Howdy,
Attached patch implements lazy-fpu save/restore for VT. VMEXIT time
improves by about 10% (~550 cycles). I had to do a couple more things
to get it working than I had to do with SVM. I changed the CR0 host
mask to be all 1's so that any attempt to write to CR0 causes a VMEXIT.
I don't think there are any remaining bits now that we want to trap TS
that are safe for the guest to access and are in the fast-paths.
Since we're trapping TS, I had to implement CLTS exit handling.
vcpu->cr0 also had a rather bizarre life cycle. After a set_cr0, it was
a proper shadow of the guest's CR0. However, after a decache_cr0, it
would contain the host's version of the bits covered by the CR0 host
mask so it was no longer a proper shadow.
I got rid of the CR0 caching and made vcpu->cr0 always be equivalent to
CR0_READ_SHADOW. Once these changes were made, the rest of the patch
was much like the SVM one.
Regards,
Anthony Liguori
From: Anthony Liguori <[EMAIL PROTECTED]>
Subject: [PATCH] Lazy FPU save/restore for VT
Lazy FPU save/restore for VT
Signed-off-by: Anthony Liguori <[EMAIL PROTECTED]>
Index: kernel/drivers/kvm/vmx.c
===================================================================
--- kernel.orig/drivers/kvm/vmx.c 2007-04-26 08:53:54.584362024 -0500
+++ kernel/drivers/kvm/vmx.c 2007-04-26 10:34:49.693845464 -0500
@@ -216,6 +216,16 @@
#endif
}
+static void vmcs_clear_bits(unsigned long field, u32 mask)
+{
+ vmcs_writel(field, vmcs_readl(field) & ~mask);
+}
+
+static void vmcs_set_bits(unsigned long field, u32 mask)
+{
+ vmcs_writel(field, vmcs_readl(field) | mask);
+}
+
/*
* Switches to specified vcpu, until a matching vcpu_put(), but assumes
* vcpu mutex is already taken.
@@ -810,11 +820,8 @@
#endif
-static void vmx_decache_cr0_cr4_guest_bits(struct kvm_vcpu *vcpu)
+static void vmx_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
{
- vcpu->cr0 &= KVM_GUEST_CR0_MASK;
- vcpu->cr0 |= vmcs_readl(GUEST_CR0) & ~KVM_GUEST_CR0_MASK;
-
vcpu->cr4 &= KVM_GUEST_CR4_MASK;
vcpu->cr4 |= vmcs_readl(GUEST_CR4) & ~KVM_GUEST_CR4_MASK;
}
@@ -836,6 +843,11 @@
}
#endif
+ if (!(cr0 & CR0_TS_MASK)) {
+ vcpu->fpu_active = 1;
+ vmcs_clear_bits(EXCEPTION_BITMAP, CR0_TS_MASK);
+ }
+
vmcs_writel(CR0_READ_SHADOW, cr0);
vmcs_writel(GUEST_CR0,
(cr0 & ~KVM_GUEST_CR0_MASK) | KVM_VM_CR0_ALWAYS_ON);
@@ -845,6 +857,12 @@
static void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
{
vmcs_writel(GUEST_CR3, cr3);
+
+ if (!(vcpu->cr0 & CR0_TS_MASK)) {
+ vcpu->fpu_active = 0;
+ vmcs_set_bits(GUEST_CR0, CR0_TS_MASK);
+ vmcs_set_bits(EXCEPTION_BITMAP, 1 << NM_VECTOR);
+ }
}
static void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
