ci: Add virtio-villain test suite job

Add a GitHub Actions job that runs the virtio-villain suite against
cloud-hypervisor, giving continuous coverage of how the virtio device
model responds to guest input that violates the driver side rules of
the virtio specification. The suite drives the device model from the
guest side with out of spec virtqueue input, malformed descriptor
chains, transport register abuse, and device specific requests, then
checks that each violation is handled without crashing the device or
leaving it wedged. This makes a class of guest triggered failures a
signal that shows up on every relevant change rather than found by
chance.

The job builds cloud-hypervisor with the kvm feature, clones
virtio-villain at a pinned tag, builds its initramfs, and runs the
tests in short lived VMs, rerunning a wedged batch in isolation so a
failure is attributed to the offending test. Results reach the run
summary page, and the JUnit report plus per test logs upload as an
artifact. The compiled harness, the initramfs, and the fetched guest
kernel are cached under the resolved villain commit, so an unchanged
pin skips the rebuild.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
Assisted-by: Claude:Opus-4.8
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

.github/workflows/ci.yaml

@@ -846,6 +846,84 @@ jobs:
   #     - name: Run rate-limiter integration tests
   #       timeout-minutes: 20
   #       run: scripts/dev_cli.sh tests --integration-rate-limiter
+  virtio-villain:
+    name: virtio-villain
+    needs: [preflight, dco, quality, build]
+    if: needs.preflight.outputs.full == 'true'
+    timeout-minutes: 60
+    runs-on: ubuntu-latest
+    env:
+      VILLAIN_REPO: https://github.com/weltling/virtio-villain.git
+      VILLAIN_REF: v0.5.0
+    steps:
+      - name: Code checkout
+        uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+      - name: Verify KVM is available
+        run: |
+          set -eufo pipefail
+          test -e /dev/kvm || { echo "::error::/dev/kvm missing on runner"; exit 1; }
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+      - name: Install dependencies
+        run: |
+          set -eufo pipefail
+          sudo apt-get update
+          sudo apt-get install -y musl-tools cpio gzip python3
+          sudo apt-get install -y virtiofsd || true
+      - name: Build cloud-hypervisor (kvm)
+        run: cargo build --locked --release --bin cloud-hypervisor --no-default-features --features kvm
+      - name: Clone virtio-villain
+        id: villain-src
+        run: |
+          set -eufo pipefail
+          git clone "$VILLAIN_REPO" virtio-villain
+          git -C virtio-villain checkout "$VILLAIN_REF"
+          echo "sha=$(git -C virtio-villain rev-parse HEAD)" >> "$GITHUB_OUTPUT"
+      - name: Cache virtio-villain build
+        id: villain-cache
+        uses: actions/cache@v4
+        with:
+          path: virtio-villain/target
+          key: virtio-villain-${{ runner.os }}-${{ runner.arch }}-${{ steps.villain-src.outputs.sha }}
+      - name: Build virtio-villain initramfs
+        if: steps.villain-cache.outputs.cache-hit != 'true'
+        run: make -C virtio-villain -j"$(nproc)" initramfs
+      - name: Run virtio-villain suite
+        working-directory: virtio-villain
+        run: |
+          set -eufo pipefail
+          mkdir -p villain-logs
+          sudo ./run \
+            --vmm "${GITHUB_WORKSPACE}/target/release/cloud-hypervisor" \
+            --blk-queues 2 --net-queues 2 --cpus 2 --memory 256M \
+            --order=fast \
+            --jobs 4 --batch 10 --timeout 45 --log-dir villain-logs \
+            --format junit --output villain-logs/results.xml \
+            | tee villain-logs/run.out
+      - name: Publish results to run summary
+        if: always()
+        working-directory: virtio-villain
+        run: |
+          set -eufo pipefail
+          {
+            echo '## virtio-villain'
+            echo '```'
+            if [ -f villain-logs/run.out ]; then
+              sed -n '/tests passed/,$p' villain-logs/run.out
+            else
+              echo 'no results (suite did not produce output)'
+            fi
+            echo '```'
+          } >> "$GITHUB_STEP_SUMMARY"
+      - name: Upload virtio-villain logs
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: virtio-villain-logs
+          path: virtio-villain/villain-logs
+          if-no-files-found: ignore
   # The single required-status check. Branch protection requires this one job.
   all-green:
     name: all-green