From: Boris Ostrovsky Subject: [PATCH] AMD: Enable WC+ memory type on family 10 processors Date: Thu, 17 Jan 2013 13:44:03 -0500 Message-ID: <1963e398ba0f5dd61818.1358448243@linux-vgzc.amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: xen-devel@lists.xen.org Cc: boris.ostrovsky@amd.com List-Id: xen-devel@lists.xenproject.org # HG changeset patch # User Boris Ostrovsky # Date 1358429914 18000 # Node ID 1963e398ba0f5dd61818d92400c7b07a32f6da4b # Parent b6195e277da52129d5d79f29ccac0e7290643e37 AMD: Enable WC+ memory type on family 10 processors In some cases BIOS may not enable WC+ memory type on family 10 processors, instead converting what would be WC+ memory to CD type. On guests using nested pages this could result in performance degradation. This patch enables WC+. Signed-off-by: Boris Ostrovsky diff -r b6195e277da5 -r 1963e398ba0f xen/arch/x86/cpu/amd.c --- a/xen/arch/x86/cpu/amd.c Wed Jan 16 14:15:44 2013 +0000 +++ b/xen/arch/x86/cpu/amd.c Thu Jan 17 08:38:34 2013 -0500 @@ -495,6 +495,18 @@ static void __devinit init_amd(struct cp set_bit(X86_FEATURE_ARAT, c->x86_capability); /* + * On family 10h BIOS may not have properly enabled WC+ support, causing + * it to be converted to CD memtype. This may result in performance + * degradation for certain nested-paging guests. Prevent this conversion + * by enabling WC+ support through MSRC001_1024A[24] = 0 + */ + if (c->x86 == 0x10) { + rdmsr_safe(0xc001102a, value); + value &= ~(1ULL << 24); + wrmsr_safe(0xc001102a, value); + } + + /* * Prior to Family 0x14, perf counters are not reset during warm reboot. * We have to reset them manually. */