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

[Mukesh R]

On 1/23/26 10:34, Nuno Das Neves wrote:

On 1/19/2026 10:42 PM, Mukesh R wrote:

From: Mukesh Rathor <mrat...@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.

What is the reason for having this as a separate commit from patch 15?
It seems like removing this code and adding the mmio intercept
handling could be done in one patch.

Just ease of review and porting patches from this branch to that
branch to that release to this release... I am sure someone would
have asked for this to be a separate patch :).

Thanks,
-Mukesh

Signed-off-by: Mukesh Rathor <mrat...@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;
                break;
        }