Michael S. Tsirkin
2020-Jul-10 11:31 UTC
[PATCH] virtio_balloon: clear modern features under legacy
Page reporting features were never supported by legacy hypervisors.
Supporting them poses a problem: should we use native endian-ness (like
current code assumes)? Or little endian-ness like the virtio spec says?
Rather than try to figure out, and since results of
incorrect endian-ness are dire, let's just block this configuration.
Cc: stable at vger.kernel.org
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
drivers/virtio/virtio_balloon.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 5d4b891bf84f..b9bc03345157 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -1107,6 +1107,15 @@ static int virtballoon_restore(struct virtio_device
*vdev)
static int virtballoon_validate(struct virtio_device *vdev)
{
+ /*
+ * Legacy devices never specified how modern features should behave.
+ * E.g. which endian-ness to use? Better not to assume anything.
+ */
+ if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
+ __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT);
+ __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
+ __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
+ }
/*
* Inform the hypervisor that our pages are poisoned or
* initialized. If we cannot do that then we should disable
--
MST
David Hildenbrand
2020-Jul-10 11:32 UTC
[PATCH] virtio_balloon: clear modern features under legacy
On 10.07.20 13:31, Michael S. Tsirkin wrote:> Page reporting features were never supported by legacy hypervisors. > Supporting them poses a problem: should we use native endian-ness (like > current code assumes)? Or little endian-ness like the virtio spec says? > Rather than try to figure out, and since results of > incorrect endian-ness are dire, let's just block this configuration. > > Cc: stable at vger.kernel.org > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > --- > drivers/virtio/virtio_balloon.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 5d4b891bf84f..b9bc03345157 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -1107,6 +1107,15 @@ static int virtballoon_restore(struct virtio_device *vdev) > > static int virtballoon_validate(struct virtio_device *vdev) > { > + /* > + * Legacy devices never specified how modern features should behave. > + * E.g. which endian-ness to use? Better not to assume anything. > + */ > + if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) { > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT); > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); > + } > /* > * Inform the hypervisor that our pages are poisoned or > * initialized. If we cannot do that then we should disable >Very right Acked-by: David Hildenbrand <david at redhat.com> -- Thanks, David / dhildenb
Alexander Duyck
2020-Jul-10 16:13 UTC
[PATCH] virtio_balloon: clear modern features under legacy
On Fri, Jul 10, 2020 at 4:31 AM Michael S. Tsirkin <mst at redhat.com> wrote:> > Page reporting features were never supported by legacy hypervisors. > Supporting them poses a problem: should we use native endian-ness (like > current code assumes)? Or little endian-ness like the virtio spec says? > Rather than try to figure out, and since results of > incorrect endian-ness are dire, let's just block this configuration. > > Cc: stable at vger.kernel.org > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>So I am not sure about the patch description. In the case of page poison and free page reporting I don't think we are defining anything that doesn't already have a definition of how to use in legacy. Specifically the virtio_balloon_config is already defined as having all fields as little endian in legacy mode, and there is a definition for all of the fields in a virtqueue and how they behave in legacy mode. As far as I can see the only item that may be an issue is the command ID being supplied via the virtqueue for free page hinting, which appears to be in native endian-ness. Otherwise it would have fallen into the same category since it is making use of virtio_balloon_config and a virtqueue for supplying the page location and length.> --- > drivers/virtio/virtio_balloon.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 5d4b891bf84f..b9bc03345157 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -1107,6 +1107,15 @@ static int virtballoon_restore(struct virtio_device *vdev) > > static int virtballoon_validate(struct virtio_device *vdev) > { > + /* > + * Legacy devices never specified how modern features should behave. > + * E.g. which endian-ness to use? Better not to assume anything. > + */ > + if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) { > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT); > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); > + } > /* > * Inform the hypervisor that our pages are poisoned or > * initialized. If we cannot do that then we should disableThe patch content itself I am fine with since odds are nobody would expect to use these features with a legacy device. Acked-by: Alexander Duyck <alexander.h.duyck at linux.intel.com>
Michael S. Tsirkin
2020-Jul-12 15:09 UTC
[PATCH] virtio_balloon: clear modern features under legacy
