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

["Suthikulpanit, Suravee" <suravee.suthikulpanit@amd.com>]

On 4/15/2026 6:55 AM, Samiullah Khawaja wrote:
> On Tue, Apr 14, 2026 at 09:06:26PM +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(-)
>>
>> 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
>>
>>
> 
> Reviewed-by: Samiullah Khawaja <skhawaja@google.com>

Thanks,

Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>