Re: [Xen-devel] [PATCH v5 01/16] x86/mm: skip incrementing mfn if it is not a valid mfn

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.03.18 at 19:31, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 14/03/18 18:19, julien.grall@xxxxxxx wrote:
>> From: Wei Liu <wei.liu2@xxxxxxxxxx>
>>
>> The function is called to fill in page table entries in
>> populate_pt_range. Skip incrementing mfn if it is invalid.
>>
>> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> 
> Remind me what the purpose of this patch is?

This is in preparation to switch callers to pass INVALID_MFN
instead of zero for non-present mappings. The incrementing
from zero was wrong here already (but couldn't be as easily
avoided, to not cause problems with possible legitimate uses of
MFN 0), but incrementing (and wrapping) from INVALID_MFN is
(imo) even worse, which is why I had asked the conversion to
INVALID_MFN to not be done without this change.

Jan


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