From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 578C0C48BC4 for ; Thu, 15 Feb 2024 05:04:08 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1raTu3-0002Ev-VJ; Thu, 15 Feb 2024 00:03:19 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1raTu2-0002ED-Ay; Thu, 15 Feb 2024 00:03:18 -0500 Received: from mail-ua1-x929.google.com ([2607:f8b0:4864:20::929]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1raTu0-0000q9-KR; Thu, 15 Feb 2024 00:03:17 -0500 Received: by mail-ua1-x929.google.com with SMTP id a1e0cc1a2514c-7d5c40f874aso189782241.1; Wed, 14 Feb 2024 21:03:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1707973395; x=1708578195; darn=nongnu.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=qOJrSIr+FSrab5/ECJERd9ZL3GlptBROOh4RpOgFt38=; b=QJqnFJRz8S8O5lLT17enYt/QER7wH+psqIQRnnI/DcXI7c+7KTi7G/KK/sLvgf8hCk tw/fKp29s6Xeorxo/UpFmVclOqVeRMRokRuqomIo/aVR+4BP6cwEyt9tekeyQKmSNnk4 eAzm1FZni6Lx00VddZP3cPlCT2GbpVLd8N/AZBvTGxpZwFXygadfh8AjHTRpa3xkVns3 7ucN5rB+FWOxqqKxSyBvk9KDCDaeCgucF8c7cjBiPgQu4cEm4n90pj+4tPYPYnV5kP1Z IXSGvcM7EVjBx7qJZO8N/v6K1isZ02AhE4Gps/q+aaLTaxSfKTU2079MVt1sUejTVwTY zPQA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707973395; x=1708578195; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=qOJrSIr+FSrab5/ECJERd9ZL3GlptBROOh4RpOgFt38=; b=fV3dvYNTDcDK9BMpnjTE8QWjQXRxQpJ8EdFmyFUM09vEbwb2QIJs+l3O374IPZSqWu RrYZf3lrFQMBJ+6c1d1nOP9poGyL4xy/nFPqXBKNjc6H3nvhpe6WxhvJJTtpPV1nrtiR pA8sop40wsPNsg9t0AAa7HXQQq3Me4TgIQiVSe00ZNWgBNHMYbiPgJ0qQavTbRVitOuL rSGwNBCBEo7CvIlyb94LaX/lhMSJhmoStLoVgyK7qmjnjwJbeX+2b+ulBks2zduDVSyI oviC53NxegJw02rdyPj2bFphetQ7k78pUvfsfv25L0Kaj9KNA0LglBxT7WvzFHili68W zdpA== X-Forwarded-Encrypted: i=1; AJvYcCXqImi5Hp/x0Wjpr0fO0ywVhgVFiNyBLGpgPDHdHSQeVqG1XCWwJsG+KlMK56kLvXt+8uptlCLgZIgIypa4tFoB9pmhEOw= X-Gm-Message-State: AOJu0Yz7acJ6o+qbfcvWEBCUzuPEtsYBFGGWoX108i6ffetVTQ3ySMLU jIFaD7/PFX98BdAMUhagc/7ZFUdvlvSUqy7q584SePvEgJhhCqqUMHCxN8WNwoJuTlXX5dW/COz YX5AqXF6EszMm8pOP3VqWgBPZ2o3/mlWe X-Google-Smtp-Source: AGHT+IF+G9D7LlSedKNknaFa0jxaDA21ZNd17AJmx3w0FAXg7bsN8+NH0bRbHSbuQJNZVP9EtezlBee+2LGS7l6e91U= X-Received: by 2002:a05:6102:374c:b0:46d:617b:1bfb with SMTP id u12-20020a056102374c00b0046d617b1bfbmr1185903vst.10.1707973395139; Wed, 14 Feb 2024 21:03:15 -0800 (PST) MIME-Version: 1.0 References: <20240213191736.733334-1-dbarboza@ventanamicro.com> <20240213191736.733334-2-dbarboza@ventanamicro.com> In-Reply-To: <20240213191736.733334-2-dbarboza@ventanamicro.com> From: Alistair Francis Date: Thu, 15 Feb 2024 15:02:49 +1000 Message-ID: Subject: Re: [PATCH 1/6] libqos/virtio.c: init all elems in qvring_indirect_desc_setup() To: Daniel Henrique Barboza Cc: qemu-devel@nongnu.org, 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2607:f8b0:4864:20::929; envelope-from=alistair23@gmail.com; helo=mail-ua1-x929.