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

Commit Message

Stefano Stabellini Oct. 8, 2014, 1:04 p.m. UTC

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 <[e-mail]>

---
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(-)

Comments

David Vrabel Oct. 9, 2014, 11 a.m. UTC | #1

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 <[e-mail]>

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

Patch

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. */