[PATCH v3 0/2] introduce GNTTABOP_cache_flush

[PATCH v3 0/2] introduce GNTTABOP_cache_flush

[Stefano Stabellini]

Hi all,
this patch series introduces support for GNTTABOP_cache_flush to perform
cache maintenance operation on foreign pages and reverts the current
code based on XENFEAT_grant_map_identity.


Changes in v3:
- fix the cache maintenance op call to match what Linux does natively;
- update the hypercall interface to match Xen.

Changes in v2:
- remove the definition of XENFEAT_grant_map_identity;
- update the hypercall interface to match Xen;
- call the interface on a single page at a time.


Stefano Stabellini (2):
      xen/arm: remove handling of XENFEAT_grant_map_identity
      xen/arm: introduce GNTTABOP_cache_flush

 arch/arm/xen/enlighten.c            |    5 --
 arch/arm/xen/mm32.c                 |  108 +++++++----------------------------
 include/xen/interface/features.h    |    3 -
 include/xen/interface/grant_table.h |   19 ++++++
 4 files changed, 41 insertions(+), 94 deletions(-)

[PATCH v3 1/2] xen/arm: remove handling of XENFEAT_grant_map_identity

[Stefano Stabellini]

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

---
Changes in v2:

- remove the definition of XENFEAT_grant_map_identity.
---
 arch/arm/xen/enlighten.c         |    5 ---
 arch/arm/xen/mm32.c              |   85 +-------------------------------------
 include/xen/interface/features.h |    3 --
 3 files changed, 1 insertion(+), 92 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 0e15f01..c7ca936 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -261,11 +261,6 @@ static int __init xen_guest_init(void)
 
 	xen_setup_features();
 
-	if (!xen_feature(XENFEAT_grant_map_identity)) {
-		pr_warn("Please upgrade your Xen.\n"
-				"If your platform has any non-coherent DMA devices, they won't work properly.\n");
-	}
-
 	if (xen_feature(XENFEAT_dom0))
 		xen_start_info->flags |= SIF_INITDOMAIN|SIF_PRIVILEGED;
 	else
diff --git a/arch/arm/xen/mm32.c b/arch/arm/xen/mm32.c
index 3b99860..a5a93fc 100644
--- a/arch/arm/xen/mm32.c
+++ b/arch/arm/xen/mm32.c
@@ -5,70 +5,6 @@
 
 #include <xen/features.h>
 
-static DEFINE_PER_CPU(unsigned long, xen_mm32_scratch_virt);
-static DEFINE_PER_CPU(pte_t *, xen_mm32_scratch_ptep);
-
-static int alloc_xen_mm32_scratch_page(int cpu)
-{
-	struct page *page;
-	unsigned long virt;
-	pmd_t *pmdp;
-	pte_t *ptep;
-
-	if (per_cpu(xen_mm32_scratch_ptep, cpu) != NULL)
-		return 0;
-
-	page = alloc_page(GFP_KERNEL);
-	if (page == NULL) {
-		pr_warn("Failed to allocate xen_mm32_scratch_page for cpu %d\n", cpu);
-		return -ENOMEM;
-	}
-
-	virt = (unsigned long)__va(page_to_phys(page));
-	pmdp = pmd_offset(pud_offset(pgd_offset_k(virt), virt), virt);
-	ptep = pte_offset_kernel(pmdp, virt);
-
-	per_cpu(xen_mm32_scratch_virt, cpu) = virt;
-	per_cpu(xen_mm32_scratch_ptep, cpu) = ptep;
-
-	return 0;
-}
-
-static int xen_mm32_cpu_notify(struct notifier_block *self,
-				    unsigned long action, void *hcpu)
-{
-	int cpu = (long)hcpu;
-	switch (action) {
-	case CPU_UP_PREPARE:
-		if (alloc_xen_mm32_scratch_page(cpu))
-			return NOTIFY_BAD;
-		break;
-	default:
-		break;
-	}
-	return NOTIFY_OK;
-}
-
-static struct notifier_block xen_mm32_cpu_notifier = {
-	.notifier_call	= xen_mm32_cpu_notify,
-};
-
-static void* xen_mm32_remap_page(dma_addr_t handle)
-{
-	unsigned long virt = get_cpu_var(xen_mm32_scratch_virt);
-	pte_t *ptep = __get_cpu_var(xen_mm32_scratch_ptep);
-
-	*ptep = pfn_pte(handle >> PAGE_SHIFT, PAGE_KERNEL);
-	local_flush_tlb_kernel_page(virt);
-
-	return (void*)virt;
-}
-
-static void xen_mm32_unmap(void *vaddr)
-{
-	put_cpu_var(xen_mm32_scratch_virt);
-}
-
 
