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

Borislav Petkov
2021-03-11T20:32:57Z

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@suse.de>
> > 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...

Anyway, needs more info.

--
Regards/Gruss,
Boris.