From: "Michael S. Tsirkin" <mst@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>,
qemu-stable@nongnu.org, qemu-devel@nongnu.org,
Stefan Hajnoczi <stefanha@redhat.com>,
David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [Qemu-devel] [PATCH-for-4.1 v2 3/3] virtio-balloon: reset pbp on device resets
Date: Wed, 17 Jul 2019 07:29:19 -0400 [thread overview]
Message-ID: <20190717072551-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <0828606b-4cdf-63ea-9211-dc5905b00f4b@redhat.com>
On Wed, Jul 17, 2019 at 01:06:29PM +0200, David Hildenbrand wrote:
> On 17.07.19 12:48, Michael S. Tsirkin wrote:
> > On Wed, Jul 17, 2019 at 12:35:50PM +0200, David Hildenbrand wrote:
> >> When a guest reboots (ordinary reboots, but also via kexec), it will
> >> happily reuse any system memory, including previously inflated memory.
> >>
> >> We could have tracking data for a pbp (PartiallyBalloonedPage). It could
> >> happen that a new inflation request from the guest will result in a
> >> discard of such a pbp, although the guest is (again) reusing some
> >> memory.
> >>
> >> We should reset the pbp on any device resets.
> >>
> >> Fixes: ed48c59875b6 ("virtio-balloon: Safely handle BALLOON_PAGE_SIZE <
> >> host page size")
> >> Cc: qemu-stable@nongnu.org #v4.0.0
> >> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> >> Cc: David Gibson <david@gibson.dropbear.id.au>
> >> Cc: Michael S. Tsirkin <mst@redhat.com>
> >> Cc: Igor Mammedov <imammedo@redhat.com>
> >> Signed-off-by: David Hildenbrand <david@redhat.com>
> >
> > Can't something else remove a ramblock besides a reset?
>
> Yes, however this patch is not about ramblocks getting removed.
>
> Take a close look, "balloon->pbp->rb" is only used as a token, it is
> never used besides for comparisons.
You are right but that's still not safe :)
E.g. the bit we are going to set could be out of range of the bitmap because
the backing page size changed.
> --
>
> Thanks,
>
> David / dhildenb
next prev parent reply other threads:[~2019-07-17 11:29 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-17 10:35 [Qemu-devel] [PATCH-for-4.1 v2 0/3] virtio-balloon: fixes for PartialBalloonedPage David Hildenbrand
2019-07-17 10:35 ` [Qemu-devel] [PATCH-for-4.1 v2 1/3] virtio-balloon: fix QEMU crashes on pagesize > BALLOON_PAGE_SIZE David Hildenbrand
2019-07-18 3:50 ` David Gibson
2019-07-18 11:50 ` David Hildenbrand
2019-07-17 10:35 ` [Qemu-devel] [PATCH-for-4.1 v2 2/3] virtio-balloon: fix memory leak on unrealize() David Hildenbrand
2019-07-18 3:51 ` David Gibson
2019-07-17 10:35 ` [Qemu-devel] [PATCH-for-4.1 v2 3/3] virtio-balloon: reset pbp on device resets David Hildenbrand
2019-07-17 10:48 ` Michael S. Tsirkin
2019-07-17 11:06 ` David Hildenbrand
2019-07-17 11:29 ` Michael S. Tsirkin [this message]
2019-07-17 11:32 ` David Hildenbrand
2019-07-18 3:52 ` David Gibson
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