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Date:   Thu, 30 Aug 2018 18:48:50 -0700
From:   Tony Luck <>
To:     Linus Torvalds <>
Cc:     Thomas Gleixner <>,
        Ingo Molnar <>,
        "H. Peter Anvin" <>, Borislav Petkov <>,
        Linux Edac Mailing List <>,
        Linux Kernel Mailing List <>,
        X86-ML <>, Dan Williams <>,
Subject: Re: [PATCH] x86/mce: Fix set_mce_nospec() to avoid #GP fault

On Thu, Aug 30, 2018 at 6:30 PM Linus Torvalds
<> wrote:
> On Thu, Aug 30, 2018 at 2:45 PM Tony Luck <> wrote:
> >
> > Fix is to move one step at a time. First mark the page not present
> > (using the decoy address). Then it is safe to use the actual address
> > of the 1:1 mapping to mark it "uc", and finally as present.
> Can't we do it in one step, but make sure that he clflush gets the real address?

I'd like to, but I'd need to have a way to mark the address as needing fixing as
it gets passed from set_memory_uc() to _set_memory_uc() to
to change_page_attr_set_clear()

Just checking "do we have a non-canonical address" at the bottom of that
call stack and flipping bit 63 back on again seems like a bad idea. But adding
extra flag arguments is majorly ugly too.


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