linux-kernel - Re: [RFC PATCH 1/5] x86/kexec: Do unconditional WBINVD for bare-metal in stop_this

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Message-ID: <2a949eff1971c57f447ab9250eb034a009c144bd.camel@intel.com>
Date: Fri, 14 Mar 2025 18:57:06 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [RFC PATCH 1/5] x86/kexec: Do unconditional WBINVD for bare-metal
 in stop_this_cpu()

On Fri, 2025-03-14 at 13:18 -0500, Tom Lendacky wrote:
> > Does the stop_this_cpu() part never come into play for SME either? It looks
> > like
> > it was added for TDX guest kexec, but is a general ACPI thing.
> 
> It is a general ACPI thing, but I don't know of it being used by our MADT
> tables.
> 
> > 
> > Regarding the kasan thing, I was looking at this too:
> > wbinvd()
> > cpumask_clear_cpu()
> >    clear_bit()
> >      instrument_atomic_write()
> >        kasan_check_write()
> >          __kasan_check_write() <- non-inline
> 
> Yes, this does look worrisome. Too bad there isn't a way to turn off KASAN
> for a single function.

I wonder why that one has an explicit call, compared to compiler generated
stuff. It makes me wonder if there is just some KASAN skipping bit-wise
operations that could be done to fix it.

For stop_this_cpu(), not sure how to avoid it. Maybe just a raw jump to the
function pointer or something. It's not supposed to return. If it is actually
not an issue due foreseeable lack of real world HW/firmware, a comment would be
nice touch.

Ok, well based on your earlier point, the new code actually doesn't make things
worse for SME. For TDX the late function calls are not a problem. So we'll leave
it to you guys.

Thanks for responding so quickly.