On Mon 15-08-16 02:06:31, Michael S. Tsirkin wrote:
[...]
> So fundamentally, won't the following make copy to/from user
> return EFAULT? If yes, vhost is already prepared to handle that.
>
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index dc80230..e5dbee5 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1309,6 +1309,11 @@ retry:
> might_sleep();
> }
>
> + if (unlikely(test_bit(MMF_UNSTABLE, &mm->flags))) {
> + bad_area(regs, error_code, address);
> + return;
> + }
> +
> vma = find_vma(mm, address);
> if (unlikely(!vma)) {
> bad_area(regs, error_code, address);
This would be racy but even if we did the check _after_ the #PF is
handled then I am not very happy to touch the #PF path which is quite
hot for something as rare as OOM and which only has one user which needs
a special handling. That is the primary reason why I prefer the specific
API.
--
Michal Hocko
SUSE Labs
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