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

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Apr 15, 2026 at 12:30:46AM +0000, Weinan Liu wrote:
> 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(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason