From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: [PATCH 12/18] KVM: VMX: Only save/restore MSR_K6_STAR if necessary Date: Thu, 26 Apr 2007 12:22:12 +0300 Message-ID: <11775793381764-git-send-email-avi@qumranet.com> References: <11775793382353-git-send-email-avi@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Return-path: In-Reply-To: <11775793382353-git-send-email-avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Intel hosts only support syscall/sysret in long more (and only if efer.sce is enabled), so only reload the related MSR_K6_STAR if the guest will actually be able to use it. This reduces vmexit cost by about 500 cycles (6400 -> 5870) on my setup. Signed-off-by: Avi Kivity --- drivers/kvm/vmx.c | 16 ++++++++++++++++ 1 files changed, 16 insertions(+), 0 deletions(-) diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c index b61d4dd..37537af 100644 --- a/drivers/kvm/vmx.c +++ b/drivers/kvm/vmx.c @@ -69,6 +69,10 @@ static struct kvm_vmx_segment_field { VMX_SEGMENT_FIELD(LDTR), }; +/* + * Keep MSR_K6_STAR at the end, as setup_msrs() will try to optimize it + * away by decrementing the array size. + */ static const u32 vmx_msr_index[] = { #ifdef CONFIG_X86_64 MSR_SYSCALL_MASK, MSR_LSTAR, MSR_CSTAR, MSR_KERNEL_GS_BASE, @@ -323,6 +327,18 @@ static void setup_msrs(struct kvm_vcpu *vcpu) nr_skip = NR_64BIT_MSRS; nr_good_msrs = vcpu->nmsrs - nr_skip; + /* + * MSR_K6_STAR is only needed on long mode guests, and only + * if efer.sce is enabled. + */ + if (find_msr_entry(vcpu, MSR_K6_STAR)) { + --nr_good_msrs; +#ifdef CONFIG_X86_64 + if (is_long_mode(vcpu) && (vcpu->shadow_efer & EFER_SCE)) + ++nr_good_msrs; +#endif + } + vmcs_writel(VM_ENTRY_MSR_LOAD_ADDR, virt_to_phys(vcpu->guest_msrs + nr_skip)); vmcs_writel(VM_EXIT_MSR_STORE_ADDR, -- 1.5.0.6 ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/