Re: [PATCH v3 00/22] AMD vIOMMU: DMA remapping support for VFIO devices

["Cédric Le Goater" <clg@redhat.com>]

Hello Alejandro,

On 9/19/25 23:34, Alejandro Jimenez wrote:
> This series adds support for guests using the AMD vIOMMU to enable DMA remapping
> for VFIO devices. Please see v1[0] cover letter for additional details such as
> example QEMU command line parameters used in testing.
> 
> I have sanity tested on an AMD EPYC Genoa host, booting a Linux guest with
> 'iommu.passthrough=0' and several CX6 VFs, and there are no issues during
> typical guest operation.
> 
> When using the non-default parameter 'iommu.forcedac=1' in the guest kernel
> cmdline, this initially fails due to a VFIO integer overflow bug which requires
> the following fix in the host kernel:
> 
> https://github.com/aljimenezb/linux/commit/014be8cafe7464d278729583a2dd5d94514e2e2a
> This is a work in progress as there are other locations in the driver that are
> susceptible to overflows, but the above is sufficient to fix the initial
> problem.
> 
> Even after that fix is applied, I see an issue on guest reboot when 'forcedac=1'
> is in use. Although the guest boots, the VF is not properly initialized, failing
> with a timeout. Once the guest reaches userspace the VF driver can be reloaded
> and it then works as expected. I am still investigating the root cause for this
> issue, and will need to discuss all the steps I have tried to eliminate
> potential sources of errors in a separate thread.
> 
> I am sending v3 despite this known issue since forcedac=1 is not a default or
> commonly known/used setting. Having the large portions of the infrastructure for
> DMA remapping already in place (and working) will make it easier to debug this
> corner case and get feedback/testing from the community. I hope this is a viable
> approach, otherwise I am happy to discuss all the steps I have taken to debug
> this issue in this thread and test any suggestions to address it.
> 
> Changes since v2[2]:
> - P5: Fixed missed check for AMDVI_FR_DTE_RTR_ERR in amdvi_do_translate() (Sairaj)
> - P6: Reword commit message to clarify the need to discern between empty PTEs and errors (Vasant)
> - P9: Use correct enum type for notifier flags and remove whitespace changes (Sairaj)
> - P11: Fixed integer overflow bug when guest uses iommu.forcedac=1. Fixed in P8. (Sairaj)
> - P15: Fixed typo in commit message (Sairaj)
> - P16: On reset, use passthrough mode by default on all address spaces (Sairaj)
> - P18: Enforce isolation by using DMA mode on errors retrieving DTE (Ethan & Sairaj)
> - P20: Removed unused pte_override_page_mask() and pte_get_page_mask() to avoid -Wunused-function error.
> - Add HATDis support patches from Joao Martins (HATDis available in Linux since [1])
> 
> Thank you,
> Alejandro
> 
> [0] https://lore.kernel.org/all/20250414020253.443831-1-alejandro.j.jimenez@oracle.com/
> [1] https://lore.kernel.org/all/cover.1749016436.git.Ankit.Soni@amd.com/
> [2] https://lore.kernel.org/qemu-devel/20250502021605.1795985-1-alejandro.j.jimenez@oracle.com/
> 
> Alejandro Jimenez (20):
>    memory: Adjust event ranges to fit within notifier boundaries
>    amd_iommu: Document '-device amd-iommu' common options
>    amd_iommu: Reorder device and page table helpers
>    amd_iommu: Helper to decode size of page invalidation command
>    amd_iommu: Add helper function to extract the DTE
>    amd_iommu: Return an error when unable to read PTE from guest memory
>    amd_iommu: Add helpers to walk AMD v1 Page Table format
>    amd_iommu: Add a page walker to sync shadow page tables on
>      invalidation
>    amd_iommu: Add basic structure to support IOMMU notifier updates
>    amd_iommu: Sync shadow page tables on page invalidation
>    amd_iommu: Use iova_tree records to determine large page size on UNMAP
>    amd_iommu: Unmap all address spaces under the AMD IOMMU on reset
>    amd_iommu: Add replay callback
>    amd_iommu: Invalidate address translations on INVALIDATE_IOMMU_ALL
>    amd_iommu: Toggle memory regions based on address translation mode
>    amd_iommu: Set all address spaces to use passthrough mode on reset
>    amd_iommu: Add dma-remap property to AMD vIOMMU device
>    amd_iommu: Toggle address translation mode on devtab entry
>      invalidation
>    amd_iommu: Do not assume passthrough translation when DTE[TV]=0
>    amd_iommu: Refactor amdvi_page_walk() to use common code for page walk
> 
> Joao Martins (2):
>    i386/intel-iommu: Move dma_translation to x86-iommu
>    amd_iommu: HATDis/HATS=11 support
> 
>   hw/i386/acpi-build.c        |    6 +-
>   hw/i386/amd_iommu.c         | 1056 ++++++++++++++++++++++++++++++-----
>   hw/i386/amd_iommu.h         |   51 ++


The current status of AMD-Vi Emulation in MAINTAINERS is Orphan.
Since this series is about to be merged, should AMD-Vi be considered
maintained now ? and if so by whom ?

Thanks,

C.




>   hw/i386/intel_iommu.c       |    5 +-
>   hw/i386/x86-iommu.c         |    1 +
>   include/hw/i386/x86-iommu.h |    1 +
>   qemu-options.hx             |   23 +
>   system/memory.c             |   10 +-
>   8 files changed, 999 insertions(+), 154 deletions(-)> 
> 
> base-commit: ab8008b231e758e03c87c1c483c03afdd9c02e19