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Tue, 13 Feb 2024 11:17:50 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCVk4Lp/HtZQs71C8KTcWkksSToD+9Geq3ZSiuIXR83KvKkeXYfd1Sh+Pib3fv9Eo9qn3JBf7CN8fq29rDjKKhXeZS083U9wIw8rCgtB8QKz5gez25gxXjxrznOMTencChU2kdJ7yOe3PBzWaV5yelFQOsbwFAH4soLVnXPiuvullB8KXoTeiMuO/a5ePdDkb/KBq/b7F97GBCaBsZKyXTwbZ6i+jgkP72NbRBp7f6rkMugNHIs+oDuE5Mjrwi+zdUsFulR8imQ/hNA6C88KZ9PsqAId5A8qyY/aZ0KPmtZdIgokNrQuOEOFRpmC9Ufz/n7U0I1hDTjp8XGxuFxaVEnzTSab+gUETnqPAqpsv2agIR8qFvbBQ2fQD+Ywd0JmCH4G/0ffHaoSc/do From: Daniel Henrique Barboza To: qemu-devel@nongnu.org Cc: qemu-riscv@nongnu.org, alistair.francis@wdc.com, bmeng@tinylab.org, liwei1518@gmail.com, zhiwei_liu@linux.alibaba.com, palmer@rivosinc.com, thuth@redhat.com, lvivier@redhat.com, pbonzini@redhat.com, ajones@ventanamicro.com, alex.bennee@linaro.org, Daniel Henrique Barboza Subject: [PATCH 2/6] libqos/virtio.c: fix 'avail_event' offset in qvring_init() Date: Tue, 13 Feb 2024 16:17:32 -0300 Message-ID: <20240213191736.733334-3-dbarboza@ventanamicro.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240213191736.733334-1-dbarboza@ventanamicro.com> References: <20240213191736.733334-1-dbarboza@ventanamicro.com> 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=2607:f8b0:4864:20::62a; envelope-from=dbarboza@ventanamicro.com; helo=mail-pl1-x62a.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: 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 @ventanamicro.com) X-ZM-MESSAGEID: 1707851925065100005 Content-Type: text/plain; charset="utf-8" In qvring_init() we're writing vq->used->avail_event at "vq->used + 2 + array_size". The struct pointed by vq->used is, from virtio_ring.h Linux header): * // A ring of used descriptor heads with free-running index. * __virtio16 used_flags; * __virtio16 used_idx; * struct vring_used_elem used[num]; * __virtio16 avail_event_idx; So 'flags' is the word right at vq->used. 'idx' is vq->used + 2. We need to skip 'used_idx' by adding + 2 bytes, and then sum the vector size, to reach avail_event_idx. An example on how to properly access this field can be found in qvirtqueue_kick(): avail_event =3D qvirtio_readw(d, qts, vq->used + 4 + sizeof(struct vring_used_elem) * vq->size); This error was detected when enabling the RISC-V 'virt' libqos machine. The 'idx' test from vhost-user-blk-test.c errors out with a timeout in qvirtio_wait_used_elem(). The timeout happens because when processing the first element, 'avail_event' is read in qvirtqueue_kick() as non-zero because we didn't initialize it properly (and the memory at that point happened to be non-zero). 'idx' is 0. All of this makes this condition fail because "idx - avail_event" will overflow and be non-zero: /* < 1 because we add elements to avail queue one by one */ if ((flags & VRING_USED_F_NO_NOTIFY) =3D=3D 0 && (!vq->event || (uint16_t)(idx-avail_event) < 1)) { d->bus->virtqueue_kick(d, vq); } As a result the virtqueue is never kicked and we'll timeout waiting for it. Fixes: 1053587c3f ("libqos: Added EVENT_IDX support") Signed-off-by: Daniel Henrique Barboza Reviewed-by: Alistair Francis Reviewed-by: Thomas Huth --- tests/qtest/libqos/virtio.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tests/qtest/libqos/virtio.c b/tests/qtest/libqos/virtio.c index 4f39124eba..82a6e122bf 100644 --- a/tests/qtest/libqos/virtio.c +++ b/tests/qtest/libqos/virtio.c @@ -265,7 +265,7 @@ void qvring_init(QTestState *qts, const QGuestAllocator= *alloc, QVirtQueue *vq, /* vq->used->idx */ qvirtio_writew(vq->vdev, qts, vq->used + 2, 0); /* vq->used->avail_event */ - qvirtio_writew(vq->vdev, qts, vq->used + 2 + + qvirtio_writew(vq->vdev, qts, vq->used + 4 + sizeof(struct vring_used_elem) * vq->size, 0); } =20 --=20 2.43.0