On Mon, May 12, 2025 at 09:35:37AM +0530, Sairaj Kodilkar wrote:
> Current amd_iommu enables the iommu_nodma address space when pt_supported
Currently,
> flag is on. This causes device to bypass the IOMMU and use untranslated
devices
> address to perform DMA when guest kernel uses DMA mode, resulting in
the guest
> failure to setup the devices in the guest.
a failure
>
> Fix the issue by always enabling amdvi_dev_as->iommu, which is explicitly
> created as an IOMMU memory region (i.e. a memory region with mr->is_iommu
> == true), and it is meant to support DMA remapping. It is relying on the
> "side effect" that VFIO will try to register notifiers for memory regions
> that are an "IOMMU" (i.e. pass the check in memory_region_is_iommu()),
> and later fail when trying to register the notifier.
what will fail? what is meant for what? confused.
>
> Fixes: c1f46999ef506 ("amd_iommu: Add support for pass though mode")
explain the connection with this commit pls. did it work
prior to that?
> Signed-off-by: Sairaj Kodilkar <sarun...@amd.com>
> Reviewed-by: Vasant Hegde <vasant.he...@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);
> + memory_region_set_enabled(MEMORY_REGION(&amdvi_dev_as->iommu), true);
> }
> return &iommu_as[devfn]->as;
> }
> --
> 2.34.1
