[v1] virtio,pci,pc: features, fixes

[PULL 24/51] virtio/vhost: don't consider non-MAP_SHARED regions public

Michael S. Tsirkin posted 51 patches 3 days, 21 hours ago

Diff against v1 v2
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Maintainers: "Gonglei (Arei)" <arei.gonglei@huawei.com>, zhenwei pi <zhenwei.pi@linux.dev>, "Michael S. Tsirkin" <mst@redhat.com>, Stefano Garzarella <sgarzare@redhat.com>, Pierrick Bouvier <pierrick.bouvier@linaro.org>, Igor Mammedov <imammedo@redhat.com>, Ani Sinha <anisinha@redhat.com>, Dongjiu Geng <gengdongjiu1@gmail.com>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Raphael Norwitz <raphael@enfabrica.net>, Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>, Jonathan Cameron <jonathan.cameron@huawei.com>, Fan Ni <fan.ni@samsung.com>, Albert Esteve <aesteve@redhat.com>, "Alex Bennée" <alex.bennee@linaro.org>, Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>, Dmitry Osipenko <dmitry.osipenko@collabora.com>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <richard.henderson@linaro.org>, Eduardo Habkost <eduardo@habkost.net>, Jason Wang <jasowang@redhat.com>, Yi Liu <yi.l.liu@intel.com>, "Clément Mathieu--Drif" <clement.mathieu--drif@eviden.com>, BALATON Zoltan <balaton@eik.bme.hu>, "Cédric Le Goater" <clg@kaod.org>, Peter Maydell <peter.maydell@linaro.org>, Steven Lee <steven_lee@aspeedtech.com>, Troy Lee <leetroy@gmail.com>, Jamin Lin <jamin_lin@aspeedtech.com>, Andrew Jeffery <andrew@codeconstruct.com.au>, Joel Stanley <joel@jms.id.au>, Andrey Smirnov <andrew.smirnov@gmail.com>, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Aurelien Jarno <aurelien@aurel32.net>, Nicholas Piggin <npiggin@gmail.com>, Aditya Gupta <adityag@linux.ibm.com>, Glenn Miles <milesg@linux.ibm.com>, Bernhard Beschow <shentey@gmail.com>, "Hervé Poussineau" <hpoussin@reactos.org>, Elena Ufimtseva <elena.ufimtseva@oracle.com>, Jagannathan Raman <jag.raman@oracle.com>, Paul Burton <paulburton@kernel.org>, Aleksandar Rikalo <arikalo@gmail.com>, "Eugenio Pérez" <eperezma@redhat.com>, Haixu Cui <quic_haixcui@quicinc.com>, Peter Xu <peterx@redhat.com>, Fabiano Rosas <farosas@suse.de>, Cornelia Huck <cohuck@redhat.com>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>, Laurent Vivier <lvivier@redhat.com>

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[PULL 24/51] virtio/vhost: don't consider non-MAP_SHARED regions public

Posted by Michael S. Tsirkin 3 days, 21 hours ago

From: Daniil Tatianin <d-tatianin@yandex-team.ru>

Just having a file descriptor is not enough to consider a memory region
public. If QEMU didn't map it as MAP_SHARED (in case of share=off), guest
writes to this region won't be visible to the vhost-user backend, thus
causing it to read all zeroes or garbage. Make sure we don't pass such
regions and include that to our definition of what a private region is.

Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Fixes: 552b25229c ("vhost: Rework memslot filtering and fix "used_memslot" tracking")
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20251113085842.323745-1-d-tatianin@yandex-team.ru>
---
 hw/virtio/vhost.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 31e9704cdc..c6a5928cb1 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -592,11 +592,13 @@ static bool vhost_section(struct vhost_dev *dev, MemoryRegionSection *section)
         /*
          * Some backends (like vhost-user) can only handle memory regions
          * that have an fd (can be mapped into a different process). Filter
-         * the ones without an fd out, if requested.
-         *
-         * TODO: we might have to limit to MAP_SHARED as well.
+         * the ones without an fd out, if requested. Also make sure that
+         * this region is mapped as shared so that the vhost backend can
+         * observe modifications to this region, otherwise we consider it
+         * private.
          */
-        if (memory_region_get_fd(section->mr) < 0 &&
+        if ((memory_region_get_fd(section->mr) < 0 ||
+            !qemu_ram_is_shared(section->mr->ram_block)) &&
             dev->vhost_ops->vhost_backend_no_private_memslots &&
             dev->vhost_ops->vhost_backend_no_private_memslots(dev)) {
             trace_vhost_reject_section(mr->name, 2);
-- 
MST