On Tue, May 05, 2020 at 11:46:48AM -0700, Tony Luck wrote:
> An interesting thing happened when a guest Linux instance took
> a machine check. The VMM unmapped the bad page from guest physical
> space and passed the machine check to the guest.
>
> Linux took all the normal actions to offline the page from the process
> that was using it. But then guest Linux crashed because it said there
> was a second machine check inside the kernel with this stack trace:
>
> do_memory_failure
> set_mce_nospec
> set_memory_uc
> _set_memory_uc
> change_page_attr_set_clr
> cpa_flush
> clflush_cache_range_opt
Maybe I don't see it but how can clflush_cache_range_opt() call
cpa_flush() ?
> This was odd, because a CLFLUSH instruction shouldn't raise a machine
> check (it isn't consuming the data). Further investigation showed that
> the VMM had passed in another machine check because is appeared that the
> guest was accessing the bad page.
This is where you lost me - if the VMM unmaps the page during the first
MCE, how can the guest even attempt to touch it and do this stack trace
above?
/me is confused.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
