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GET /api/patches/2217816/?format=api
{ "id": 2217816, "url": "http://patchwork.ozlabs.org/api/patches/2217816/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260330151313.66318-1-maxpain@linux.com/", "project": { "id": 14, "url": "http://patchwork.ozlabs.org/api/projects/14/?format=api", "name": "QEMU Development", "link_name": "qemu-devel", "list_id": "qemu-devel.nongnu.org", "list_email": "qemu-devel@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260330151313.66318-1-maxpain@linux.com>", "list_archive_url": null, "date": "2026-03-30T15:13:13", "name": "vhost-user-blk-server: fix size_max=0 breaking Windows guests", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "cf12400384f6be4dff528ac3982a870c76321be2", "submitter": { "id": 93011, "url": "http://patchwork.ozlabs.org/api/people/93011/?format=api", "name": "Max Makarov", "email": "maxpain177@gmail.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260330151313.66318-1-maxpain@linux.com/mbox/", "series": [ { "id": 498066, "url": "http://patchwork.ozlabs.org/api/series/498066/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=498066", "date": "2026-03-30T15:13:13", "name": "vhost-user-blk-server: fix size_max=0 breaking Windows guests", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/498066/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2217816/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2217816/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "X-Original-To": "incoming@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=lEZd9TIv;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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Tsirkin\" <mst@redhat.com>, Kevin Wolf <kwolf@redhat.com>,\n Hanna Reitz <hreitz@redhat.com>, Max Makarov <maxpain@linux.com>", "Subject": "[PATCH] vhost-user-blk-server: fix size_max=0 breaking Windows guests", "Date": "Mon, 30 Mar 2026 18:13:13 +0300", "Message-ID": "<20260330151313.66318-1-maxpain@linux.com>", "X-Mailer": "git-send-email 2.50.1", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "Received-SPF": "pass client-ip=2a00:1450:4864:20::129;\n envelope-from=maxpain177@gmail.com; helo=mail-lf1-x129.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,\n DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001,\n RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001,\n SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no", "X-Spam_action": "no action", "X-Mailman-Approved-At": "Mon, 30 Mar 2026 12:42:36 -0400", "X-BeenThere": "qemu-devel@nongnu.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "qemu development <qemu-devel.nongnu.org>", "List-Unsubscribe": "<https://lists.nongnu.org/mailman/options/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>", "List-Archive": "<https://lists.nongnu.org/archive/html/qemu-devel>", "List-Post": "<mailto:qemu-devel@nongnu.org>", "List-Help": "<mailto:qemu-devel-request@nongnu.org?subject=help>", "List-Subscribe": "<https://lists.nongnu.org/mailman/listinfo/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=subscribe>", "Errors-To": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org", "Sender": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org" }, "content": "The QSD vhost-user-blk export sets size_max=0 in the virtio config,\nbut the vhost-user-blk frontend unconditionally advertises\nVIRTIO_BLK_F_SIZE_MAX. This creates a spec-violating state: the\nfeature bit tells the guest that size_max is valid, but the value\nis 0.\n\nNative virtio-blk-pci does not advertise VIRTIO_BLK_F_SIZE_MAX when\nsize_max=0, so guests never see this contradiction there.\n\nThe Windows viostor driver trusts the feature bit and uses size_max=0\nin its MaximumTransferLength calculation, producing malformed\nscatter-gather requests. The disk appears completely empty to Windows\n(no GPT, no partitions in diskpart), causing INACCESSIBLE_BOOT_DEVICE\nBSOD. Linux is unaffected because its virtio_blk driver falls back to\nPAGE_SIZE when size_max=0.\n\nSet size_max to 4096 (PAGE_SIZE) to provide a valid segment size limit\nthat matches what Linux assumes as a fallback. This fixes Windows\nServer 2025 (and likely all Windows versions) booting from\nvhost-user-blk.\n\nBuglink: https://github.com/spdk/spdk/issues/3199\nBuglink: https://github.com/virtio-win/kvm-guest-drivers-windows/issues/692\nSigned-off-by: Max Makarov <maxpain@linux.com>\n---\n block/export/vhost-user-blk-server.c | 2 +-\n 1 file changed, 1 insertion(+), 1 deletion(-)", "diff": "diff --git a/block/export/vhost-user-blk-server.c b/block/export/vhost-user-blk-server.c\nindex e89422b..827502d 100644\n--- a/block/export/vhost-user-blk-server.c\n+++ b/block/export/vhost-user-blk-server.c\n@@ -240,7 +240,7 @@ vu_blk_initialize_config(BlockDriverState *bs,\n config->capacity =\n cpu_to_le64(bdrv_getlength(bs) >> VIRTIO_BLK_SECTOR_BITS);\n config->blk_size = cpu_to_le32(blk_size);\n- config->size_max = cpu_to_le32(0);\n+ config->size_max = cpu_to_le32(4096);\n config->seg_max = cpu_to_le32(128 - 2);\n config->min_io_size = cpu_to_le16(1);\n config->opt_io_size = cpu_to_le32(1);\n", "prefixes": [] }