Re: [PATCH 1/4] x86/coco: Add a new CC attribute to unify cache flush during kexec

[Dave Young]

On Wed, 21 Feb 2024 at 17:33, Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Tue, Feb 20, 2024 at 04:30:13PM -0600, Tom Lendacky wrote:
> > I believe the issues were that different Intel systems would hang or reset
> > and it was bisected to that commit that added the WBINVD. It was a while
> > ago, but I remember that they were similar to what the 1f5e7eb7868e commit
> > ended up fixing, which was debugged because sometimes the WBINVD was still
> > occasionally issued resulting in the following patch
> >
> >   9b040453d444 ("x86/smp: Dont access non-existing CPUID leaf")
> >
> > It just means that if we go to an unconditional WBINVD, then we need to be
> > careful.
>
> Let's try it.
>
> Dave, do you remember what issues
>
>   f23d74f6c66c ("x86/mm: Rework wbinvd, hlt operation in stop_this_cpu()")
>
> fixed?

It should be a kexec reboot failure describe in below thread:
https://lore.kernel.org/lkml/20180117072123.GA1866@xxxxxxxxxxxxxxxxxxxxxxxxxx/

>
> If so, can you try the below diff ontop of latest tip/master to see if
> those issues would reappear?

It was reproduced on an old laptop (Thinkpad t440s or t480s, I can not
remember), but I have replaced them with a new different one.  I tried
the latest tip-master with the if condition commented out, kexec
reboot works fine.

Let me try to find an old laptop to see if I can do more tests, will
get back later next week.

>
> Thx.
>
> ---
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index ab49ade31b0d..ec4dcc9f70ca 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -824,8 +824,7 @@ void __noreturn stop_this_cpu(void *dummy)
>          * Test the CPUID bit directly because the machine might've cleared
>          * X86_FEATURE_SME due to cmdline options.
>          */
> -       if (c->extended_cpuid_level >= 0x8000001f && (cpuid_eax(0x8000001f) & BIT(0)))
> -               native_wbinvd();
> +       native_wbinvd();
>
>         /*
>          * This brings a cache line back and dirties it, but
>
> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
>