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Re: [Qemu-devel] [RFC/BUG] xen-mapcache: buggy invalidate map cache?

From: Stefano Stabellini
Subject: Re: [Qemu-devel] [RFC/BUG] xen-mapcache: buggy invalidate map cache?
Date: Mon, 10 Apr 2017 12:04:15 -0700 (PDT)
User-agent: Alpine 2.10 (DEB 1266 2009-07-14)

On Mon, 10 Apr 2017, hrg wrote:
> On Sun, Apr 9, 2017 at 11:55 PM, hrg <address@hidden> wrote:
> > On Sun, Apr 9, 2017 at 11:52 PM, hrg <address@hidden> wrote:
> >> Hi,
> >>
> >> In xen_map_cache_unlocked(), map to guest memory maybe in entry->next
> >> instead of first level entry (if map to rom other than guest memory
> >> comes first), while in xen_invalidate_map_cache(), when VM ballooned
> >> out memory, qemu did not invalidate cache entries in linked
> >> list(entry->next), so when VM balloon back in memory, gfns probably
> >> mapped to different mfns, thus if guest asks device to DMA to these
> >> GPA, qemu may DMA to stale MFNs.
> >>
> >> So I think in xen_invalidate_map_cache() linked lists should also be
> >> checked and invalidated.
> >>
> >> What’s your opinion? Is this a bug? Is my analyze correct?

Yes, you are right. We need to go through the list for each element of
the array in xen_invalidate_map_cache. Can you come up with a patch?

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