 /* functions called by SWIOTLB */
 
@@ -88,13 +24,7 @@ static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
 	
 		if (!pfn_valid(pfn))
 		{
-			/* Cannot map the page, we don't know its physical address.
-			 * Return and hope for the best */
-			if (!xen_feature(XENFEAT_grant_map_identity))
-				return;
-			vaddr = xen_mm32_remap_page(handle) + offset;
-			op(vaddr, len, dir);
-			xen_mm32_unmap(vaddr - offset);
+			/* TODO: cache flush */
 		} else {
 			struct page *page = pfn_to_page(pfn);
 
@@ -181,22 +111,9 @@ void xen_dma_sync_single_for_device(struct device *hwdev,
 
 int __init xen_mm32_init(void)
 {
-	int cpu;
-
 	if (!xen_initial_domain())
 		return 0;
 
-	register_cpu_notifier(&xen_mm32_cpu_notifier);
-	get_online_cpus();
-	for_each_online_cpu(cpu) {
-		if (alloc_xen_mm32_scratch_page(cpu)) {
-			put_online_cpus();
-			unregister_cpu_notifier(&xen_mm32_cpu_notifier);
-			return -ENOMEM;
-		}
-	}
-	put_online_cpus();
-
 	return 0;
 }
 arch_initcall(xen_mm32_init);
diff --git a/include/xen/interface/features.h b/include/xen/interface/features.h
index 14334d0..131a6cc 100644
--- a/include/xen/interface/features.h
+++ b/include/xen/interface/features.h
@@ -53,9 +53,6 @@
 /* operation as Dom0 is supported */
 #define XENFEAT_dom0                      11
 
-/* Xen also maps grant references at pfn = mfn */
-#define XENFEAT_grant_map_identity        12
-
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */
-- 
1.7.10.4

[PATCH v3 2/2] xen/arm: introduce GNTTABOP_cache_flush

[Stefano Stabellini]

Introduce support for new hypercall GNTTABOP_cache_flush.
Use it to perform cache flashing on pages used for dma when necessary.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

---
Changes in v3:
- fix the cache maintenance op call to match what Linux does natively;
- update the hypercall interface to match Xen.

Changes in v2:
- update the hypercall interface to match Xen;
- call the interface on a single page at a time.
---
 arch/arm/xen/mm32.c                 |   27 +++++++++++++++++++++++----
 include/xen/interface/grant_table.h |   19 +++++++++++++++++++
 2 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/arch/arm/xen/mm32.c b/arch/arm/xen/mm32.c
index a5a93fc..ec2eb02 100644
--- a/arch/arm/xen/mm32.c
+++ b/arch/arm/xen/mm32.c
@@ -4,6 +4,9 @@
 #include <linux/highmem.h>
 
 #include <xen/features.h>
+#include <xen/interface/grant_table.h>
+
+#include <asm/xen/hypercall.h>
 
 
 /* functions called by SWIOTLB */
@@ -22,16 +25,32 @@ static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
 		size_t len = left;
 		void *vaddr;
 	
