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

[Kefeng Wang]

On 2023/5/26 1:18, Dave Hansen wrote:
> On 5/7/23 19:22, Kefeng Wang wrote:
> > Both EX_TYPE_FAULT_MCE_SAFE and EX_TYPE_DEFAULT_MCE_SAFE exception
> > fixup types are used to identify fixups which allow in kernel #MC
> > recovery, that is the Machine Check Safe Copy.
> >
> > For now, the MCE_IN_KERNEL_COPYIN flag is only set for EX_TYPE_COPY
> > and EX_TYPE_UACCESS when copy from user, and corrupted page is
> > isolated in this case, for MC-safe copy, memory_failure() is not
> > always called, some places, like __wp_page_copy_user, copy_subpage,
> > copy_user_gigantic_page and ksm_might_need_to_copy manually call
> > memory_failure_queue() to cope with such unhandled error pages,
> > recently coredump hwposion recovery support[1] is asked to do the
> > same thing, and there are some other already existed MC-safe copy
> > scenarios, eg, nvdimm, dm-writecache, dax, which has similar issue.
>
> That has to set some kind of record for run-on sentences.  Could you
> please try to rewrite this coherently?
>
> > The best way to fix them is set MCE_IN_KERNEL_COPYIN to MCE_SAFE
> > exception, then kill_me_never() will be queued to call memory_failure()
> > in do_machine_check() to isolate corrupted page, which avoid calling
> > memory_failure_queue() after every MC-safe copy return.
>
> Could you try to send a v2 of this with a clear problem statement?

:( will try to make it more clear.

> What is the end user visible effect of the problem and of your solution?

The corrupted page won't be isolated for MC-safe copy scenario, and it 
could be accessed again by use application.