Re: [PATCH v2] x86/mce: set MCE_IN_KERNEL_COPYIN for all MC-Safe Copy

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On 2023/5/26 15:09, Borislav Petkov wrote:
On Fri, May 26, 2023 at 02:32:42PM +0800, Kefeng Wang wrote:
The best way to fix them is set MCE_IN_KERNEL_COPYIN for MC-Safe Copy,
then let the core do_machine_check() to isolate corrupted page instead
of doing it one-by-one.

No, this whole thing is confused.

  * Indicates an MCE that happened in kernel space while copying data
  * from user.

#define MCE_IN_KERNEL_COPYIN

This is a very specific exception type: EX_TYPE_COPY which got added by

   278b917f8cb9 ("x86/mce: Add _ASM_EXTABLE_CPY for copy user access")

but Linus then removed all such user copy exception points in

   034ff37d3407 ("x86: rewrite '__copy_user_nocache' function")

So now that EX_TYPE_COPY never happens.

Is this broken the recover when kernel was copying from user space?

+ Youquan  could you help to check it?


And what you're doing is lumping the handling for
EX_TYPE_DEFAULT_MCE_SAFE and EX_TYPE_FAULT_MCE_SAFE together and saying
that the MCE happened while copying data from user.

And XSTATE_OP() is one example where this is not really the case.


Oh, for XSTATE_OP(), it uses EX_TYPE_DEFAULT_MCE_SAFE, but I'm focus on EX_TYPE_DEFAULT_MCE_SAFE, which use copy_mc (arch/x86/lib/copy_mc_64.S), like I maintained in changelog, CoW/Coredump/nvdimm/dax, they use copy_mc_xxx function, sorry for mixed them up.


So no, this is not correct.

so only add MCE_IN_KERNEL_COPYIN for EX_TYPE_DEFAULT_MCE_SAFE?

diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
index c4477162c07d..6d2587994623 100644
--- a/arch/x86/kernel/cpu/mce/severity.c
+++ b/arch/x86/kernel/cpu/mce/severity.c
@@ -293,11 +293,11 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)
        case EX_TYPE_COPY:
                if (!copy_user)
                        return IN_KERNEL;
+               fallthrough;
+       case EX_TYPE_DEFAULT_MCE_SAFE:
                m->kflags |= MCE_IN_KERNEL_COPYIN;
                fallthrough;
-
        case EX_TYPE_FAULT_MCE_SAFE:
-       case EX_TYPE_DEFAULT_MCE_SAFE:
                m->kflags |= MCE_IN_KERNEL_RECOV;
                return IN_KERNEL_RECOV;

Correct me if I am wrong, thanks for you reviewing.







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