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, 9 insertions, 0 deletions

diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 7abd2be..caa42ce 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -69,6 +69,15 @@ static unsigned long vdso_addr(unsigned long start, unsigned len)
 	addr = start + (offset << PAGE_SHIFT);
 	if (addr >= end)
 		addr = end;
+
+	/*
+	 * page-align it here so that get_unmapped_area doesn't
+	 * align it wrongfully again to the next page. addr can come in 4K
+	 * unaligned here as a result of stack start randomization.
+	 */
+	addr = PAGE_ALIGN(addr);
+	addr = align_addr(addr, NULL, ALIGN_VDSO);
+
 	return addr;
 }