Re: [Xen-devel] [PATCH 0/2] MMIO emulation fixes

[Olaf Hering <olaf@xxxxxxxxx>]

On Wed, Aug 29, Andrew Cooper wrote:

> Architecturally speaking, handing #MC back is probably the closest we
> can get to sensible behaviour, but it is still a bug that Linux is
> touching the ballooned out page in the first place.

Well, the issue is that a read crosses a page boundary. If that would be
forbidden, load_unaligned_zeropad() would not exist. It can not know
what is in the following page. And such page crossing happens also in
the unballooned case. Sadly I can not trigger the reported NFS bug
myself. But it can be enforced by ballooning enough pages so that an
allocated readdir reply eventually is right in front of a ballooned
page.

Olaf

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