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

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