Re: [PATCH v3 1/2] hw/i386/amd_iommu: Fix device setup failure when PT is on.

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 16/5/25 12:05, Sairaj Kodilkar wrote:
> Commit c1f46999ef506 ("amd_iommu: Add support for pass though mode")
> introduces the support for "pt" flag by enabling nodma memory when
> "pt=off". This allowed VFIO devices to successfully register notifiers
> by using nodma region.
> 
> But, This also broke things when guest is booted with the iommu=nopt
> because, devices bypass the IOMMU and use untranslated addresses (IOVA) to
> perform DMA reads/writes to the nodma memory region, ultimately resulting in
> a failure to setup the devices in the guest.
> 
> Fix the above issue by always enabling the amdvi_dev_as->iommu memory region.
> But this will once again cause VFIO devices to fail while registering the
> notifiers with AMD IOMMU memory region.
> 
> Fixes: c1f46999ef506 ("amd_iommu: Add support for pass though mode")
> Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>
> Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
> ---
>   hw/i386/amd_iommu.c | 12 ++----------
>   1 file changed, 2 insertions(+), 10 deletions(-)
> 
> diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> index 5f9b95279997..df8ba5d39ada 100644
> --- a/hw/i386/amd_iommu.c
> +++ b/hw/i386/amd_iommu.c
> @@ -1426,7 +1426,6 @@ static AddressSpace *amdvi_host_dma_iommu(PCIBus *bus, void *opaque, int devfn)
>       AMDVIState *s = opaque;
>       AMDVIAddressSpace **iommu_as, *amdvi_dev_as;
>       int bus_num = pci_bus_num(bus);
> -    X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(s);
>   
>       iommu_as = s->address_spaces[bus_num];
>   
> @@ -1486,15 +1485,8 @@ static AddressSpace *amdvi_host_dma_iommu(PCIBus *bus, void *opaque, int devfn)
>                                               AMDVI_INT_ADDR_FIRST,
>                                               &amdvi_dev_as->iommu_ir, 1);
>   
> -        if (!x86_iommu->pt_supported) {
> -            memory_region_set_enabled(&amdvi_dev_as->iommu_nodma, false);
> -            memory_region_set_enabled(MEMORY_REGION(&amdvi_dev_as->iommu),
> -                                      true);
> -        } else {
> -            memory_region_set_enabled(MEMORY_REGION(&amdvi_dev_as->iommu),
> -                                      false);
> -            memory_region_set_enabled(&amdvi_dev_as->iommu_nodma, true);
> -        }
> +        memory_region_set_enabled(&amdvi_dev_as->iommu_nodma, false);

I have no clue about this device but wonder what is the usefulness of
iommu_nodma now, isn't it dead code?

> +        memory_region_set_enabled(MEMORY_REGION(&amdvi_dev_as->iommu), true);
>       }
>       return &iommu_as[devfn]->as;
>   }