IA32_MISC_ENABLE MSR has two bits that affect the actual results which can be
observed by the guest: fast string enable, and FOPCODE compatibility. Guests
may wish to change the default settings of these bits.
Linux usually enables fast-string by default. However, when "fast string" is
enabled data breakpoints are only recognized on boundaries between data-groups.
On some old CPUs enabling fast-string also resulted in single-step not
occurring upon each iteration.
FOPCODE compatibility can be used to analyze program performance by recording
the last instruction executed before FSAVE/FSTENV/FXSAVE.
This patch saves and restores these bits in IA32_MISC_ENABLE if they are
supported upon entry to guest and exit to userspace respectively. To avoid
possible issues, fast-string can only be enabled by the guest if the host
enabled them. The physical CPU version is checked to ensure no shared bits are
reconfigured in the process.
Signed-off-by: Nadav Amit <namit@xxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/svm.c | 7 ++++++
arch/x86/kvm/vmx.c | 56 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.c | 2 +-
4 files changed, 65 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4bda61b..879b930 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -699,6 +699,7 @@ struct kvm_x86_ops {
void (*set_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);
int (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
void (*set_efer)(struct kvm_vcpu *vcpu, u64 efer);
+ void (*set_misc_enable)(struct kvm_vcpu *vcpu, u64 data);
void (*get_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
void (*set_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
void (*get_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 1f49c86..378e50e 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -480,6 +480,11 @@ static void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
mark_dirty(to_svm(vcpu)->vmcb, VMCB_CR);
}
+static void svm_set_misc_enable(struct kvm_vcpu *vcpu, u64 data)
+{
+ vcpu->arch.ia32_misc_enable_msr = data;
+}
+
static int is_external_interrupt(u32 info)
{
info &= SVM_EVTINJ_TYPE_MASK | SVM_EVTINJ_VALID;
@@ -1152,6 +1157,7 @@ static void init_vmcb(struct vcpu_svm *svm)
init_sys_seg(&save->tr, SEG_TYPE_BUSY_TSS16);
svm_set_efer(&svm->vcpu, 0);
+ svm_set_misc_enable(&svm->vcpu, 0);
save->dr6 = 0xffff0ff0;
kvm_set_rflags(&svm->vcpu, 2);
save->rip = 0x0000fff0;
@@ -4338,6 +4344,7 @@ static struct kvm_x86_ops svm_x86_ops = {
.set_cr3 = svm_set_cr3,
.set_cr4 = svm_set_cr4,
.set_efer = svm_set_efer,
+ .set_misc_enable = svm_set_misc_enable,
.get_idt = svm_get_idt,
.set_idt = svm_set_idt,
.get_gdt = svm_get_gdt,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 45bab55..2d2efd0 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -809,6 +809,8 @@ static const struct kvm_vmx_segment_field {
};
static u64 host_efer;
+static u64 host_misc_enable;
+static u64 guest_misc_enable_mask;
static void ept_save_pdptrs(struct kvm_vcpu *vcpu);
@@ -1609,6 +1611,33 @@ static void reload_tss(void)
load_TR_desc();
}
+static void __init update_guest_misc_enable_mask(void)
+{
+ /* Calculating which of the IA32_MISC_ENABLE bits should be reflected
+ in hardware */
+ struct cpuinfo_x86 *c = &boot_cpu_data;
+ u64 data;
+
+ guest_misc_enable_mask = 0;
+
+ /* Core/Atom architecture share fast-string and x86 compat */
+ if (c->x86 != 6 || c->x86_model < 0xd)
+ return;
+
+ if (rdmsrl_safe(MSR_IA32_MISC_ENABLE, &data) < 0)
+ return;
+ if (boot_cpu_has(X86_FEATURE_REP_GOOD))
+ guest_misc_enable_mask |= MSR_IA32_MISC_ENABLE_FAST_STRING;
+
+ preempt_disable();
+ if (wrmsrl_safe(MSR_IA32_MISC_ENABLE,
+ data | MSR_IA32_MISC_ENABLE_X87_COMPAT) >= 0) {
+ guest_misc_enable_mask |= MSR_IA32_MISC_ENABLE_X87_COMPAT;
+ wrmsrl(MSR_IA32_MISC_ENABLE, data);
+ }
+ preempt_enable();
+}
+
static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset)
{
u64 guest_efer;
@@ -3126,6 +3155,8 @@ static __init int hardware_setup(void)
if (!cpu_has_vmx_apicv())
enable_apicv = 0;
+ update_guest_misc_enable_mask();
+
if (enable_apicv)
kvm_x86_ops->update_cr8_intercept = NULL;
else {
@@ -3315,6 +3346,28 @@ static void vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
setup_msrs(vmx);
}
+static void vmx_set_misc_enable(struct kvm_vcpu *vcpu, u64 data)
+{
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+ vcpu->arch.ia32_misc_enable_msr = data;
+
+ if (guest_misc_enable_mask == 0)
+ return;
+ clear_atomic_switch_msr(vmx, MSR_IA32_MISC_ENABLE);
+ if (((data ^ host_misc_enable) & guest_misc_enable_mask) == 0)
+ return;
+
+ /*
+ * If the guest has different value, we want to load it atomically
+ * since it can affect host performance
+ */
+ data &= guest_misc_enable_mask;
+ data |= (host_misc_enable & ~guest_misc_enable_mask);
+ add_atomic_switch_msr(vmx, MSR_IA32_MISC_ENABLE, data,
+ host_misc_enable);
+}
+
#ifdef CONFIG_X86_64
static void enter_lmode(struct kvm_vcpu *vcpu)
@@ -4555,6 +4608,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
vmx_set_cr0(&vmx->vcpu, kvm_read_cr0(vcpu)); /* enter rmode */
vmx_set_cr4(&vmx->vcpu, 0);
vmx_set_efer(&vmx->vcpu, 0);
+ vmx_set_misc_enable(&vmx->vcpu, 0);
vmx_fpu_activate(&vmx->vcpu);
update_exception_bitmap(&vmx->vcpu);
@@ -8883,6 +8937,7 @@ static struct kvm_x86_ops vmx_x86_ops = {
.set_cr3 = vmx_set_cr3,
.set_cr4 = vmx_set_cr4,
.set_efer = vmx_set_efer,
+ .set_misc_enable = vmx_set_misc_enable,
.get_idt = vmx_get_idt,
.set_idt = vmx_set_idt,
.get_gdt = vmx_get_gdt,
@@ -8961,6 +9016,7 @@ static int __init vmx_init(void)
int r, i, msr;
rdmsrl_safe(MSR_EFER, &host_efer);
+ rdmsrl_safe(MSR_IA32_MISC_ENABLE, &host_misc_enable);
for (i = 0; i < ARRAY_SIZE(vmx_msr_index); ++i)
kvm_define_shared_msr(i, vmx_msr_index[i]);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5f5edb6..72d449a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2096,7 +2096,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
}
break;
case MSR_IA32_MISC_ENABLE:
- vcpu->arch.ia32_misc_enable_msr = data;
+ kvm_x86_ops->set_misc_enable(vcpu, data);
break;
case MSR_KVM_WALL_CLOCK_NEW:
case MSR_KVM_WALL_CLOCK:
--
1.9.1
--
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