linux-kernel - [19/82] x86, mtrr: Assume SYS_CFG[Tom2ForceMemTypeWB] exists on all future AMD CPUs

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Message-Id: <20101119215640.306813138@clark.site>
Date:	Fri, 19 Nov 2010 13:55:40 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Andreas Herrmann <andreas.herrmann3@....com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [19/82] x86, mtrr: Assume SYS_CFG[Tom2ForceMemTypeWB] exists on all future AMD CPUs

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Andreas Herrmann <andreas.herrmann3@....com>

commit 3fdbf004c1706480a7c7fac3c9d836fa6df20d7d upstream.

Instead of adapting the CPU family check in amd_special_default_mtrr()
for each new CPU family assume that all new AMD CPUs support the
necessary bits in SYS_CFG MSR.

Tom2Enabled is architectural (defined in APM Vol.2).
Tom2ForceMemTypeWB is defined in all BKDGs starting with K8 NPT.
In pre K8-NPT BKDG this bit is reserved (read as zero).

W/o this adaption Linux would unnecessarily complain about bad MTRR
settings on every new AMD CPU family, e.g.

[    0.000000] WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing 4863MB of RAM.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>
LKML-Reference: <20100930123235.GB20545@...e.amd.com>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/x86/kernel/cpu/mtrr/cleanup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/mtrr/cleanup.c
+++ b/arch/x86/kernel/cpu/mtrr/cleanup.c
@@ -827,7 +827,7 @@ int __init amd_special_default_mtrr(void

 	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
 		return 0;
-	if (boot_cpu_data.x86 < 0xf || boot_cpu_data.x86 > 0x11)
+	if (boot_cpu_data.x86 < 0xf)
 		return 0;
 	/* In case some hypervisor doesn't pass SYSCFG through: */
 	if (rdmsr_safe(MSR_K8_SYSCFG, &l, &h) < 0)

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