the field is that broken as to describe few bits-wide
> DMA masks, we may have to go back to the OEM ID quirk.

Some platforms using 0 as the memory size limit, for example D05 [0] and
D06 [1], I think we need to go back to the OEM ID quirk.

For D05/D06, there are multi interrupt controllers named as mbigen,
mbigen is using the named component to describe the mappings with
the ITS controller, and mbigen is using 0 as the memory size limit.

Also since the memory size limit for PCI RC was introduced by later
IORT revision, so firmware people may think it's fine to set that
as 0 because the system works without it.

Thanks
Hanjun

[0]:
https://github.com/tianocore/edk2-platforms/blob/master/Silicon/Hisilicon/Hi1616/D05AcpiTables/D05Iort.asl
[1]:
https://github.com/tianocore/edk2-platforms/blob/master/Silicon/Hisilicon/Hi1620/Hi1620AcpiTables/Hi1620Iort.asl

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Ard Biesheuvel]

On Fri, 16 Oct 2020 at 08:51, Hanjun Guo <guohanjun@huawei.com> wrote:
>
> On 2020/10/16 2:03, Catalin Marinas wrote:
> > On Thu, Oct 15, 2020 at 10:26:18PM +0800, Hanjun Guo wrote:
> >> On 2020/10/15 3:12, Nicolas Saenz Julienne wrote:
> >>> From: Ard Biesheuvel <ardb@kernel.org>
> >>>
> >>> We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
> >>> incorporating masters that can address less than 32 bits of DMA, in
> >>> particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
> >>> peripherals that can only address up to 1 GB (and its PCIe host
> >>> bridge can only access the bottom 3 GB)
> >>>
> >>> Instructing the DMA layer about these limitations is straight-forward,
> >>> even though we had to fix some issues regarding memory limits set in
> >>> the IORT for named components, and regarding the handling of ACPI _DMA
> >>> methods. However, the DMA layer also needs to be able to allocate
> >>> memory that is guaranteed to meet those DMA constraints, for bounce
> >>> buffering as well as allocating the backing for consistent mappings.
> >>>
> >>> This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
> >>> it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
> >>> problems with kdump, and potentially in other places where allocations
> >>> cannot cross zone boundaries. Therefore, we should avoid having two
> >>> separate DMA zones when possible.
> >>>
> >>> So let's do an early scan of the IORT, and only create the ZONE_DMA
> >>> if we encounter any devices that need it. This puts the burden on
> >>> the firmware to describe such limitations in the IORT, which may be
> >>> redundant (and less precise) if _DMA methods are also being provided.
> >>> However, it should be noted that this situation is highly unusual for
> >>> arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
> >>> the _DMA method if implemented, and so we will not lose the ability to
> >>> perform streaming DMA outside the ZONE_DMA if the _DMA method permits
> >>> it.
> >>
> >> Sorry, I'm still a little bit confused. With this patch, if we have
> >> a device which set the right _DMA method (DMA size >= 32), but with the
> >> wrong DMA size in IORT, we still have the ZONE_DMA created which
> >> is actually not needed?
> >
> > With the current kernel, we get a ZONE_DMA already with an arbitrary
> > size of 1GB that matches what RPi4 needs. We are trying to eliminate
> > such unnecessary ZONE_DMA based on some heuristics (well, something that
> > looks "better" than a OEM ID based quirk). Now, if we learn that IORT
> > for platforms in the field is that broken as to describe few bits-wide
> > DMA masks, we may have to go back to the OEM ID quirk.
>
> Some platforms using 0 as the memory size limit, for example D05 [0] and
> D06 [1], I think we need to go back to the OEM ID quirk.
>
> For D05/D06, there are multi interrupt controllers named as mbigen,
> mbigen is using the named component to describe the mappings with
> the ITS controller, and mbigen is using 0 as the memory size limit.
>
> Also since the memory size limit for PCI RC was introduced by later
> IORT revision, so firmware people may think it's fine to set that
> as 0 because the system works without it.
>

Hello Hanjun,

The patch only takes the address limit field into account if its value > 0.

Also, before commit 7fb89e1d44cb6aec ("ACPI/IORT: take _DMA methods
into account for named components"), the _DMA method was not taken
into account for named components at all, and only the IORT limit was
used, so I do not anticipate any problems with that.

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Ard Biesheuvel]

On Thu, 15 Oct 2020 at 12:31, Lorenzo Pieralisi
<lorenzo.pieralisi@arm.com> wrote:
>
> On Wed, Oct 14, 2020 at 09:12:09PM +0200, Nicolas Saenz Julienne wrote:
>
> [...]
>
> > +unsigned int __init acpi_iort_get_zone_dma_size(void)
> > +{
> > +     struct acpi_table_iort *iort;
> > +     struct acpi_iort_node *node, *end;
> > +     acpi_status status;
> > +     u8 limit = 32;
> > +     int i;
> > +
> > +     if (acpi_disabled)
> > +             return limit;
> > +
> > +     status = acpi_get_table(ACPI_SIG_IORT, 0,
> > +                             (struct acpi_table_header **)&iort);
> > +     if (ACPI_FAILURE(status))
> > +             return limit;
> > +
> > +     node = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->node_offset);
> > +     end = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->header.length);
> > +
> > +     for (i = 0; i < iort->node_count; i++) {
> > +             if (node >= end)
> > +                     break;
> > +
> > +             switch (node->type) {
> > +                     struct acpi_iort_named_component *ncomp;
> > +                     struct acpi_iort_root_complex *rc;
> > +
> > +             case ACPI_IORT_NODE_NAMED_COMPONENT:
> > +                     ncomp = (struct acpi_iort_named_component *)node->node_data;
> > +                     if (ncomp->memory_address_limit)
> > +                             limit = min(limit, ncomp->memory_address_limit);
> > +                     break;
> > +
> > +             case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
> > +                     rc = (struct acpi_iort_root_complex *)node->node_data;
> > +                     if (rc->memory_address_limit)
>
> You need to add a node revision check here, see rc_dma_get_range() in
> drivers/acpi/arm64/iort.c, otherwise we may be reading junk data
> in older IORT tables - acpica structures are always referring to the
> latest specs.
>

