Re: [PATCH v1 1/6] backends/iommufd: Add a helper to invalidate user-managed HWPT

["Cédric Le Goater" <clg@redhat.com>]

Hello Zhenzhong,

On 5/28/25 08:04, Zhenzhong Duan wrote:
> This helper passes cache invalidation request from guest to invalidate
> stage-1 page table cache in host hardware.
> 
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> ---
>   include/system/iommufd.h |  4 ++++
>   backends/iommufd.c       | 33 +++++++++++++++++++++++++++++++++
>   backends/trace-events    |  1 +
>   3 files changed, 38 insertions(+)
> 
> diff --git a/include/system/iommufd.h b/include/system/iommufd.h
> index cbab75bfbf..5399519626 100644
> --- a/include/system/iommufd.h
> +++ b/include/system/iommufd.h
> @@ -61,6 +61,10 @@ bool iommufd_backend_get_dirty_bitmap(IOMMUFDBackend *be, uint32_t hwpt_id,
>                                         uint64_t iova, ram_addr_t size,
>                                         uint64_t page_size, uint64_t *data,
>                                         Error **errp);
> +bool iommufd_backend_invalidate_cache(IOMMUFDBackend *be, uint32_t id,
> +                                      uint32_t data_type, uint32_t entry_len,
> +                                      uint32_t *entry_num, void *data_ptr,
> +                                      Error **errp);
>   
>   #define TYPE_HOST_IOMMU_DEVICE_IOMMUFD TYPE_HOST_IOMMU_DEVICE "-iommufd"
>   #endif
> diff --git a/backends/iommufd.c b/backends/iommufd.c
> index b73f75cd0b..c8788a6438 100644
> --- a/backends/iommufd.c
> +++ b/backends/iommufd.c
> @@ -311,6 +311,39 @@ bool iommufd_backend_get_device_info(IOMMUFDBackend *be, uint32_t devid,
>       return true;
>   }
>   
> +bool iommufd_backend_invalidate_cache(IOMMUFDBackend *be, uint32_t id,
> +                                      uint32_t data_type, uint32_t entry_len,
> +                                      uint32_t *entry_num, void *data_ptr,
> +                                      Error **errp)
> +{
> +    int ret, fd = be->fd;
> +    uint32_t total_entries = *entry_num;
> +    struct iommu_hwpt_invalidate cache = {
> +        .size = sizeof(cache),
> +        .hwpt_id = id,
> +        .data_type = data_type,
> +        .entry_len = entry_len,
> +        .entry_num = total_entries,
> +        .data_uptr = (uintptr_t)data_ptr,

Minor, other helpers use a 'data' variable name.

> +    };
> +
> +    ret = ioctl(fd, IOMMU_HWPT_INVALIDATE, &cache);
> +    trace_iommufd_backend_invalidate_cache(fd, id, data_type, entry_len,
> +                                           total_entries, cache.entry_num,
> +                                           (uintptr_t)data_ptr,
> +                                           ret ? errno : 0);
> +    if (ret) {
> +        *entry_num = cache.entry_num;
> +        error_setg_errno(errp, errno, "IOMMU_HWPT_INVALIDATE failed:"
> +                         " totally %d entries, processed %d entries",
> +                         total_entries, cache.entry_num);
> +    } else {
> +        g_assert(total_entries == cache.entry_num);

Killing the VMM because a kernel device ioctl failed is brute force.
Can't we update the 'Error *' parameter instead to report that the
invalidation is partial or something went wrong ?

What kind of errors are we trying to catch ?

Looking at the kernel iommufd_hwpt_invalidate() routine and
intel_nested_cache_invalidate_user(), it doesn't seem possible to
return a different number of cache entries. Are you anticipating
other implementations (sMMU) ?

Thanks,

C.