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Date: Wed, 24 Feb 2016 17:20:02 +0100
From: Borislav Petkov <bp@alien8.de>
To: Matt Fleming <matt@codeblueprint.co.uk>,
        Andy Lutomirski <luto@amacapital.net>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Toshi Kani <toshi.kani@hp.com>, Brian Gerst <brgerst@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Luis Rodriguez <mcgrof@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Denys Vlasenko <dvlasenk@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, ricardo.neri@intel.com,
        Hugh Dickins <hughd@google.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page
 table mappings
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On Wed, Feb 24, 2016 at 02:10:46PM +0000, Matt Fleming wrote:
> > Normally, the only pages with are _PAGE_GLOBAL are those that are in
> > the normal kernel mappings (swapper_pg_dir and normal mm_struct pgds).
> > By allowing _PAGE_GLOBAL to be set in EFI mappings, you're breaking
> > that convention, which forces you to use extra-expensive
> > __flush_tlb_all calls in efi_call_virt.

Hold on, do you mean the __flush_tlb_all() in the CONFIG_EFI_MIXED code?

That's mixed mode. I think you mean the FLUSH_TLB_ALL in efi_call.
That's EFI on 64-bit but that is mandated by the spec, AFAIR.

So the EFI runtime crap should not change once it is mapped. And those
should be global. It is only natural.

> Nope. The "if (cpa->pgd)" guard ensures that we only call that
> function for the EFI mapping code - no one else sets ->pgd.

But it could - there's no guarantee. kernel_map_pages_in_pgd() is an
exported facility.

-- 
Regards/Gruss,
    Boris.

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