[PATCH v9 11/13] xen/arm: introduce GNTTABOP_cache_flush

Stefano Stabellini
2014-11-12T11:48:05Z

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>

---

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 | 34 ++++++++++++++++++++++++++++++++--
include/xen/interface/grant_table.h | 19 +++++++++++++++++++
2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index 28ebf3e..351b24a 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);
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