[PATCH v2 1/1] iommu/amd: Don't split flush for amd_iommu_domain_flush_all()

[Weinan Liu <wnliu@google.com>]

We have observed multiple full invalidations occurring during device
detach when we are done using the vfio-device.

blocked_domain_attach_device()
  -> detach_device()
    -> amd_iommu_domain_flush_all()
      -> amd_iommu_domain_flush_pages(..., CMD_INV_IOMMU_ALL_PAGES_ADDRESS)

      	while (size != 0) {

          -> __domain_flush_pages( flush_size /* power of 2 flush_size */)
            -> domain_flush_pages_v1()
              -> build_inv_iommu_pages()
                -> build_inv_address()

         }

build_inv_address() will trigger a full invalidation  if the chunk
size > (1 << 51). Consequently, the guest will issue multiple full
invalidations for a single call to  amd_iommu_domain_flush_all()

Without this patch, we will see 10 time instead of 1 time full
invalidations for every amd_iommu_domain_flush_all().

Cc: stable@vger.kernel.org
Fixes: a270be1b3fdf ("iommu/amd: Use only natural aligned flushes in a VM")
Suggested-by: Josef Bacik <josef@toxicpanda.com>
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Weinan Liu <wnliu@google.com>
Reviewed-by: Wei Wang <wei.w.wang@hotmail.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
 drivers/iommu/amd/iommu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 57dc8fabc7d9..15ffc4742183 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1774,7 +1774,8 @@ void amd_iommu_domain_flush_pages(struct protection_domain *domain,
 {
 	lockdep_assert_held(&domain->lock);
 
-	if (likely(!amd_iommu_np_cache)) {
+	if (likely(!amd_iommu_np_cache) ||
+		size >= (1ULL<<52)) {
 		__domain_flush_pages(domain, address, size);
 
 		/* Wait until IOMMU TLB and all device IOTLB flushes are complete */
-- 
2.54.0.823.g6e5bcc1fc9-goog