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

[George Dunlap <dunlapg@xxxxxxxxx>]

On Thu, Mar 15, 2018 at 12:16 PM, Andrew Cooper
<andrew.cooper3@xxxxxxxxxx> wrote:
> On 15/03/18 07:52, Jan Beulich wrote:
>>>>> 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.
>
> Yes.  My reply was a (clearly too) thinly veiled hint that a sentence to
> this effect should be in the commit message.

You mean "a (clearly not thinly enough) veiled hint". :-)

I agree with Andy re both the code and the commit message.

 -George

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