Re: 32 bit qemu regression from v6.5 tip pull [6c480f222128 x86/alternative: Rewrite optimize_nops() some]
From: Peter Zijlstra
Date: Mon Oct 30 2023 - 07:45:10 EST
On Mon, Oct 30, 2023 at 10:55:26AM +0000, Richard Purdie wrote:
> On Mon, 2023-10-30 at 09:26 +0100, Peter Zijlstra wrote:
> > On Sun, Oct 29, 2023 at 02:41:46PM -0400, Paul Gortmaker wrote:
> > > The TL;DR is that the Yocto folks encountered a regression in their
> > > automated QA tests (after a move from v6.4 --> v6.5) where non-KVM
> > > enabled boot tests on 32 bit x86 would (with ~2% frequency) splat with:
> >
> > You're sure you're not running into this here:
> >
> > https://lkml.kernel.org/r/20230706170537.95959-1-richard.henderson@xxxxxxxxxx
> >
> > ?
>
> We're using qemu 8.1.0. Whilst I will get us updated to 8.1.2 and see
> if that helps, I think those commits are in 8.1.0:
>
> $ git show cb62bd15e14e304617d250158b77d0deb032f03
> commit cb62bd15e14e304617d250158b77d0deb032f032
> Author: Richard Henderson <richard.henderson@xxxxxxxxxx>
> Date: Thu Jul 6 08:45:13 2023 +0100
>
> accel/tcg: Split out cpu_exec_longjmp_cleanup
> [...]
> $ git tag --contains cb62bd15e14e304617d250158b77d0deb032f03
> v8.1.0
> v8.1.0-rc0
> v8.1.0-rc1
> v8.1.0-rc2
> v8.1.0-rc3
> v8.1.0-rc4
> v8.1.1
> v8.1.2
>
> Similarly for:
>
> commit deba78709ae8ce103e2248413857747f804cd1ef
> Author: Richard Henderson <richard.henderson@xxxxxxxxxx>
> Date: Thu Jul 6 17:55:48 2023 +0100
>
> accel/tcg: Always lock pages before translation
>
> and
>
> commit ad17868eb162a5466d8ad43e5ccb428776403308
> Author: Richard Henderson <richard.henderson@xxxxxxxxxx>
> Date: Wed Jul 26 12:58:08 2023 -0700
>
> accel/tcg: Clear tcg_ctx->gen_tb on buffer overflow
> [...]
> Fixes: deba78709ae8 ("accel/tcg: Always lock pages before translation")
>
> Both of which are also in 8.1.0.
>
> Is there any other patch related to those we might be missing?
Not sure -- afaik that was it.
Thomas was looking at this and wondered if something like the below
would help?
---
arch/x86/kernel/alternative.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 73be3931e4f0..fd44739828f7 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1685,8 +1685,8 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
} else {
local_irq_save(flags);
memcpy(addr, opcode, len);
- local_irq_restore(flags);
sync_core();
+ local_irq_restore(flags);
/*
* Could also do a CLFLUSH here to speed up CPU recovery; but