Messages in this thread | | | Date | Thu, 11 Apr 2024 09:54:13 +1200 | Subject | Re: [PATCH v3 1/5] x86/kexec: do unconditional WBINVD for bare-metal in stop_this_cpu() | From | "Huang, Kai" <> |
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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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