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Re: [Qemu-devel] [PATCH-for-4.1 v2 3/3] virtio-balloon: reset pbp on dev

From: David Hildenbrand
Subject: Re: [Qemu-devel] [PATCH-for-4.1 v2 3/3] virtio-balloon: reset pbp on device resets
Date: Wed, 17 Jul 2019 13:06:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2

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: address@hidden #v4.0.0
>> Cc: Stefan Hajnoczi <address@hidden>
>> Cc: David Gibson <address@hidden>
>> Cc: Michael S. Tsirkin <address@hidden>
>> Cc: Igor Mammedov <address@hidden>
>> Signed-off-by: David Hildenbrand <address@hidden>
> 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.



David / dhildenb

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