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From: Dave Hansen <dave.hansen@intel.com>
To: Ingo Molnar <mingo@kernel.org>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, Borislav Petkov <bp@alien8.de>,
	Andy Lutomirski <luto@kernel.org>,
	Bhupesh Sharma <bhsharma@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 1/2] x86/efi: Unmap efi boot services code/data regions from efi_pgd
Date: Mon, 22 Oct 2018 07:12:25 -0700	[thread overview]
Message-ID: <f88841ec-e104-fa8b-0be6-7418c7bf5161@intel.com> (raw)
In-Reply-To: <20181022015738.GB24095@gmail.com>

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.
https://www.intel.com/content/www/us/en/architecture-and-technology/l1tf.html

  parent reply	other threads:[~2018-10-22 14:12 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-22  1:35 [PATCH 0/2] Unmap efi boot services code/data regions after boot Sai Praneeth Prakhya
2018-10-22  1:35 ` [PATCH 1/2] x86/efi: Unmap efi boot services code/data regions from efi_pgd Sai Praneeth Prakhya
2018-10-22  1:57   ` Ingo Molnar
2018-10-22  3:00     ` Prakhya, Sai Praneeth
2018-10-22  4:58     ` Andy Lutomirski
2018-10-22 17:35       ` Prakhya, Sai Praneeth
2018-10-22 14:12     ` Dave Hansen [this message]
2018-10-22 17:36       ` Prakhya, Sai Praneeth
2018-10-22  1:35 ` [PATCH 2/2] x86/efi: Move efi_<reserve/free>_boot_services() to arch/x86 Sai Praneeth Prakhya

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