lkml.org 
[lkml]   [2020]   [Apr]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] Allow RDTSC and RDTSCP from userspace
On Sat, Apr 25, 2020 at 1:23 PM Joerg Roedel <joro@8bytes.org> wrote:
>
> On Sat, Apr 25, 2020 at 12:47:31PM -0700, Andy Lutomirski wrote:
> > I assume the race you mean is:
> >
> > #VC
> > Immediate NMI before IST gets shifted
> > #VC
> >
> > Kaboom.
> >
> > How are you dealing with this? Ultimately, I think that NMI will need
> > to turn off IST before engaging in any funny business. Let me ponder
> > this a bit.
>
> Right, I dealt with that by unconditionally shifting/unshifting the #VC IST entry
> in do_nmi() (thanks to Davin Kaplan for the idea). It might cause
> one of the IST stacks to be unused during nesting, but that is fine. The
> stack memory for #VC is only allocated when SEV-ES is active (in an
> SEV-ES VM).

Blech. It probably works, but still, yuck. It's a bit sad that we
seem to be growing more and more poorly designed happens-anywhere
exception types at an alarming rate. We seem to have #NM, #MC, #VC,
#HV, and #DB. This doesn't really scale.

--Andy

\
 
 \ /
  Last update: 2020-04-26 00:11    [W:0.188 / U:0.976 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site