Re: [RFC v3 PATCH 5/5] x86: check VM_DEAD flag in page fault

[Yang Shi]

On 7/2/18 6:37 AM, Michal Hocko wrote:
> On Mon 02-07-18 15:33:11, Laurent Dufour wrote:
> > On 02/07/2018 14:45, Michal Hocko wrote:
> > > On Mon 02-07-18 14:26:09, Laurent Dufour wrote:
> > > > On 02/07/2018 14:15, Michal Hocko wrote:
> [...]
> > > > > We already do have a model for that. Have a look at MMF_UNSTABLE.
> > > > MMF_UNSTABLE is a mm's flag, here this is a VMA's flag which is checked.
> > > Yeah, and we have the VMA ready for all places where we do check the
> > > flag. check_stable_address_space can be made to get vma rather than mm.
> > Yeah, this would have been more efficient to check that flag at the beginning
> > of the page fault handler rather than the end, but this way it will be easier
> > to handle the speculative page fault too ;)
> The thing is that it doesn't really need to be called earlier. You are
> not risking data corruption on file backed mappings.

OK, I just think it could save a few cycles to check the flag earlier.

If nobody think it is necessary, we definitely could re-use 
check_stable_address_space(), just return VM_FAULT_SIGSEGV for VM_DEAD 
vma, and check for both shared and non-shared.

Thanks,
Yang

>