linux-kernel - Re: [PATCH] x86_64/efi: Mapping Boot and Runtime EFI memory regions to different starting virtual address

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Message-ID: <55B9D806.7030705@zytor.com>
Date:	Thu, 30 Jul 2015 00:53:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>,
	Matt Fleming <matt@...eblueprint.co.uk>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org, "Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [PATCH] x86_64/efi: Mapping Boot and Runtime EFI memory regions
 to different starting virtual address

On 07/29/2015 09:32 PM, Lee, Chun-Yi wrote:
> When testing hibernate, I found the EFI runtime services was broken
> on some old EFI machines on my hand, Intel DQ57TM development board
> and Acer Gateway Z5WT2 notebook.
> 
> After printing the EFI memmap and virtual address mapping on -4G area,
> found those issue machines keep the physical address of Runtime
> Data/Code regions unchanged but not Boot Data/Code. The logs were
> attached on openSUSE bug:
>     https://bugzilla.suse.com/show_bug.cgi?id=939979
> 
> Due to Boot Data/Code can be used by OS as available memory regions,
> so those old EFI BIOS do not keep the physical address of Boot regions
> unchanged. But, address of Runtime regions are the same.
> 
> On Intel DQ57TM, sometimes the order of EFI Boot regions changed. On
> Acer Gateway Z5WT2, the amount of EFI Boot regions changed.
> 
> The above changing of EFI Boot regions causes the EFI Runtime Data/Code
> may not mapping to constant virtual address, that's because the EFI Boot
> and Runtime regions are interleaved and EFI va mapping applied PMD
> 2M-aligned logic.
> 
> A workaround of this situation is mapping Boot and Runtime regions to
> different starting virtual address. Then the changing of Boot Data/Code
> regions will not affect to the virtual address mapping to Runtime
> Data/Code.
> 
> This patch adds codes for mapping Boot Data/Code regions start from
> 0xffff_ffff_0000_0000, has 1G space. And mapping Runtime Data/Code
> regions start from 0xffff_fffe_c000_0000 that has 63G space.
> 

This changelog is at least partially incomprehensive.  It also seems
more than a bit aggressive to expect that 1 GB will be sufficient forever.

	-hpa


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