Re: [PATCH v6 00/12] SVM cleanup and INVPCID feature support

[Jim Mattson]

On Thu, Mar 11, 2021 at 12:32 PM Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Thu, Mar 11, 2021 at 09:07:55PM +0100, Borislav Petkov wrote:
> > On Wed, Mar 10, 2021 at 07:21:23PM -0600, Babu Moger wrote:
> > > # git bisect good
> > > 59094faf3f618b2d2b2a45acb916437d611cede6 is the first bad commit
> > > commit 59094faf3f618b2d2b2a45acb916437d611cede6
> > > Author: Borislav Petkov <bp@xxxxxxx>
> > > Date:   Mon Dec 25 13:57:16 2017 +0100
> > >
> > >     x86/kaiser: Move feature detection up
> >
> > What is the reproducer?
> >
> > Boot latest 4.9 stable kernel in a SEV guest? Can you send guest
> > .config?
> >
> > Upthread is talking about PCID, so I'm guessing host needs to be Zen3
> > with PCID. Anything else?
>
> That oops points to:
>
> [    1.237515] kernel BUG at /build/linux-dqnRSc/linux-4.9.228/arch/x86/kernel/alternative.c:709!
>
> which is:
>
>         local_flush_tlb();
>         sync_core();
>         /* Could also do a CLFLUSH here to speed up CPU recovery; but
>            that causes hangs on some VIA CPUs. */
>         for (i = 0; i < len; i++)
>                 BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);       <---
>         local_irq_restore(flags);
>         return addr;
>
> in text_poke() which basically says that the patching verification
> fails. And you have a local_flush_tlb() before that. And with PCID maybe
> it is not flushing properly or whatnot.
>
> And deep down in the TLB flushing code, it does:
>
>         if (kaiser_enabled)
>                 kaiser_flush_tlb_on_return_to_user();
>
> and that uses PCID...

I would expect kaiser_enabled to be false (and PCIDs not to be used),
since AMD CPUs are not vulnerable to Meltdown.