Re: [PATCH v0 14/15] mshv: Remove mapping of mmio space during map user ioctl

Stanislav Kinsburskii
2026-01-21T01:41:52Z

On Mon, Jan 19, 2026 at 10:42:29PM -0800, Mukesh R wrote:
> From: Mukesh Rathor <mrathor@linux.microsoft.com>
>
> VFIO no longer puts the mmio pfn in vma->vm_pgoff. So, remove code
> that is using it to map mmio space. It is broken and will cause
> panic.
>
> Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
> ---
> drivers/hv/mshv_root_main.c | 20 ++++----------------
> 1 file changed, 4 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index 27313419828d..03f3aa9f5541 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -1258,16 +1258,8 @@ static int mshv_prepare_pinned_region(struct mshv_mem_region *region)
> }
>
> /*
> - * This maps two things: guest RAM and for pci passthru mmio space.
> - *
> - * mmio:
> - * - vfio overloads vm_pgoff to store the mmio start pfn/spa.
> - * - Two things need to happen for mapping mmio range:
> - * 1. mapped in the uaddr so VMM can access it.
> - * 2. mapped in the hwpt (gfn <-> mmio phys addr) so guest can access it.
> - *
> - * This function takes care of the second. The first one is managed by vfio,
> - * and hence is taken care of via vfio_pci_mmap_fault().
> + * This is called for both user ram and mmio space. The mmio space is not
> + * mapped here, but later during intercept.
> */
> static long
> mshv_map_user_memory(struct mshv_partition *partition,
> @@ -1276,7 +1268,6 @@ mshv_map_user_memory(struct mshv_partition *partition,
> struct mshv_mem_region *region;
> struct vm_area_struct *vma;
> bool is_mmio;
> - ulong mmio_pfn;
> long ret;
>
> if (mem.flags & BIT(MSHV_SET_MEM_BIT_UNMAP) ||
> @@ -1286,7 +1277,6 @@ mshv_map_user_memory(struct mshv_partition *partition,
> mmap_read_lock(current->mm);
> vma = vma_lookup(current->mm, mem.userspace_addr);
> is_mmio = vma ? !!(vma->vm_flags & (VM_IO | VM_PFNMAP)) : 0;
> - mmio_pfn = is_mmio ? vma->vm_pgoff : 0;
> mmap_read_unlock(current->mm);
>
> if (!vma)
> @@ -1313,10 +1303,8 @@ mshv_map_user_memory(struct mshv_partition *partition,
> HV_MAP_GPA_NO_ACCESS, NULL);
> break;
> case MSHV_REGION_TYPE_MMIO:
> - ret = hv_call_map_mmio_pages(partition->pt_id,
> - region->start_gfn,
> - mmio_pfn,
> - region->nr_pages);
> + /* mmio mappings are handled later during intercepts */
> + ret = 0;

No need updating ret here: it's 0 after the previous call.

Thanks,
Stanislav

> break;
> }
>
> --
> 2.51.2.vfs.0.1
>