Re: [PATCH v3 1/5] x86/kexec: do unconditional WBINVD for bare-metal in stop_this_cpu()

[Huang, Kai]

On 11/04/2024 2:12 am, Kirill A. Shutemov wrote:
> On Mon, Apr 08, 2024 at 12:44:54AM +1200, Kai Huang wrote:
> > TL;DR:
>
> The commit message is waaay too verbose for no good reason. You don't
> really need to repeat all the history around this code.

Could you be more specific?

I was following Boris's suggestion to summerize all the discussion 
around the "unconditional WBINVD" issue.

https://lore.kernel.org/linux-kernel/20240228110207.GCZd8Sr8mXHA2KTiLz@fat_crate.local/

I can try to improve if I can know specifically what should be trimmed down.

> > ---
> >   arch/x86/kernel/process.c | 18 ++++++++----------
> >   1 file changed, 8 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> > index b8441147eb5e..5ba8a9c1e47a 100644
> > --- a/arch/x86/kernel/process.c
> > +++ b/arch/x86/kernel/process.c
> > @@ -813,18 +813,16 @@ void __noreturn stop_this_cpu(void *dummy)
> >   	mcheck_cpu_clear(c);
> >   
> >   	/*
> > -	 * Use wbinvd on processors that support SME. This provides support
> > -	 * for performing a successful kexec when going from SME inactive
> > -	 * to SME active (or vice-versa). The cache must be cleared so that
> > -	 * if there are entries with the same physical address, both with and
> > -	 * without the encryption bit, they don't race each other when flushed
> > -	 * and potentially end up with the wrong entry being committed to
> > -	 * memory.
> > +	 * The kernel could leave caches in incoherent state on SME/TDX
> > +	 * capable platforms.  Flush cache to avoid silent memory
> > +	 * corruption for these platforms.
> >   	 *
> > -	 * Test the CPUID bit directly because the machine might've cleared
> > -	 * X86_FEATURE_SME due to cmdline options.
> > +	 * stop_this_cpu() is not a fast path, just do unconditional
> > +	 * WBINVD for simplicity.  But only do WBINVD for bare-metal
> > +	 * as TDX guests and SEV-ES/SEV-SNP guests will get unexpected
> > +	 * (and unnecessary) #VE and may unable to handle.
>
> s/#VE/exception/
>
> On SEV it is #VC, not #VE.

Thanks.  I think I'll use "exception (#VE or #VC)" which is clearer, as 
Tom typed in the comments to patch 2.