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Re: [Qemu-devel] [6449] MTRR support on x86 (Carl-Daniel Hailfinger)
From: |
Carl-Daniel Hailfinger |
Subject: |
Re: [Qemu-devel] [6449] MTRR support on x86 (Carl-Daniel Hailfinger) |
Date: |
Mon, 26 Jan 2009 22:32:40 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.17) Gecko/20080922 SUSE/1.1.12-0.1 SeaMonkey/1.1.12 |
Hi,
thanks for committing this patch. It seems the chunk in
target-i386/machine.c got lost and save/restore functionality is missing.
Should I resend that part?
Regards,
Carl-Daniel
On 26.01.2009 18:53, Anthony Liguori wrote:
> Revision: 6449
> http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=6449
> Author: aliguori
> Date: 2009-01-26 17:53:04 +0000 (Mon, 26 Jan 2009)
>
> Log Message:
> -----------
> MTRR support on x86 (Carl-Daniel Hailfinger)
>
> The current codebase ignores MTRR (Memory Type Range Register)
> configuration writes and reads because Qemu does not implement caching.
> All BIOS/firmware in know of for x86 do implement a mode called
> Cache-as-RAM (CAR) which locks down the CPU cache lines and uses the CPU
> cache like RAM before RAM is enabled. Qemu assumes RAM is accessible
> from the start, but it would be nice to be able to run real
> BIOS/firmware in Qemu. For that, we need CAR support and for CAR support
> we have to support MTRRs.
>
> This patch is a first step in that direction. MTRRs are MSRs supported
> by all recent x86 CPUs, even old i586. Besides influencing cache, the
> MTRRs can be written and read back, so discarding MTRR writes violates
> the expectations of existing code out there.
>
> An added benefit of this patch is that it fixes the following Linux
> kernel error message present in recent kernels (provided the BIOS has
> the recent MTRR patches applied):
> ------------[ cut here ]------------
> WARNING: at arch/x86/kernel/cpu/mtrr/main.c:1500
> mtrr_trim_uncached_memory+0x382/0x384()
> WARNING: strange, CPU MTRRs all blank?
> Modules linked in:
> Supported: Yes
> Pid: 0, comm: swapper Not tainted 2.6.27.7-9-default #1
> [<c0106570>] dump_trace+0x6b/0x249
> [<c01070a5>] show_trace+0x20/0x39
> [<c0343c02>] dump_stack+0x71/0x76
> [<c012acb2>] warn_slowpath+0x6f/0x90
> [<c0542f8f>] mtrr_trim_uncached_memory+0x382/0x384
> [<c053f24d>] setup_arch+0x40d/0x639
> [<c053a6ac>] start_kernel+0x6b/0x31f
> =======================
> ---[ end trace 4eaa2a86a8e2da22 ]---
>
> Handle common x86 MTRR reads and writes, but don't act on them.
>
> Signed-off-by: Carl-Daniel Hailfinger <address@hidden>
> Signed-off-by: Anthony Liguori <address@hidden>
>
> Modified Paths:
> --------------
> trunk/target-i386/cpu.h
> trunk/target-i386/op_helper.c
>
--
http://www.hailfinger.org/