KVM: VMX: Enable MSR Bitmap feature

MSR Bitmap controls whether the accessing of an MSR causes VM Exit.
Eliminating exits on automatically saved and restored MSRs yields a
small performance gain.

Signed-off-by: Sheng Yang <sheng.yang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 60 insertions, 7 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index cbca46acfac3..87eee7a7f16e 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -91,6 +91,7 @@ static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
 
 static struct page *vmx_io_bitmap_a;
 static struct page *vmx_io_bitmap_b;
+static struct page *vmx_msr_bitmap;
 
 static DECLARE_BITMAP(vmx_vpid_bitmap, VMX_NR_VPIDS);
 static DEFINE_SPINLOCK(vmx_vpid_lock);
@@ -185,6 +186,11 @@ static inline int is_external_interrupt(u32 intr_info)
                 == (INTR_TYPE_EXT_INTR | INTR_INFO_VALID_MASK);
 }
 
+static inline int cpu_has_vmx_msr_bitmap(void)
+{
+        return (vmcs_config.cpu_based_exec_ctrl & CPU_BASED_USE_MSR_BITMAPS);
+}
+
 static inline int cpu_has_vmx_tpr_shadow(void)
 {
         return (vmcs_config.cpu_based_exec_ctrl & CPU_BASED_TPR_SHADOW);
@@ -1001,6 +1007,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
               CPU_BASED_MOV_DR_EXITING |
               CPU_BASED_USE_TSC_OFFSETING;
         opt = CPU_BASED_TPR_SHADOW |
+              CPU_BASED_USE_MSR_BITMAPS |
               CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
         if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_PROCBASED_CTLS,
                                 &_cpu_based_exec_control) < 0)
@@ -1575,6 +1582,30 @@ static void allocate_vpid(struct vcpu_vmx *vmx)
         spin_unlock(&vmx_vpid_lock);
 }
 
+void vmx_disable_intercept_for_msr(struct page *msr_bitmap, u32 msr)
+{
+        void *va;
+
+        if (!cpu_has_vmx_msr_bitmap())
+                return;
+
+        /*
+         * See Intel PRM Vol. 3, 20.6.9 (MSR-Bitmap Address). Early manuals
+         * have the write-low and read-high bitmap offsets the wrong way round.
+         * We can control MSRs 0x00000000-0x00001fff and 0xc0000000-0xc0001fff.
+         */
+        va = kmap(msr_bitmap);
+        if (msr <= 0x1fff) {
+                __clear_bit(msr, va + 0x000); /* read-low */
+                __clear_bit(msr, va + 0x800); /* write-low */
+        } else if ((msr >= 0xc0000000) && (msr <= 0xc0001fff)) {
+                msr &= 0x1fff;
+                __clear_bit(msr, va + 0x400); /* read-high */
+                __clear_bit(msr, va + 0xc00); /* write-high */
+        }
+        kunmap(msr_bitmap);
+}
+
 /*
  * Sets up the vmcs for emulated real mode.
  */
@@ -1592,6 +1623,9 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
         vmcs_write64(IO_BITMAP_A, page_to_phys(vmx_io_bitmap_a));
         vmcs_write64(IO_BITMAP_B, page_to_phys(vmx_io_bitmap_b));
 
+        if (cpu_has_vmx_msr_bitmap())
+                vmcs_write64(MSR_BITMAP, page_to_phys(vmx_msr_bitmap));
+
         vmcs_write64(VMCS_LINK_POINTER, -1ull); /* 22.3.1.5 */
 
         /* Control */
@@ -2728,7 +2762,7 @@ static struct kvm_x86_ops vmx_x86_ops = {
 
 static int __init vmx_init(void)
 {
-        void *iova;
+        void *va;
         int r;
 
         vmx_io_bitmap_a = alloc_page(GFP_KERNEL | __GFP_HIGHMEM);
@@ -2741,30 +2775,48 @@ static int __init vmx_init(void)
                 goto out;
         }
 
+        vmx_msr_bitmap = alloc_page(GFP_KERNEL | __GFP_HIGHMEM);
+        if (!vmx_msr_bitmap) {
+                r = -ENOMEM;
+                goto out1;
+        }
+
         /*
          * Allow direct access to the PC debug port (it is often used for I/O
          * delays, but the vmexits simply slow things down).
          */
-        iova = kmap(vmx_io_bitmap_a);
-        memset(iova, 0xff, PAGE_SIZE);
-        clear_bit(0x80, iova);
+        va = kmap(vmx_io_bitmap_a);
+        memset(va, 0xff, PAGE_SIZE);
+        clear_bit(0x80, va);
         kunmap(vmx_io_bitmap_a);
 
-        iova = kmap(vmx_io_bitmap_b);
-        memset(iova, 0xff, PAGE_SIZE);
+        va = kmap(vmx_io_bitmap_b);
+        memset(va, 0xff, PAGE_SIZE);
         kunmap(vmx_io_bitmap_b);
 
+        va = kmap(vmx_msr_bitmap);
+        memset(va, 0xff, PAGE_SIZE);
+        kunmap(vmx_msr_bitmap);
+
         set_bit(0, vmx_vpid_bitmap); /* 0 is reserved for host */
 
         r = kvm_init(&vmx_x86_ops, sizeof(struct vcpu_vmx), THIS_MODULE);
         if (r)
-                goto out1;
+                goto out2;
+
+        vmx_disable_intercept_for_msr(vmx_msr_bitmap, MSR_FS_BASE);
+        vmx_disable_intercept_for_msr(vmx_msr_bitmap, MSR_GS_BASE);
+        vmx_disable_intercept_for_msr(vmx_msr_bitmap, MSR_IA32_SYSENTER_CS);
+        vmx_disable_intercept_for_msr(vmx_msr_bitmap, MSR_IA32_SYSENTER_ESP);
+        vmx_disable_intercept_for_msr(vmx_msr_bitmap, MSR_IA32_SYSENTER_EIP);
 
         if (bypass_guest_pf)
                 kvm_mmu_set_nonpresent_ptes(~0xffeull, 0ull);
 
         return 0;
 
+out2:
+        __free_page(vmx_msr_bitmap);
 out1:
         __free_page(vmx_io_bitmap_b);
 out:
@@ -2774,6 +2826,7 @@ out:
 
 static void __exit vmx_exit(void)
 {
+        __free_page(vmx_msr_bitmap);
         __free_page(vmx_io_bitmap_b);
         __free_page(vmx_io_bitmap_a);