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bh=dZJpRdzUg+uzEOwmii3gIqvtPsdARGPqDcEANL3u4sw=; b=dolxSw1377kQdOmHvB1j8D1fWxSTr3jOAvFLNkBxE9CDjPojtutLeu1t2UKlmbfpJCJIbD Dckhi0f1F/02jqyG/y+UxvVsyoEsxvgQqtLgkW/PHUbzf1m6F++xgYzkuNRtr6X6osLb/h RWO4YBCn+j05v5R1iaGA/g53UXqPrlA= X-MC-Unique: UOyFyd3UOE2B_ZZFZp4k9g-1 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH v2 3/3] vhost-user: warn when guest RAM is not shared Date: Tue, 25 May 2021 15:28:03 +0100 Message-Id: <20210525142803.125401-4-stefanha@redhat.com> In-Reply-To: <20210525142803.125401-1-stefanha@redhat.com> References: <20210525142803.125401-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com 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=216.205.24.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.371, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, Laurent Vivier , Thomas Huth , "Michael S. Tsirkin" , Stefan Hajnoczi , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Paolo Bonzini Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" Memory regions must be mmap(MAP_SHARED) so that modifications made by the vhost device backend process are visible to QEMU and vice versa. Use the new memory_region_is_mapped_shared() function to check this and print a warning if guest RAM is not shared: qemu-system-x86_64: -device vhost-user-fs-pci,chardev=3Dchar0,tag=3Dmyfs:= warning: Found vhost-user memory region without MAP_SHARED (did you forget= -object memory-*,share=3Don?) qemu-system-x86_64: Failed to read from slave. This warning makes it clear that memory needs to be configured with share=3Don. Without this patch the vhost device is initialized and the device fails with vague error messages caused by inconsistent memory views. The warning should make it easier to troubleshoot QEMU command-lines that lack share=3Don memory. I couldn't figure out how to make this a vhost_dev_init() error, because memory regions aren't necessarily final when it is called. Also, hotplug can add memory regions without MAP_SHARED in the future, so we still need to warn about that. Reported-by: Kevin Wolf Reviewed-by: Marc-Andr=C3=A9 Lureau Signed-off-by: Stefan Hajnoczi --- hw/virtio/vhost-user.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index ee57abe045..42976e6b30 100644 --- a/hw/virtio/vhost-user.c +++ b/hw/virtio/vhost-user.c @@ -2287,11 +2287,23 @@ vhost_user_crypto_close_session(struct vhost_dev *d= ev, uint64_t session_id) static bool vhost_user_mem_section_filter(struct vhost_dev *dev, MemoryRegionSection *section) { - bool result; + /* An fd is required so we can pass it to the device backend process */ + if (memory_region_get_fd(section->mr) < 0) { + return false; + } =20 - result =3D memory_region_get_fd(section->mr) >=3D 0; - - return result; + /* + * It must be mmap(MAP_SHARED) so memory stores from the device backend + * process are visible to us and vice versa. + */ + if (!memory_region_is_mapped_shared(section->mr)) { + static bool warned; + warn_report_once_cond(&warned, "Found vhost-user memory region " + "without MAP_SHARED (did you forget -object " + "memory-*,share=3Don?)"); + return false; + } + return true; } =20 static int vhost_user_get_inflight_fd(struct vhost_dev *dev, --=20 2.31.1