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Tsirkin" , Kevin Wolf , Hanna Reitz , Max Makarov Subject: [PATCH] vhost-user-blk-server: do not advertise VIRTIO_BLK_F_SIZE_MAX with size_max=0 Date: Tue, 31 Mar 2026 18:28:56 +0300 Message-ID: <20260331152856.1802-1-maxpain@linux.com> X-Mailer: git-send-email 2.50.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2a00:1450:4864:20::12c; envelope-from=maxpain177@gmail.com; helo=mail-lf1-x12c.google.com X-Spam_score_int: -17 X-Spam_score: -1.8 X-Spam_bar: - X-Spam_report: (-1.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @gmail.com) X-ZM-MESSAGEID: 1774970995593154100 Content-Type: text/plain; charset="utf-8" The QSD vhost-user-blk backend advertises VIRTIO_BLK_F_SIZE_MAX but sets size_max=3D0 in config, creating a contradictory state. The feature bit tells the guest that size_max is valid, but the value is zero. Windows viostor trusts the feature bit, reads size_max=3D0, and uses it in scatter-gather calculations producing zero-length segments that hang I/O. The disk appears empty (no GPT, no partitions), causing INACCESSIBLE_BOOT_DEVICE BSOD. Linux tolerates this because blk_validate_limits() silently corrects max_segment_size=3D0 to BLK_MAX_SEGMENT_SIZE (65536). This affects any VMM using QSD as a vhost-user-blk backend (QEMU, Cloud Hypervisor, etc.), since both pass through SIZE_MAX from the backend to the guest via feature intersection. Remove VIRTIO_BLK_F_SIZE_MAX from the backend feature bits. The size_max config field remains zero but is now ignored by guests since the feature is not negotiated. Signed-off-by: Max Makarov --- block/export/vhost-user-blk-server.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/export/vhost-user-blk-server.c b/block/export/vhost-user= -blk-server.c index e89422b..b6b03b0 100644 --- a/block/export/vhost-user-blk-server.c +++ b/block/export/vhost-user-blk-server.c @@ -119,7 +119,7 @@ static uint64_t vu_blk_get_features(VuDev *dev) uint64_t features; VuServer *server =3D container_of(dev, VuServer, vu_dev); VuBlkExport *vexp =3D container_of(server, VuBlkExport, vu_server); - features =3D 1ull << VIRTIO_BLK_F_SIZE_MAX | + features =3D 1ull << VIRTIO_BLK_F_SEG_MAX | 1ull << VIRTIO_BLK_F_TOPOLOGY | 1ull << VIRTIO_BLK_F_BLK_SIZE | --=20 2.50.1 (Apple Git-155)