linux-kernel - Re: [Xen-devel] [PATCH 7 of 7] x86: always explicitly map acpi memory

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Message-ID: <86802c440809071635l1457659bufeefa6e65cc34bdf@mail.gmail.com>
Date:	Sun, 7 Sep 2008 16:35:25 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Xen Devel" <xen-devel@...ts.xensource.com>,
	"Andi Kleen" <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] [PATCH 7 of 7] x86: always explicitly map acpi memory

On Sun, Sep 7, 2008 at 3:21 PM, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> Always map acpi tables, rather than assuming we can use the normal
> linear mapping to access the acpi tables.  This is necessary in a
> virtual environment where the linear mappings are to pseudo-physical
> memory, but the acpi tables exist at a real physical address.  It
> doesn't hurt to map in the normal non-virtual case, so just do it
> unconditionally.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> ---
>  arch/x86/kernel/acpi/boot.c |    3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -126,9 +126,6 @@
>
>        if (!phys || !size)
>                return NULL;
> -
> -       if (phys+size <= (max_low_pfn_mapped << PAGE_SHIFT))
> -               return __va(phys);
>
>        if (prev_map)
>                early_iounmap(prev_map, prev_size);
>

actually,
case 1: acpi tables near mmio, range, we don't map them from
2.6.27-rc1, and it is bigger than max_low_mapped...
case 2: some strange system put acpi in the middle of RAM... like when
8G ram installed, but MMIO is 3.5G, BIOS put acpi tables around 2G..

YH
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