xen/arm: introduce GNTTABOP_cache_flush

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@eu.citrix.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

1 files changed, 32 insertions, 2 deletions

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index 28ebf3ecee4e..351b24a979d4 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -12,6 +12,7 @@
 #include <linux/swiotlb.h>
 
 #include <xen/xen.h>
+#include <xen/interface/grant_table.h>
 #include <xen/interface/memory.h>
 #include <xen/swiotlb-xen.h>
 
@@ -24,12 +25,14 @@ enum dma_cache_op {
        DMA_UNMAP,
        DMA_MAP,
 };
+static bool hypercall_cflush = false;
 
 /* functions called by SWIOTLB */
 
 static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
         size_t size, enum dma_data_direction dir, enum dma_cache_op op)
 {
+        struct gnttab_cache_flush cflush;
         unsigned long pfn;
         size_t left = size;
 
@@ -39,7 +42,26 @@ static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
         do {
                 size_t len = left;
         
-                /* TODO: cache flush */
+                /* buffers in highmem or foreign pages cannot cross page
+                 * boundaries */
+                if (len + offset > PAGE_SIZE)
+                        len = PAGE_SIZE - offset;
+
+                cflush.op = 0;
+                cflush.a.dev_bus_addr = pfn << PAGE_SHIFT;
+                cflush.offset = offset;
+                cflush.length = len;
+
+                if (op == DMA_UNMAP && dir != DMA_TO_DEVICE)
+                        cflush.op = GNTTAB_CACHE_INVAL;
+                if (op == DMA_MAP) {
+                        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);
 
                 offset = 0;
                 pfn++;
@@ -104,7 +126,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
                            unsigned long pfn,
                            unsigned long mfn)
 {
-        return ((pfn != mfn) && !is_device_dma_coherent(dev));
+        return (!hypercall_cflush && (pfn != mfn) && !is_device_dma_coherent(dev));
 }
 
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
@@ -147,10 +169,18 @@ 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);