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Subject[PATCH] [6/7] Split large page mapping for AMD TSEG

On AMD SMM protected memory is part of the address map, but handled
internally like an MTRR. That leads to large pages getting split
internally which has some performance implications. Check for the
AMD TSEG MSR and split the large page mapping on that area
explicitely if it is part of the direct mapping.

There is also SMM ASEG, but it is in the first 1MB and already covered by
the earlier split first page patch.

Idea for this came from an earlier patch by Andreas Herrmann

On a RevF dual Socket Opteron system kernbench shows a clear
improvement from this:
(together with the earlier patches in this series, especially the
split first 2MB patch)

[lower is better]
no split stddev split stddev delta
Elapsed Time 87.146 (0.727516) 84.296 (1.09098) -3.2%
User Time 274.537 (4.05226) 273.692 (3.34344) -0.3%
System Time 34.907 (0.42492) 34.508 (0.26832) -1.1%
Percent CPU 322.5 (38.3007) 326.5 (44.5128) +1.2%

=> About 3.2% improvement in elapsed time for kernbench.

With GB pages on AMD Fam1h the impact of splitting is much higher of course,
since it would split two full GB pages (together with the first
1MB split patch) instead of two 2MB pages. I could not benchmark
a clear difference in kernbench on gbpages, so I kept it disabled
for that case

That was only limited benchmarking of course, so if someone
was interested in running more tests for the gbpages case
that could be revisited (contributions welcome)

I didn't bother implementing this for 32bit because it is very
unlikely the 32bit lowmem mapping overlaps into the TSEG near 4GB
and the 2MB low split is already handled for both.

Signed-off-by: Andi Kleen <>

arch/x86/kernel/setup_64.c | 13 +++++++++++++
include/asm-x86/msr-index.h | 1 +
2 files changed, 14 insertions(+)

Index: linux/arch/x86/kernel/setup_64.c
--- linux.orig/arch/x86/kernel/setup_64.c
+++ linux/arch/x86/kernel/setup_64.c
@@ -721,6 +721,20 @@ static void __cpuinit init_amd(struct cp

if (amd_apic_timer_broken())
disable_apic_timer = 1;
+ if (!direct_gbpages &&
+ c == &boot_cpu_data && c->x86 >= 0xf && c->x86 <= 0x11) {
+ unsigned long tseg;
+ /*
+ * Split up direct mapping around the TSEG SMM area.
+ * Don't do it for gbpages because there seems very little
+ * benefit in doing so.
+ */
+ if (!rdmsrl_safe(MSR_K8_TSEG_ADDR, &tseg) &&
+ (tseg >> PMD_SHIFT) < (end_pfn_map >> (PMD_SHIFT-PAGE_SHIFT)))
+ set_memory_4k((unsigned long)__va(tseg), 1);
+ }

void __cpuinit detect_ht(struct cpuinfo_x86 *c)
Index: linux/include/asm-x86/msr-index.h
--- linux.orig/include/asm-x86/msr-index.h
+++ linux/include/asm-x86/msr-index.h
@@ -109,6 +109,7 @@
#define MSR_K8_SYSCFG 0xc0010010
#define MSR_K8_HWCR 0xc0010015
#define MSR_K8_ENABLE_C1E 0xc0010055
+#define MSR_K8_TSEG_ADDR 0xc0010112
#define K8_MTRRFIXRANGE_DRAM_ENABLE 0x00040000 /* MtrrFixDramEn bit */
#define K8_MTRRFIXRANGE_DRAM_MODIFY 0x00080000 /* MtrrFixDramModEn bit */
#define K8_MTRR_RDMEM_WRMEM_MASK 0x18181818 /* Mask: RdMem|WrMem */

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