Messages in this thread | | | Date | Fri, 10 Dec 2021 15:18:33 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v1 04/12] x86/mce: Remove noinstr annotation from mce_setup() |
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On Thu, Dec 09, 2021 at 01:16:56PM +0100, Peter Zijlstra wrote: > Yeah, that's what it does; but *why* is that correct?
Correct, shmorect - it is the #MC handler nasty.
> I'm thinking we're well past the exception entry code and are only > using noinstr as a means to limit the amount of code in the MCE > handler?
Well, one of the calls to mce_gather_info() happen in #MC context. That one calls mce_setup() and that thing calls out to
# ./arch/x86/include/asm/paravirt.h:116: PVOP_VCALL4(cpu.cpuid, eax, ebx, ecx, edx); cmpq $0, pv_ops+176(%rip) #, pv_ops.cpu.cpuid
and you get this:
vmlinux.o: warning: objtool: pv_ops[22]: xen_cpuid vmlinux.o: warning: objtool: pv_ops[22]: native_cpuid vmlinux.o: warning: objtool: mce_setup()+0xa0: call to pv_ops[22]() leaves .noinstr.text section
I think this is too much and too specific text to stick in the code as a comment.
I can stick it in the commit message if you prefer that but frankly, seeing those instrumentation_begin/_end() sandwiches are already hints enough in my head to read "TODO" there...
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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