linux-kernel - Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine

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Date:	Tue, 02 Oct 2012 14:50:09 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	T Makphaibulchoke <tmac@...com>
CC:	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	akpm@...ux-foundation.org, yinghai@...nel.org, tiwai@...e.de,
	viro@...iv.linux.org.uk, aarcange@...hat.com, tony.luck@...el.com,
	mgorman@...e.de, weiyang@...ux.vnet.ibm.com,
	octavian.purdila@...el.com, paul.gortmaker@...driver.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi
 machine

On 10/02/2012 02:32 PM, T Makphaibulchoke wrote:
> Changing devmem_is_allowed so that on an EFI machine, access to physical
> address below 1 MB is allowed only to physical pages that are valid in
> the EFI memory map.  This prevents the possibility of an MCE due to
> accessing an invalid physical address.

What?

That sounds like exactly the opposite of normal /dev/mem behavior... we
allow access to non-memory resources (which really could do anything if
misused), but not memory.

You seem like you're flipping it on its head.

	-hpa

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