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 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, T_SCC_BODY_TEXT_LINE=-0.01 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: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Feb 14, 2024 at 5:18=E2=80=AFAM Daniel Henrique Barboza wrote: > > The loop isn't setting the values for the last element. Every other > element is being initialized with addr =3D 0, flags =3D VRING_DESC_F_NEXT > and next =3D i + 1. The last elem is never touched. > > This became a problem when enabling a RISC-V 'virt' libqos machine in > the 'indirect' test of virti-blk-test.c. The 'flags' for the last > element will end up being an odd number (since we didn't touch it). > Being an odd number it will be mistaken by VRING_DESC_F_NEXT, which > happens to be 1. > > Deep into hw/virt/virtio.c, in virtqueue_split_pop(), into > virtqueue_split_read_next_desc(), a check for VRING_DESC_F_NEXT will be > made to see if we're supposed to chain. The code will keep up chaining > in the last element because the unintialized value happens to be odd. > We'll error out right after that because desc->next (which is also > uninitialized) will be >=3D max. A VIRTQUEUE_READ_DESC_ERROR will be > returned, with an error message like this in the stderr: > > qemu-system-riscv64: Desc next is 49391 > > Since we never returned, w'll end up timing out at qvirtio_wait_used_elem= (): > > ERROR:../tests/qtest/libqos/virtio.c:236:qvirtio_wait_used_elem: > assertion failed: (g_get_monotonic_time() - start_time <=3D timeout_u= s) > > The root cause is using unintialized values from guest_alloc() in > qvring_indirect_desc_setup(). There's no guarantee that the memory pages > retrieved will be zeroed, so we can't make assumptions. In fact, commit > 5b4f72f5e8 ("tests/qtest: properly initialise the vring used idx") fixed = a > similar problem stating "It is probably not wise to assume guest memory > is zeroed anyway". I concur. > > Initialize all elems in qvring_indirect_desc_setup(). > > Fixes: f294b029aa ("libqos: Added indirect descriptor support to virtio i= mplementation") > Signed-off-by: Daniel Henrique Barboza Reviewed-by: Alistair Francis Alistair > --- > tests/qtest/libqos/virtio.c | 25 +++++++++++++++++++------ > 1 file changed, 19 insertions(+), 6 deletions(-) > > diff --git a/tests/qtest/libqos/virtio.c b/tests/qtest/libqos/virtio.c > index 410513225f..4f39124eba 100644 > --- a/tests/qtest/libqos/virtio.c > +++ b/tests/qtest/libqos/virtio.c > @@ -280,14 +280,27 @@ QVRingIndirectDesc *qvring_indirect_desc_setup(QTes= tState *qs, QVirtioDevice *d, > indirect->elem =3D elem; > indirect->desc =3D guest_alloc(alloc, sizeof(struct vring_desc) * el= em); > > - for (i =3D 0; i < elem - 1; ++i) { > + for (i =3D 0; i < elem; ++i) { > /* indirect->desc[i].addr */ > qvirtio_writeq(d, qs, indirect->desc + (16 * i), 0); > - /* indirect->desc[i].flags */ > - qvirtio_writew(d, qs, indirect->desc + (16 * i) + 12, > - VRING_DESC_F_NEXT); > - /* indirect->desc[i].next */ > - qvirtio_writew(d, qs, indirect->desc + (16 * i) + 14, i + 1); > + > + /* > + * If it's not the last element of the ring, set > + * the chain (VRING_DESC_F_NEXT) flag and > + * desc->next. Clear the last element - there's > + * no guarantee that guest_alloc() will do it. > + */ > + if (i !=3D elem - 1) { > + /* indirect->desc[i].flags */ > + qvirtio_writew(d, qs, indirect->desc + (16 * i) + 12, > + VRING_DESC_F_NEXT); > + > + /* indirect->desc[i].next */ > + qvirtio_writew(d, qs, indirect->desc + (16 * i) + 14, i + 1)= ; > + } else { > + qvirtio_writew(d, qs, indirect->desc + (16 * i) + 12, 0); > + qvirtio_writew(d, qs, indirect->desc + (16 * i) + 14, 0); > + } > } > > return indirect; > -- > 2.43.0 > >