Re: [PATCH v8 41/46] KVM: selftests: Provide function to look up guest_memfd details from gpa

[Fuad Tabba]

On Fri, 19 Jun 2026 at 01:32, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@xxxxxxxxxx> wrote:
>
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> Introduce a new helper, kvm_gpa_to_guest_memfd(), to find the
> guest_memfd-related details of a memory region that contains a given guest
> physical address (GPA).
>
> The function returns the file descriptor for the memfd, the offset into
> the file that corresponds to the GPA, and the number of bytes remaining
> in the region from that GPA.
>
> kvm_gpa_to_guest_memfd() was factored out from vm_guest_mem_fallocate();
> refactor vm_guest_mem_fallocate() to use the new helper.
>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>

Cheers,
/fuad

> ---
>  tools/testing/selftests/kvm/include/kvm_util.h |  3 +++
>  tools/testing/selftests/kvm/lib/kvm_util.c     | 37 ++++++++++++++++----------
>  2 files changed, 26 insertions(+), 14 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 79ab64ac8b869..3a6b1fa7f26ef 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -428,6 +428,9 @@ static inline void vm_enable_cap(struct kvm_vm *vm, u32 cap, u64 arg0)
>         vm_ioctl(vm, KVM_ENABLE_CAP, &enable_cap);
>  }
>
> +int kvm_gpa_to_guest_memfd(struct kvm_vm *vm, gpa_t gpa, off_t *fd_offset,
> +                          size_t *nr_bytes);
> +
>  /*
>   * KVM_SET_MEMORY_ATTRIBUTES{,2} overwrites _all_ attributes.  These
>   * flows need significant enhancements to support multiple attributes.
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 524ef97d634bf..0b2256ea65ff9 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -1305,27 +1305,20 @@ void vm_guest_mem_fallocate(struct kvm_vm *vm, u64 base, u64 size,
>                             bool punch_hole)
>  {
>         const int mode = FALLOC_FL_KEEP_SIZE | (punch_hole ? FALLOC_FL_PUNCH_HOLE : 0);
> -       struct userspace_mem_region *region;
>         u64 end = base + size;
> -       gpa_t gpa, len;
>         off_t fd_offset;
> -       int ret;
> +       int fd, ret;
> +       size_t len;
> +       gpa_t gpa;
>
>         for (gpa = base; gpa < end; gpa += len) {
> -               u64 offset;
> -
> -               region = userspace_mem_region_find(vm, gpa, gpa);
> -               TEST_ASSERT(region && region->region.flags & KVM_MEM_GUEST_MEMFD,
> -                           "Private memory region not found for GPA 0x%lx", gpa);
> +               fd = kvm_gpa_to_guest_memfd(vm, gpa, &fd_offset, &len);
> +               len = min(end - gpa, len);
>
> -               offset = gpa - region->region.guest_phys_addr;
> -               fd_offset = region->region.guest_memfd_offset + offset;
> -               len = min_t(u64, end - gpa, region->region.memory_size - offset);
> -
> -               ret = fallocate(region->region.guest_memfd, mode, fd_offset, len);
> +               ret = fallocate(fd, mode, fd_offset, len);
>                 TEST_ASSERT(!ret, "fallocate() failed to %s at %lx (len = %lu), fd = %d, mode = %x, offset = %lx",
>                             punch_hole ? "punch hole" : "allocate", gpa, len,
> -                           region->region.guest_memfd, mode, fd_offset);
> +                           fd, mode, fd_offset);
>         }
>  }
>
> @@ -1662,6 +1655,22 @@ void *addr_gpa2alias(struct kvm_vm *vm, gpa_t gpa)
>         return (void *) ((uintptr_t) region->host_alias + offset);
>  }
>
> +int kvm_gpa_to_guest_memfd(struct kvm_vm *vm, gpa_t gpa, off_t *fd_offset,
> +                          size_t *nr_bytes)
> +{
> +       struct userspace_mem_region *region;
> +       gpa_t gpa_offset;
> +
> +       region = userspace_mem_region_find(vm, gpa, gpa);
> +       TEST_ASSERT(region && region->region.flags & KVM_MEM_GUEST_MEMFD,
> +                   "guest_memfd memory region not found for GPA 0x%lx", gpa);
> +
> +       gpa_offset = gpa - region->region.guest_phys_addr;
> +       *fd_offset = region->region.guest_memfd_offset + gpa_offset;
> +       *nr_bytes = region->region.memory_size - gpa_offset;
> +       return region->region.guest_memfd;
> +}
> +
>  /* Create an interrupt controller chip for the specified VM. */
>  void vm_create_irqchip(struct kvm_vm *vm)
>  {
>
> --
> 2.55.0.rc0.738.g0c8ab3ebcc-goog
>
>