[Xen-devel] [PATCH v5 6/6] xen/arm: introduce GNTTABOP_cache_flush

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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

If GNTTABOP_cache_flush is supported by the hypervisor, we don't need to
bounce dma map operations that involve foreign grants and non-coherent
devices.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

---

Changes in v5:
- rename hypercall_flush to hypercall_cflush;
- remove spurious change.

Changes in v4:
- add comment;
- avoid bouncing dma map operations that involve foreign grants and
non-coherent devices if GNTTABOP_cache_flush is provided by Xen.

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/mm.c                   |   39 ++++++++++++++++++++++++++++++-----
 include/xen/interface/grant_table.h |   19 +++++++++++++++++
 2 files changed, 53 insertions(+), 5 deletions(-)

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index 728c245..26ad47c 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -11,6 +11,7 @@
 #include <linux/swiotlb.h>
 
 #include <xen/xen.h>
+#include <xen/interface/grant_table.h>
 #include <xen/interface/memory.h>
 #include <xen/swiotlb-xen.h>
 
@@ -45,6 +46,8 @@ static inline void *kmap_high_get(struct page *page)
 static inline void kunmap_high(struct page *page) {}
 #endif
 
+static bool hypercall_cflush = false;
+
 
 /* functions called by SWIOTLB */
 
@@ -61,17 +64,35 @@ static void dma_cache_maint(dma_addr_t handle, unsigned 
long offset,
        do {
                size_t len = left;
                void *vaddr;
+
+               /* buffers in highmem or foreign pages cannot cross page
+                * boundaries */
+               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);
@@ -144,7 +165,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
                                                   unsigned long pfn,
                                                   unsigned long mfn)
 {
-       return ((pfn != mfn) && !xen_is_dma_coherent(dev));
+       return (!hypercall_cflush && (pfn != mfn) && !xen_is_dma_coherent(dev));
 }
 
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
@@ -187,10 +208,18 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
 
 int __init xen_mm_init(void)
 {
+       struct gnttab_cache_flush cflush;
        if (!xen_initial_domain())
                return 0;
        xen_swiotlb_init(1, false);
        xen_dma_ops = &xen_swiotlb_dma_ops;
+
+       cflush.op = 0;
+       cflush.a.dev_bus_addr = 0;
+       cflush.offset = 0;
+       cflush.length = 0;
+       if (HYPERVISOR_grant_table_op(GNTTABOP_cache_flush, &cflush, 1) != 
-ENOSYS)
+               hypercall_cflush = true;
        return 0;
 }
 arch_initcall(xen_mm_init);
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


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