lkml.org 
[lkml]   [2020]   [Jun]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace)
    Hi Peter,

    On Tue, Jun 23, 2020 at 12:45:59PM +0200, Peter Zijlstra wrote:
    > On Tue, Jun 23, 2020 at 11:45:19AM +0200, Joerg Roedel wrote:
    > > Or maybe you have a better idea how to implement this, so I'd like to
    > > hear your opinion first before I spend too many days implementing
    > > something.
    >
    > OK, excuse my ignorance, but I'm not seeing how that IST shifting
    > nonsense would've helped in the first place.
    >
    > If I understand correctly the problem is:
    >
    > <#VC>
    > shift IST
    > <NMI>
    > ... does stuff
    > <#VC> # again, safe because the shift
    >
    > But what happens if you get the NMI before your IST adjustment?

    The v3 patchset implements an unconditional shift of the #VC IST entry
    in the NMI handler, before it can trigger a #VC exception.

    > Either way around we get to fix this up in NMI (and any other IST
    > exception that can happen while in #VC, hello #MC). And more complexity
    > there is the very last thing we need :-(

    Yes, in whatever way this gets implemented, it needs some fixup in the
    NMI handler. But that can happen in C code, so it does not make the
    assembly more complex, at least.

    > There's no way you can fix up the IDT without getting an NMI first.

    Not sure what you mean by this.

    > This entire exception model is fundamentally buggered :-/

    Regards,

    Joerg

    \
     
     \ /
      Last update: 2020-06-23 13:11    [W:2.390 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site