Indeed - apologies for not mentioning that when handing over the patch.

Also, we could use min_not_zero() here instead of the if ()

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Hanjun Guo]

Hi Ard,

On 2020/10/16 14:54, Ard Biesheuvel wrote:
> On Fri, 16 Oct 2020 at 08:51, Hanjun Guo <guohanjun@huawei.com> wrote:
>>
>> On 2020/10/16 2:03, Catalin Marinas wrote:
>>> On Thu, Oct 15, 2020 at 10:26:18PM +0800, Hanjun Guo wrote:
>>>> On 2020/10/15 3:12, Nicolas Saenz Julienne wrote:
>>>>> From: Ard Biesheuvel <ardb@kernel.org>
>>>>>
>>>>> We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
>>>>> incorporating masters that can address less than 32 bits of DMA, in
>>>>> particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
>>>>> peripherals that can only address up to 1 GB (and its PCIe host
>>>>> bridge can only access the bottom 3 GB)
>>>>>
>>>>> Instructing the DMA layer about these limitations is straight-forward,
>>>>> even though we had to fix some issues regarding memory limits set in
>>>>> the IORT for named components, and regarding the handling of ACPI _DMA
>>>>> methods. However, the DMA layer also needs to be able to allocate
>>>>> memory that is guaranteed to meet those DMA constraints, for bounce
>>>>> buffering as well as allocating the backing for consistent mappings.
>>>>>
>>>>> This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
>>>>> it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
>>>>> problems with kdump, and potentially in other places where allocations
>>>>> cannot cross zone boundaries. Therefore, we should avoid having two
>>>>> separate DMA zones when possible.
>>>>>
>>>>> So let's do an early scan of the IORT, and only create the ZONE_DMA
>>>>> if we encounter any devices that need it. This puts the burden on
>>>>> the firmware to describe such limitations in the IORT, which may be
>>>>> redundant (and less precise) if _DMA methods are also being provided.
>>>>> However, it should be noted that this situation is highly unusual for
>>>>> arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
>>>>> the _DMA method if implemented, and so we will not lose the ability to
>>>>> perform streaming DMA outside the ZONE_DMA if the _DMA method permits
>>>>> it.
>>>>
>>>> Sorry, I'm still a little bit confused. With this patch, if we have
>>>> a device which set the right _DMA method (DMA size >= 32), but with the
>>>> wrong DMA size in IORT, we still have the ZONE_DMA created which
>>>> is actually not needed?
>>>
>>> With the current kernel, we get a ZONE_DMA already with an arbitrary
>>> size of 1GB that matches what RPi4 needs. We are trying to eliminate
>>> such unnecessary ZONE_DMA based on some heuristics (well, something that
>>> looks "better" than a OEM ID based quirk). Now, if we learn that IORT
>>> for platforms in the field is that broken as to describe few bits-wide
>>> DMA masks, we may have to go back to the OEM ID quirk.
>>
>> Some platforms using 0 as the memory size limit, for example D05 [0] and
>> D06 [1], I think we need to go back to the OEM ID quirk.
>>
>> For D05/D06, there are multi interrupt controllers named as mbigen,
>> mbigen is using the named component to describe the mappings with
>> the ITS controller, and mbigen is using 0 as the memory size limit.
>>
>> Also since the memory size limit for PCI RC was introduced by later
>> IORT revision, so firmware people may think it's fine to set that
>> as 0 because the system works without it.
>>
> 
> Hello Hanjun,
> 
> The patch only takes the address limit field into account if its value > 0.

Sorry I missed the if (*->memory_address_limit) check, thanks
for the reminding.

> 
> Also, before commit 7fb89e1d44cb6aec ("ACPI/IORT: take _DMA methods
> into account for named components"), the _DMA method was not taken
> into account for named components at all, and only the IORT limit was
> used, so I do not anticipate any problems with that.

Then this patch is fine to me.

Thanks
Hanjun

Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan

[Hanjun Guo]

On 2020/10/16 15:27, Hanjun Guo wrote:
>> The patch only takes the address limit field into account if its value 
>> > 0.
> 
> Sorry I missed the if (*->memory_address_limit) check, thanks
> for the reminding.
> 
>>
>> Also, before commit 7fb89e1d44cb6aec ("ACPI/IORT: take _DMA methods
>> into account for named components"), the _DMA method was not taken
>> into account for named components at all, and only the IORT limit was
>> used, so I do not anticipate any problems with that.
> 
> Then this patch is fine to me.

Certainly we need to address Lorenzo's comments.

Thanks
Hanjun