On Fri, Jul 10, 2020 at 09:13:41AM -0700, Alexander Duyck wrote:> On Fri, Jul 10, 2020 at 4:31 AM Michael S. Tsirkin <mst at redhat.com> wrote: > > > > Page reporting features were never supported by legacy hypervisors. > > Supporting them poses a problem: should we use native endian-ness (like > > current code assumes)? Or little endian-ness like the virtio spec says? > > Rather than try to figure out, and since results of > > incorrect endian-ness are dire, let's just block this configuration. > > > > Cc: stable at vger.kernel.org > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > > So I am not sure about the patch description. In the case of page > poison and free page reporting I don't think we are defining anything > that doesn't already have a definition of how to use in legacy. > Specifically the virtio_balloon_config is already defined as having > all fields as little endian in legacy mode, and there is a definition > for all of the fields in a virtqueue and how they behave in legacy > mode. > > As far as I can see the only item that may be an issue is the command > ID being supplied via the virtqueue for free page hinting, which > appears to be in native endian-ness. Otherwise it would have fallen > into the same category since it is making use of virtio_balloon_config > and a virtqueue for supplying the page location and length.So as you point out correctly balloon spec says all fields are little endian. Fair enough. Problem is when virtio 1 is not negotiated, then this is not what the driver assumes for any except a handlful of fields. But yes it mostly works out. For example: static void update_balloon_size(struct virtio_balloon *vb) { u32 actual = vb->num_pages; /* Legacy balloon config space is LE, unlike all other devices. */ if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1)) actual = (__force u32)cpu_to_le32(actual); virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual, &actual); } this is LE even without VIRTIO_F_VERSION_1, so matches spec. /* Start with poison val of 0 representing general init */ __u32 poison_val = 0; /* * Let the hypervisor know that we are expecting a * specific value to be written back in balloon pages. */ if (!want_init_on_free()) memset(&poison_val, PAGE_POISON, sizeof(poison_val)); virtio_cwrite(vb->vdev, struct virtio_balloon_config, poison_val, &poison_val); actually this writes a native endian-ness value. All bytes happen to be the same though, and host only cares about 0 or non 0 ATM. As you say correctly the command id is actually assumed native endian: static u32 virtio_balloon_cmd_id_received(struct virtio_balloon *vb) { if (test_and_clear_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID, &vb->config_read_bitmap)) virtio_cread(vb->vdev, struct virtio_balloon_config, free_page_hint_cmd_id, &vb->cmd_id_received_cache); return vb->cmd_id_received_cache; } So guest assumes native, host assumes LE.> > --- > > drivers/virtio/virtio_balloon.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > > index 5d4b891bf84f..b9bc03345157 100644 > > --- a/drivers/virtio/virtio_balloon.c > > +++ b/drivers/virtio/virtio_balloon.c > > @@ -1107,6 +1107,15 @@ static int virtballoon_restore(struct virtio_device *vdev) > > > > static int virtballoon_validate(struct virtio_device *vdev) > > { > > + /* > > + * Legacy devices never specified how modern features should behave. > > + * E.g. which endian-ness to use? Better not to assume anything. > > + */ > > + if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) { > > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT); > > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); > > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); > > + } > > /* > > * Inform the hypervisor that our pages are poisoned or > > * initialized. If we cannot do that then we should disable > > The patch content itself I am fine with since odds are nobody would > expect to use these features with a legacy device. > > Acked-by: Alexander Duyck <alexander.h.duyck at linux.intel.com>Hmm so now you pointed out it's just cmd id, maybe I should just fix it instead? what do you say? -- MST
Jason Wang
2020-Jul-13 03:36 UTC
[PATCH] virtio_balloon: clear modern features under legacy
On 2020/7/10 ??7:31, Michael S. Tsirkin wrote:> Page reporting features were never supported by legacy hypervisors. > Supporting them poses a problem: should we use native endian-ness (like > current code assumes)? Or little endian-ness like the virtio spec says? > Rather than try to figure out, and since results of > incorrect endian-ness are dire, let's just block this configuration. > > Cc: stable at vger.kernel.org > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > --- > drivers/virtio/virtio_balloon.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 5d4b891bf84f..b9bc03345157 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -1107,6 +1107,15 @@ static int virtballoon_restore(struct virtio_device *vdev) > > static int virtballoon_validate(struct virtio_device *vdev) > { > + /* > + * Legacy devices never specified how modern features should behave. > + * E.g. which endian-ness to use? Better not to assume anything. > + */ > + if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) { > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT); > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); > + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); > + } > /* > * Inform the hypervisor that our pages are poisoned or > * initialized. If we cannot do that then we should disableAcked-by: Jason Wang <jasowang at redhat.com>
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