+		if (len + offset > PAGE_SIZE)
+			len = PAGE_SIZE - offset;
+
 		if (!pfn_valid(pfn))
 		{
-			/* TODO: cache flush */
+			struct gnttab_cache_flush cflush;
+
+			cflush.op = 0;
+			cflush.a.dev_bus_addr = pfn << PAGE_SHIFT;
+			cflush.offset = offset;
+			cflush.length = len;
+
+			if (op == dmac_unmap_area && dir != DMA_TO_DEVICE)
+				cflush.op = GNTTAB_CACHE_INVAL;
+			if (op == dmac_map_area) {
+				if (dir == DMA_FROM_DEVICE)
+					cflush.op = GNTTAB_CACHE_INVAL;
+				else
+					cflush.op = GNTTAB_CACHE_CLEAN;
+			}
+			if (cflush.op)
+				HYPERVISOR_grant_table_op(GNTTABOP_cache_flush, &cflush, 1);
 		} else {
 			struct page *page = pfn_to_page(pfn);
 
 			if (PageHighMem(page)) {
-				if (len + offset > PAGE_SIZE)
-					len = PAGE_SIZE - offset;
-
 				if (cache_is_vipt_nonaliasing()) {
 					vaddr = kmap_atomic(page);
 					op(vaddr + offset, len, dir);
diff --git a/include/xen/interface/grant_table.h b/include/xen/interface/grant_table.h
index e40fae9..bcce564 100644
--- a/include/xen/interface/grant_table.h
+++ b/include/xen/interface/grant_table.h
@@ -479,6 +479,25 @@ struct gnttab_get_version {
 DEFINE_GUEST_HANDLE_STRUCT(gnttab_get_version);
 
 /*
+ * Issue one or more cache maintenance operations on a portion of a
+ * page granted to the calling domain by a foreign domain.
+ */
+#define GNTTABOP_cache_flush          12
+struct gnttab_cache_flush {
+    union {
+        uint64_t dev_bus_addr;
+        grant_ref_t ref;
+    } a;
+    uint16_t offset;   /* offset from start of grant */
+    uint16_t length;   /* size within the grant */
+#define GNTTAB_CACHE_CLEAN          (1<<0)
+#define GNTTAB_CACHE_INVAL          (1<<1)
+#define GNTTAB_CACHE_SOURCE_GREF    (1<<31)
+    uint32_t op;
+};
+DEFINE_GUEST_HANDLE_STRUCT(gnttab_cache_flush);
+
+/*
  * Bitfield values for update_pin_status.flags.
  */
  /* Map the grant entry for access by I/O devices. */
-- 
1.7.10.4

Re: [Xen-devel] [PATCH v3 1/2] xen/arm: remove handling of XENFEAT_grant_map_identity

[David Vrabel]

On 08/10/14 14:04, Stefano Stabellini wrote:
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

Reviewed-by: David Vrabel <david.vrabel@citrix.com>

But you should include in commit description the reason why this is
being removed.

David

Re: [Xen-devel] [PATCH v3 2/2] xen/arm: introduce GNTTABOP_cache_flush

[David Vrabel]

On 08/10/14 14:04, Stefano Stabellini wrote:
> Introduce support for new hypercall GNTTABOP_cache_flush.
> Use it to perform cache flashing on pages used for dma when necessary.

This still think all these additional hypercalls in the hot path are
going to limit performance but on the understanding that this is only
used for non-coherent devices and a lack of anything better:

Reviewed-by: David Vrabel <david.vrabel@citrix.com>

With one comment below.

> --- a/arch/arm/xen/mm32.c
> +++ b/arch/arm/xen/mm32.c
> @@ -4,6 +4,9 @@
>  #include <linux/highmem.h>
>  
>  #include <xen/features.h>
> +#include <xen/interface/grant_table.h>
> +
> +#include <asm/xen/hypercall.h>
>  
>  
>  /* functions called by SWIOTLB */
> @@ -22,16 +25,32 @@ static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
>  		size_t len = left;
>  		void *vaddr;
>  	
> +		if (len + offset > PAGE_SIZE)
> +			len = PAGE_SIZE - offset;

Since this looks like it would result in failing the clean/invalidate
the trailing part of the buffer, I think this needs a comment explaining
why this is safe.  i.e., buffers in highmem or foreign pages cannot
cross page boundaries.

David