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From: Borislav Petkov <bp@alien8.de>
To: Tony Luck <tony.luck@intel.com>
Cc: Jue Wang <juew@google.com>,
	Dan Williams <dan.j.williams@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/mm: Don't try to change poison pages to uncacheable in a guest
Date: Sat, 16 May 2020 08:54:31 +0200	[thread overview]
Message-ID: <20200516065431.GB25771@zn.tnic> (raw)
In-Reply-To: <20200505184648.2264-1-tony.luck@intel.com>

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

  reply	other threads:[~2020-05-16  6:54 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-05 18:46 [PATCH] x86/mm: Don't try to change poison pages to uncacheable in a guest Tony Luck
2020-05-16  6:54 ` Borislav Petkov [this message]
2020-05-16 14:47   ` Luck, Tony
2020-05-16 15:02     ` Borislav Petkov
2020-05-17  1:52       ` Luck, Tony
     [not found]         ` <CAPcxDJ50pbuTbittyvPwKq1uUT8q8jJ+dHH8rCug8a1DDZXVYw@mail.gmail.com>
     [not found]           ` <CAPcxDJ6f3pBpwiR9nvXN_g_HBa1RAMG+aOmgfXLFT6aZ9HQn3w@mail.gmail.com>
2020-05-18 13:48             ` Borislav Petkov
2020-05-18 15:36               ` Luck, Tony
2020-05-18 16:55                 ` Borislav Petkov
2020-05-18 18:26                   ` Luck, Tony
2020-05-18 19:20                     ` Dan Williams
2020-05-19  5:22                     ` Sean Christopherson
2020-05-19  8:50                     ` Borislav Petkov
2020-05-20 16:35                       ` [PATCH v2] x86/mm: Change so poison pages are either unmapped or marked uncacheable Luck, Tony
2020-05-25 11:00                         ` [tip: ras/core] x86/{mce,mm}: " tip-bot2 for Tony Luck
2020-05-25 20:40                           ` Borislav Petkov
2020-05-26 17:37                             ` Luck, Tony
     [not found]                               ` <CAPcxDJ5arJojbY4pzOvYh=waSPd3X_JJb1_PSuzd+jQ0qbvFsA@mail.gmail.com>
     [not found]                                 ` <CAPcxDJ54EgX-SaDV=Lm+a2-43O68LhomyYfYdCDz38HGJCkh7g@mail.gmail.com>
2020-05-26 19:46                                   ` Borislav Petkov
2020-05-26 19:56                         ` [tip: ras/core] x86/{mce,mm}: Unmap the entire page if the whole page is affected and poisoned tip-bot2 for Tony Luck
2020-05-19  5:04                   ` [PATCH] x86/mm: Don't try to change poison pages to uncacheable in a guest Sean Christopherson

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