linux-kernel - Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings

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Message-ID: <20160224162002.GE3888@pd.tnic>
Date:	Wed, 24 Feb 2016 17:20:02 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Matt Fleming <matt@...eblueprint.co.uk>,
	Andy Lutomirski <luto@...capital.net>
Cc:	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
	Toshi Kani <toshi.kani@...com>,
	Brian Gerst <brgerst@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Luis Rodriguez <mcgrof@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>, ricardo.neri@...el.com,
	Hugh Dickins <hughd@...gle.com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page
 table mappings

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.

ECO tip #101: Trim your mails when you reply.