x86, mtrr: Assume SYS_CFG[Tom2ForceMemTypeWB] exists on all future AMD CPUs

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.

Cc: stable@kernel.org # .32.x, .35.x
Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
LKML-Reference: <20100930123235.GB20545@loge.amd.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c b/arch/x86/kernel/cpu/mtrr/cleanup.c
index c5f59d07142562e9c673572970ae79fca1e3622e..ac140c7be396b6f55c97521ddcd572df664e95b6 100644 (file)
--- 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)