@@ -1205,7 +1223,7 @@
vmcs_writel(TPR_THRESHOLD, 0);
#endif
- vmcs_writel(CR0_GUEST_HOST_MASK, KVM_GUEST_CR0_MASK);
+ vmcs_writel(CR0_GUEST_HOST_MASK, ~0UL);
vmcs_writel(CR4_GUEST_HOST_MASK, KVM_GUEST_CR4_MASK);
vcpu->cr0 = 0x60000010;
@@ -1367,10 +1385,18 @@
set_bit(irq / BITS_PER_LONG, &vcpu->irq_summary);
}
- if ((intr_info & INTR_INFO_INTR_TYPE_MASK) == 0x200) { /* nmi */
+ switch (intr_info & INTR_INFO_VECTOR_MASK) {
+ case NMI_VECTOR:
asm ("int $2");
return 1;
+ case NM_VECTOR:
+ vcpu->fpu_active = 1;
+ vmcs_clear_bits(EXCEPTION_BITMAP, 1 << NM_VECTOR);
+ if (!(vcpu->cr0 & CR0_TS_MASK))
+ vmcs_clear_bits(GUEST_CR0, CR0_TS_MASK);
+ return 1;
}
+
error_code = 0;
rip = vmcs_readl(GUEST_RIP);
if (intr_info & INTR_INFO_DELIEVER_CODE_MASK)
@@ -1557,6 +1583,15 @@
return 1;
};
break;
+ case 2: /* clts */
+ vcpu_load_rsp_rip(vcpu);
+ vcpu->fpu_active = 1;
+ vmcs_clear_bits(EXCEPTION_BITMAP, 1 << NM_VECTOR);
+ vmcs_clear_bits(GUEST_CR0, CR0_TS_MASK);
+ vcpu->cr0 &= ~CR0_TS_MASK;
+ vmcs_writel(CR0_READ_SHADOW, vcpu->cr0);
+ skip_emulated_instruction(vcpu);
+ return 1;
case 1: /*mov from cr*/
switch (cr) {
case 3:
@@ -1804,8 +1839,10 @@
if (vcpu->guest_debug.enabled)
kvm_guest_debug_pre(vcpu);
- fx_save(vcpu->host_fx_image);
- fx_restore(vcpu->guest_fx_image);
+ if (vcpu->fpu_active) {
+ fx_save(vcpu->host_fx_image);
+ fx_restore(vcpu->guest_fx_image);
+ }
#ifdef CONFIG_X86_64
if (is_long_mode(vcpu)) {
@@ -1963,8 +2000,11 @@
}
#endif
- fx_save(vcpu->guest_fx_image);
- fx_restore(vcpu->host_fx_image);
+ if (vcpu->fpu_active) {
+ fx_save(vcpu->guest_fx_image);
+ fx_restore(vcpu->host_fx_image);
+ }
+
vcpu->interrupt_window_open = (vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & 3) == 0;
asm ("mov %0, %%ds; mov %0, %%es" : : "r"(__USER_DS));
@@ -2076,6 +2116,7 @@
vmcs_clear(vmcs);
vcpu->vmcs = vmcs;
vcpu->launched = 0;
+ vcpu->fpu_active = 1;
return 0;
@@ -2112,7 +2153,7 @@
.get_segment = vmx_get_segment,
.set_segment = vmx_set_segment,
.get_cs_db_l_bits = vmx_get_cs_db_l_bits,
- .decache_cr0_cr4_guest_bits = vmx_decache_cr0_cr4_guest_bits,
+ .decache_cr4_guest_bits = vmx_decache_cr4_guest_bits,
.set_cr0 = vmx_set_cr0,
.set_cr3 = vmx_set_cr3,
.set_cr4 = vmx_set_cr4,
Index: kernel/drivers/kvm/kvm.h
===================================================================
--- kernel.orig/drivers/kvm/kvm.h 2007-04-26 10:17:29.931913304 -0500
+++ kernel/drivers/kvm/kvm.h 2007-04-26 10:36:00.420093440 -0500
@@ -63,6 +63,9 @@
#define FX_BUF_SIZE (2 * FX_IMAGE_SIZE + FX_IMAGE_ALIGN)
#define DE_VECTOR 0
+#ifdef CONFIG_X86_64
+#define NMI_VECTOR 2
+#endif
#define NM_VECTOR 7
#define DF_VECTOR 8
#define TS_VECTOR 10
