Re: RFC: userspace exception fixups

[Jarkko Sakkinen]

On Wed, Nov 07, 2018 at 12:56:58PM -0800, Dave Hansen wrote:
> On 11/7/18 11:01 AM, Sean Christopherson wrote:
> > Going off comments in similar code related to UMIP, we'd need to figure
> > out how to handle protection keys.
> 
> There are two options:
> 1. Don't depend on the userspace mapping.  Do get_user_pages() to find
>    the instruction in the kernel direct map, and use that.
> 2. Do a WRPKRU that allows read access, do the read, then put PKRU back.
>    This is a pain because of preemption and all that jazz.
> 
> Right now, we just let the prefetch instruction detection fail if you
> mark it unreadable with pkeys.  Tough cookies, basically.  But, that's
> just the kernel being nice, but you need it for functionality, so it's
> tougher.

I would go with one because it is the stable way to do it and we are
100% sure to not conflict with pk's.

/Jarkko