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authorPaolo Bonzini <pbonzini@redhat.com>2017-12-13 14:16:30 +0100
committerRadim Krčmář <rkrcmar@redhat.com>2018-01-16 16:52:52 +0100
commitc992384bde84fb2f0318bdb4f6c710605dd7a217 (patch)
tree60f91e72baf56050435eccd642b4e04067e8bbb9
parent1f6e5b25643e539e55a4c7553e4be6562c88fb76 (diff)
KVM: vmx: speed up MSR bitmap merge
The bulk of the MSR bitmap is either immutable, or can be copied from the L1 bitmap. By initializing it at VMXON time, and copying the mutable parts one long at a time on vmentry (rather than one bit), about 4000 clock cycles (30%) can be saved on a nested VMLAUNCH/VMRESUME. The resulting for loop only has four iterations, so it is cheap enough to reinitialize the MSR write bitmaps on every iteration, and it makes the code simpler. Suggested-by: Jim Mattson <jmattson@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
-rw-r--r--arch/x86/kvm/vmx.c78
1 files changed, 42 insertions, 36 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1f4a3037b99e..71b2c9354423 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4972,11 +4972,6 @@ static void nested_vmx_disable_intercept_for_msr(unsigned long *msr_bitmap_l1,
{
int f = sizeof(unsigned long);
- if (!cpu_has_vmx_msr_bitmap()) {
- WARN_ON(1);
- 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.
@@ -7177,6 +7172,7 @@ static int enter_vmx_operation(struct kvm_vcpu *vcpu)
(unsigned long *)__get_free_page(GFP_KERNEL);
if (!vmx->nested.msr_bitmap)
goto out_msr_bitmap;
+ memset(vmx->nested.msr_bitmap, 0xff, PAGE_SIZE);
}
vmx->nested.cached_vmcs12 = kmalloc(VMCS12_SIZE, GFP_KERNEL);
@@ -9844,8 +9840,8 @@ static void vmx_inject_page_fault_nested(struct kvm_vcpu *vcpu,
}
}
-static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu,
- struct vmcs12 *vmcs12);
+static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
+ struct vmcs12 *vmcs12);
static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu,
struct vmcs12 *vmcs12)
@@ -9934,11 +9930,7 @@ static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu,
(unsigned long)(vmcs12->posted_intr_desc_addr &
(PAGE_SIZE - 1)));
}
- if (cpu_has_vmx_msr_bitmap() &&
- nested_cpu_has(vmcs12, CPU_BASED_USE_MSR_BITMAPS) &&
- nested_vmx_merge_msr_bitmap(vcpu, vmcs12))
- ;
- else
+ if (!nested_vmx_prepare_msr_bitmap(vcpu, vmcs12))
vmcs_clear_bits(CPU_BASED_VM_EXEC_CONTROL,
CPU_BASED_USE_MSR_BITMAPS);
}
@@ -10006,14 +9998,19 @@ static int nested_vmx_check_tpr_shadow_controls(struct kvm_vcpu *vcpu,
* Merge L0's and L1's MSR bitmap, return false to indicate that
* we do not use the hardware.
*/
-static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu,
- struct vmcs12 *vmcs12)
+static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
+ struct vmcs12 *vmcs12)
{
int msr;
struct page *page;
unsigned long *msr_bitmap_l1;
unsigned long *msr_bitmap_l0 = to_vmx(vcpu)->nested.msr_bitmap;
+ /* Nothing to do if the MSR bitmap is not in use. */
+ if (!cpu_has_vmx_msr_bitmap() ||
+ !nested_cpu_has(vmcs12, CPU_BASED_USE_MSR_BITMAPS))
+ return false;
+
/* This shortcut is ok because we support only x2APIC MSRs so far. */
if (!nested_cpu_has_virt_x2apic_mode(vmcs12))
return false;
@@ -10021,32 +10018,41 @@ static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu,
page = kvm_vcpu_gpa_to_page(vcpu, vmcs12->msr_bitmap);
if (is_error_page(page))
return false;
- msr_bitmap_l1 = (unsigned long *)kmap(page);
- memset(msr_bitmap_l0, 0xff, PAGE_SIZE);
+ msr_bitmap_l1 = (unsigned long *)kmap(page);
+ if (nested_cpu_has_apic_reg_virt(vmcs12)) {
+ /*
+ * L0 need not intercept reads for MSRs between 0x800 and 0x8ff, it
+ * just lets the processor take the value from the virtual-APIC page;
+ * take those 256 bits directly from the L1 bitmap.
+ */
+ for (msr = 0x800; msr <= 0x8ff; msr += BITS_PER_LONG) {
+ unsigned word = msr / BITS_PER_LONG;
+ msr_bitmap_l0[word] = msr_bitmap_l1[word];
+ msr_bitmap_l0[word + (0x800 / sizeof(long))] = ~0;
+ }
+ } else {
+ for (msr = 0x800; msr <= 0x8ff; msr += BITS_PER_LONG) {
+ unsigned word = msr / BITS_PER_LONG;
+ msr_bitmap_l0[word] = ~0;
+ msr_bitmap_l0[word + (0x800 / sizeof(long))] = ~0;
+ }
+ }
- if (nested_cpu_has_virt_x2apic_mode(vmcs12)) {
- if (nested_cpu_has_apic_reg_virt(vmcs12))
- for (msr = 0x800; msr <= 0x8ff; msr++)
- nested_vmx_disable_intercept_for_msr(
- msr_bitmap_l1, msr_bitmap_l0,
- msr, MSR_TYPE_R);
+ nested_vmx_disable_intercept_for_msr(
+ msr_bitmap_l1, msr_bitmap_l0,
+ APIC_BASE_MSR + (APIC_TASKPRI >> 4),
+ MSR_TYPE_W);
+ if (nested_cpu_has_vid(vmcs12)) {
nested_vmx_disable_intercept_for_msr(
- msr_bitmap_l1, msr_bitmap_l0,
- APIC_BASE_MSR + (APIC_TASKPRI >> 4),
- MSR_TYPE_R | MSR_TYPE_W);
-
- if (nested_cpu_has_vid(vmcs12)) {
- nested_vmx_disable_intercept_for_msr(
- msr_bitmap_l1, msr_bitmap_l0,
- APIC_BASE_MSR + (APIC_EOI >> 4),
- MSR_TYPE_W);
- nested_vmx_disable_intercept_for_msr(
- msr_bitmap_l1, msr_bitmap_l0,
- APIC_BASE_MSR + (APIC_SELF_IPI >> 4),
- MSR_TYPE_W);
- }
+ msr_bitmap_l1, msr_bitmap_l0,
+ APIC_BASE_MSR + (APIC_EOI >> 4),
+ MSR_TYPE_W);
+ nested_vmx_disable_intercept_for_msr(
+ msr_bitmap_l1, msr_bitmap_l0,
+ APIC_BASE_MSR + (APIC_SELF_IPI >> 4),
+ MSR_TYPE_W);
}
kunmap(page);
kvm_release_page_clean(page);