@@ -397,7 +400,7 @@
void (*set_segment)(struct kvm_vcpu *vcpu,
struct kvm_segment *var, int seg);
void (*get_cs_db_l_bits)(struct kvm_vcpu *vcpu, int *db, int *l);
- void (*decache_cr0_cr4_guest_bits)(struct kvm_vcpu *vcpu);
+ void (*decache_cr4_guest_bits)(struct kvm_vcpu *vcpu);
void (*set_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
void (*set_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);
void (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
Index: kernel/drivers/kvm/kvm_main.c
===================================================================
--- kernel.orig/drivers/kvm/kvm_main.c 2007-04-26 10:35:03.087809272 -0500
+++ kernel/drivers/kvm/kvm_main.c 2007-04-26 10:35:50.944533944 -0500
@@ -510,7 +510,6 @@
void lmsw(struct kvm_vcpu *vcpu, unsigned long msw)
{
- kvm_arch_ops->decache_cr0_cr4_guest_bits(vcpu);
set_cr0(vcpu, (vcpu->cr0 & ~0x0ful) | (msw & 0x0f));
}
EXPORT_SYMBOL_GPL(lmsw);
@@ -1117,7 +1116,6 @@
{
unsigned long cr0;
- kvm_arch_ops->decache_cr0_cr4_guest_bits(vcpu);
cr0 = vcpu->cr0 & ~CR0_TS_MASK;
kvm_arch_ops->set_cr0(vcpu, cr0);
return X86EMUL_CONTINUE;
@@ -1318,7 +1316,7 @@
unsigned long realmode_get_cr(struct kvm_vcpu *vcpu, int cr)
{
- kvm_arch_ops->decache_cr0_cr4_guest_bits(vcpu);
+ kvm_arch_ops->decache_cr4_guest_bits(vcpu);
switch (cr) {
case 0:
return vcpu->cr0;
@@ -1934,7 +1932,7 @@
sregs->gdt.limit = dt.limit;
sregs->gdt.base = dt.base;
- kvm_arch_ops->decache_cr0_cr4_guest_bits(vcpu);
+ kvm_arch_ops->decache_cr4_guest_bits(vcpu);
sregs->cr0 = vcpu->cr0;
sregs->cr2 = vcpu->cr2;
sregs->cr3 = vcpu->cr3;
@@ -1985,7 +1983,7 @@
#endif
vcpu->apic_base = sregs->apic_base;
- kvm_arch_ops->decache_cr0_cr4_guest_bits(vcpu);
+ kvm_arch_ops->decache_cr4_guest_bits(vcpu);
mmu_reset_needed |= vcpu->cr0 != sregs->cr0;
kvm_arch_ops->set_cr0(vcpu, sregs->cr0);
Index: kernel/drivers/kvm/svm.c
===================================================================
--- kernel.orig/drivers/kvm/svm.c 2007-04-26 10:35:03.019819608 -0500
+++ kernel/drivers/kvm/svm.c 2007-04-26 10:35:16.142824608 -0500
@@ -738,7 +738,7 @@
vcpu->svm->vmcb->save.gdtr.base = dt->base ;
}
-static void svm_decache_cr0_cr4_guest_bits(struct kvm_vcpu *vcpu)
+static void svm_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
{
}
@@ -1759,7 +1759,7 @@
.get_segment = svm_get_segment,
.set_segment = svm_set_segment,
.get_cs_db_l_bits = svm_get_cs_db_l_bits,
- .decache_cr0_cr4_guest_bits = svm_decache_cr0_cr4_guest_bits,
+ .decache_cr4_guest_bits = svm_decache_cr4_guest_bits,
.set_cr0 = svm_set_cr0,
.set_cr3 = svm_set_cr3,
.set_cr4 = svm_set_cr4,
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