x86, amd: Avoid cache aliasing penalties on AMD family 15h

This patch provides performance tuning for the "Bulldozer" CPU. With its
shared instruction cache there is a chance of generating an excessive
number of cache cross-invalidates when running specific workloads on the
cores of a compute module.

This excessive amount of cross-invalidations can be observed if cache
lines backed by shared physical memory alias in bits [14:12] of their
virtual addresses, as those bits are used for the index generation.

This patch addresses the issue by clearing all the bits in the [14:12]
slice of the file mapping's virtual address at generation time, thus
forcing those bits the same for all mappings of a single shared library
across processes and, in doing so, avoids instruction cache aliases.

It also adds the command line option "align_va_addr=(32|64|on|off)" with
which virtual address alignment can be enabled for 32-bit or 64-bit x86
individually, or both, or be completely disabled.

This change leaves virtual region address allocation on other families
and/or vendors unaffected.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Link: http://lkml.kernel.org/r/1312550110-24160-2-git-send-email-bp@amd64.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index b13ed39..b0234bc 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -458,6 +458,19 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
 					"with P0 frequency!\n");
 		}
 	}
+
+	if (c->x86 == 0x15) {
+		unsigned long upperbit;
+		u32 cpuid, assoc;
+
+		cpuid	 = cpuid_edx(0x80000005);
+		assoc	 = cpuid >> 16 & 0xff;
+		upperbit = ((cpuid >> 24) << 10) / assoc;
+
+		va_align.mask	  = (upperbit - 1) & PAGE_MASK;
+		va_align.flags    = ALIGN_VA_32 | ALIGN_VA_64;
+
+	}
 }
 
 static void __cpuinit init_amd(struct cpuinfo_x86 *c)