linux-kernel - Re: [PATCH] phys_efi_set_virtual_address

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Message-ID: <4FE3BDD9.60105@zytor.com>
Date:	Thu, 21 Jun 2012 17:35:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Robin Holt <holt@....com>
CC:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-kernel@...r.kernel.org,
	"Sakkinen, Jarkko" <jarkko.sakkinen@...el.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH] phys_efi_set_virtual_address_map needs va, no pa.

On 06/21/2012 09:52 AM, Robin Holt wrote:
> 
> I am completely lost as to what should be done.  How do we know
> which identity maps need to be created?  Do we just add them as we are
> scanning the e820/EFI memory maps and include the reserved, etc ranges?
> Do we look at the table handed to us by EFI at the beginning of boot and
> use that as the basis?  Or do we simply wait until the kernel's memory
> initialization is complete and cover all of physical memory from zero
> up to the highest physical address?
> 

Robin, we already create the 1:1 maps.  Right now there is some
weirdness with some of the issues that you mention, but that is
orthogonal to this.

The 1:1 map created for the kernel is created at a specific offset,
__PAGE_OFFSET, and is propagated into every vm context created by the
kernel.  There are two problems:

1. The "initial" (32 bit) or "trampoline" (64 bit) maps aren't on the
list of vm contexts created by the kernel (pgd_list), so they never get
updated after a particular point in the boot.

2. The initial/trampoline maps need these mappings not just at address
__PAGE_OFFSET, but also at address zero (identity mapping), which means
that just adding it to the pgd_list is insufficient.

Note that i386-PAE is unaffected, simply because the contents of the top
(3rd) level is always fixed.

	-hpa

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