Re: [PATCH] x86: fix {pmd,pud}_{set,clear}_flags()

[Jan Beulich]

>>> On 19.02.18 at 17:23, <jgross@xxxxxxxx> wrote:
> On 19/02/18 15:48, Jan Beulich wrote:
>> Just like pte_{set,clear}_flags() their PMD and PUD counterparts should
>> not do any address translation. This was outright wrong under Xen
>> (causing a dead boot with no useful output on "suitable" systems), and
>> produced needlessly more complicated code (even if just slightly) when
>> paravirt was enabled.
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx 
> 
> While the changes look alright I'm really curious which kind of failure
> you are seeing, especially considering how long those functions haven't
> been changed (since more than 6 years).

It's the new use of pmd_set_flags() in 2cc42bac1c ("x86-64/Xen:
eliminate W+X mappings"), and due to the (very odd afaic) identity
map handling the issue is invisible on most systems/setups.

Jan