Re: [Xen-devel] [PATCH for 4.6 v3 4/5] libxc: don't populate same pfn more than once in populate_pfns

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.09.15 at 22:05, <wei.liu2@xxxxxxxxxx> wrote:
> The original implementation of populate_pfns didn't consider the same
> pfn can be present multiple times in the array. The mechanism to prevent
> populating the same pfn multiple times only worked if the recurring pfn
> appeared in different batches.
> 
> This bug is discovered by Linux 4.1 32 bit kernel save / restore test,
> which has several ptes pointing to same pfn, which results in an array
> containing recurring pfn.

Since you must have debugged this, and since the bisector appears
to have fingered a patch of mine on the Linux side which triggered
this, would you mind explaining this a little more? In particular I'm
worried that this may point out some other bug in Linux, as in the
context of the change there - dealing with the 1:1 mapping - I can't
see a legitimate reason for multiple PTEs to reference the same PFN.

Thanks, Jan


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