[PATCH v1 1/1] iommu/amd: Don't split flush for amd_iommu_domain_flush_all()

Weinan Liu
2026-04-14T21:06:38Z

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().

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>
---
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 760d5f4623b5..bcec8721d228 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1769,7 +1769,8 @@ 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 == CMD_INV_IOMMU_ALL_PAGES_ADDRESS) {
__domain_flush_pages(domain, address, size);

/* Wait until IOMMU TLB and all device IOTLB flushes are complete */
--
2.54.0.rc0.605.g598a273b03-goog