Re: [PATCH v4 1/3] virtio-gpu: validate host page alignment for MAP_FIXED blobs

[Lucas Amaral <lucaaamaral@gmail.com>]

Hi Alex,

Thanks for looking at this.

> What was your test case? Is it possible to publish some images for a
> functional test?

The test case is running a Linux VM with virtio-gpu Venus (Vulkan
passthrough) on an Apple Silicon Mac:

  - Host: macOS ARM64 with 16KB pages
  - Guest: Linux ARM64 with 4KB pages
  - GPU: virtio-gpu-gl with Venus/virglrenderer + MoltenVK

When the guest allocates a blob resource with a 4KB-aligned size,
mmap(MAP_FIXED) fails with EINVAL because the size isn't aligned to
the host's 16KB page boundary. Without this patch the blob resource
is silently unusable — the guest sees no GPU output.

Reproducing it requires the full macOS Venus stack, which includes
patches across multiple projects:

  QEMU (this series + two others on the list):
  - Stack A: ISV=0 data abort emulation (v6, R-b by Mohamed)
    https://patchew.org/QEMU/20260409220614.65558-1-lucaaamaral@gmail.com/
  - Stack B: this series (hvf map granule + MAP_FIXED alignment)
  - Stack C: Venus without OpenGL (v5)
    https://patchew.org/QEMU/20260317182049.33848-1-lucaaamaral@gmail.com/

  virglrenderer (GitLab MRs):
  - MR !1600: macOS build support (merged)
  - MR !1601: posix_spawn worker for macOS (merged)
  - MR !1602: Metal shared memory (R-b by Yiwei Zhang, under review)
    https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1602
  - MR !1603: SOCK_CLOEXEC/MSG_CMSG_CLOEXEC optional (merged)
  - MR !1607: server preparations for macOS process model (merged)
  - MR !1608: Metal vulkan header roll (merged)

I don't think a functional test is practical for CI since it requires
macOS + HVF + MoltenVK + a guest image, but I'm open to suggestions.

Thanks,
Lucas