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Tsirkin" , Kevin Wolf , Hanna Reitz , Max Makarov Subject: [PATCH v2] vhost-user-blk: do not force VIRTIO_BLK_F_SIZE_MAX Date: Tue, 31 Mar 2026 16:47:21 +0300 Message-ID: <20260331134721.96047-1-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::12f; envelope-from=maxpain177@gmail.com; helo=mail-lf1-x12f.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=ham 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: 1774964871511158500 Content-Type: text/plain; charset="utf-8" vhost_user_blk_get_features() unconditionally advertises VIRTIO_BLK_F_SIZE_MAX regardless of what the backend reports in its config. The built-in QSD vhost-user-blk backend sets size_max=3D0, creating a contradictory state where the feature bit tells the guest that size_max is valid but the value is zero. The in-process virtio-blk device does not advertise VIRTIO_BLK_F_SIZE_MAX (it also sets size_max=3D0 in config), so guests never see this contradiction with native virtio-blk. Linux tolerates size_max=3D0 because blk_validate_limits() silently corrects max_segment_size=3D0 to BLK_MAX_SEGMENT_SIZE (65536). Windows viostor, however, trusts the feature bit and uses the raw size_max=3D0 in its scatter-gather calculations, producing zero-length segments that hang I/O. The disk appears empty to Windows (no GPT, no partitions), causing INACCESSIBLE_BOOT_DEVICE. Stop force-adding VIRTIO_BLK_F_SIZE_MAX in the frontend. The feature remains in user_feature_bits[], so backends that properly advertise it with a valid config value will still work. Signed-off-by: Max Makarov --- v2: - Remove the VIRTIO_BLK_F_SIZE_MAX feature bit from the frontend instead of setting size_max=3D4096 in the backend config [Kevin Wolf] - Fix incorrect claim about Linux PAGE_SIZE fallback - Drop unrelated Buglink tags --- hw/block/vhost-user-blk.c | 1 - 1 file changed, 1 deletion(-) diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c index c151e83..7ba6562 100644 --- a/hw/block/vhost-user-blk.c +++ b/hw/block/vhost-user-blk.c @@ -273,7 +273,6 @@ static uint64_t vhost_user_blk_get_features(VirtIODevic= e *vdev, VHostUserBlk *s =3D VHOST_USER_BLK(vdev); =20 /* Turn on pre-defined features */ - virtio_add_feature(&features, VIRTIO_BLK_F_SIZE_MAX); virtio_add_feature(&features, VIRTIO_BLK_F_SEG_MAX); virtio_add_feature(&features, VIRTIO_BLK_F_GEOMETRY); virtio_add_feature(&features, VIRTIO_BLK_F_TOPOLOGY); --=20 2.53.0