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Date:   Mon, 22 Oct 2018 17:36:48 +0000
From:   "Prakhya, Sai Praneeth" <>
To:     "Hansen, Dave" <>,
        Ingo Molnar <>
CC:     "" <>,
        "" <>,
        "" <>, Borislav Petkov <>,
        "Andy Lutomirski" <>,
        Bhupesh Sharma <>,
        "Thomas Gleixner" <>,
        Peter Zijlstra <>,
        "Ard Biesheuvel" <>,
        Peter Zijlstra <>
Subject: RE: [PATCH 1/2] x86/efi: Unmap efi boot services code/data regions
 from efi_pgd

> On 10/21/2018 06:57 PM, Ingo Molnar wrote:
> > Does the CPU _ever_ look look at the PFN if the page is
> > !_PAGE_PRESENT, for example speculatively? If yes then what is the
> > recommended value for the pfn - zero perhaps?
> I'll never say never. :)
> For L1TF[1], we know the CPU did exactly this; it ignored the _PAGE_PRESENT
> bit when fetching data from the L1.  That's what is worked around with the gunk
> in arch/x86/include/asm/pgtable-invert.h.
> I think Andi plugged the code in here at a low enough level in the page table
> manipulation that pageattr.c should inherit it without doing anything explicit.
> But, Sai, you might want to double-check this.
> 1.
> technology/l1tf.html

Sure! Dave. Thanks for the link. I will take a look at it.


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