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KVM: VMX: Add proper cache tracking for CR4
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Move CR4 caching into the standard register caching mechanism in order
to take advantage of the availability checks provided by regs_avail.
This avoids multiple VMREADs and retpolines (when configured) during
nested VMX transitions as kvm_read_cr4_bits() is invoked multiple times
on each transition, e.g. when stuffing CR0 and CR3.

As an added bonus, this eliminates a kvm_x86_ops hook, saves a retpoline
on SVM when reading CR4, and squashes the confusing naming discrepancy
of "cache_reg" vs. "decache_cr4_guest_bits".

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200502043234.12481-7-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Sean Christopherson authored and Paolo Bonzini committed May 13, 2020
1 parent 0cc6920 commit f98c1e7
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Showing 5 changed files with 14 additions and 17 deletions.
2 changes: 1 addition & 1 deletion arch/x86/include/asm/kvm_host.h
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Original file line number Diff line number Diff line change
Expand Up @@ -168,6 +168,7 @@ enum kvm_reg {

VCPU_EXREG_PDPTR = NR_VCPU_REGS,
VCPU_EXREG_CR3,
VCPU_EXREG_CR4,
VCPU_EXREG_RFLAGS,
VCPU_EXREG_SEGMENTS,
VCPU_EXREG_EXIT_INFO_1,
Expand Down Expand Up @@ -1092,7 +1093,6 @@ struct kvm_x86_ops {
struct kvm_segment *var, int seg);
void (*get_cs_db_l_bits)(struct kvm_vcpu *vcpu, int *db, int *l);
void (*decache_cr0_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);
int (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
void (*set_efer)(struct kvm_vcpu *vcpu, u64 efer);
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5 changes: 3 additions & 2 deletions arch/x86/kvm/kvm_cache_regs.h
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Original file line number Diff line number Diff line change
Expand Up @@ -129,8 +129,9 @@ static inline ulong kvm_read_cr0(struct kvm_vcpu *vcpu)
static inline ulong kvm_read_cr4_bits(struct kvm_vcpu *vcpu, ulong mask)
{
ulong tmask = mask & KVM_POSSIBLE_CR4_GUEST_BITS;
if (tmask & vcpu->arch.cr4_guest_owned_bits)
kvm_x86_ops.decache_cr4_guest_bits(vcpu);
if ((tmask & vcpu->arch.cr4_guest_owned_bits) &&
!kvm_register_is_available(vcpu, VCPU_EXREG_CR4))
kvm_x86_ops.cache_reg(vcpu, VCPU_EXREG_CR4);
return vcpu->arch.cr4 & mask;
}

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5 changes: 0 additions & 5 deletions arch/x86/kvm/svm/svm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1525,10 +1525,6 @@ static void svm_decache_cr0_guest_bits(struct kvm_vcpu *vcpu)
{
}

static void svm_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
{
}

static void update_cr0_intercept(struct vcpu_svm *svm)
{
ulong gcr0 = svm->vcpu.arch.cr0;
Expand Down Expand Up @@ -4007,7 +4003,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
.get_cpl = svm_get_cpl,
.get_cs_db_l_bits = kvm_get_cs_db_l_bits,
.decache_cr0_guest_bits = svm_decache_cr0_guest_bits,
.decache_cr4_guest_bits = svm_decache_cr4_guest_bits,
.set_cr0 = svm_set_cr0,
.set_cr4 = svm_set_cr4,
.set_efer = svm_set_efer,
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18 changes: 9 additions & 9 deletions arch/x86/kvm/vmx/vmx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2204,6 +2204,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
{
unsigned long guest_owned_bits;

kvm_register_mark_available(vcpu, reg);

switch (reg) {
Expand All @@ -2221,6 +2223,12 @@ static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
if (enable_unrestricted_guest || (enable_ept && is_paging(vcpu)))
vcpu->arch.cr3 = vmcs_readl(GUEST_CR3);
break;
case VCPU_EXREG_CR4:
guest_owned_bits = vcpu->arch.cr4_guest_owned_bits;

vcpu->arch.cr4 &= ~guest_owned_bits;
vcpu->arch.cr4 |= vmcs_readl(GUEST_CR4) & guest_owned_bits;
break;
default:
WARN_ON_ONCE(1);
break;
Expand Down Expand Up @@ -2922,14 +2930,6 @@ static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu)
vcpu->arch.cr0 |= vmcs_readl(GUEST_CR0) & cr0_guest_owned_bits;
}

static void vmx_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
{
ulong cr4_guest_owned_bits = vcpu->arch.cr4_guest_owned_bits;

vcpu->arch.cr4 &= ~cr4_guest_owned_bits;
vcpu->arch.cr4 |= vmcs_readl(GUEST_CR4) & cr4_guest_owned_bits;
}

static void ept_load_pdptrs(struct kvm_vcpu *vcpu)
{
struct kvm_mmu *mmu = vcpu->arch.walk_mmu;
Expand Down Expand Up @@ -3128,6 +3128,7 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
return 1;

vcpu->arch.cr4 = cr4;
kvm_register_mark_available(vcpu, VCPU_EXREG_CR4);

if (!enable_unrestricted_guest) {
if (enable_ept) {
Expand Down Expand Up @@ -7809,7 +7810,6 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
.get_cpl = vmx_get_cpl,
.get_cs_db_l_bits = vmx_get_cs_db_l_bits,
.decache_cr0_guest_bits = vmx_decache_cr0_guest_bits,
.decache_cr4_guest_bits = vmx_decache_cr4_guest_bits,
.set_cr0 = vmx_set_cr0,
.set_cr4 = vmx_set_cr4,
.set_efer = vmx_set_efer,
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1 change: 1 addition & 0 deletions arch/x86/kvm/vmx/vmx.h
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Original file line number Diff line number Diff line change
Expand Up @@ -453,6 +453,7 @@ static inline void vmx_register_cache_reset(struct kvm_vcpu *vcpu)
| (1 << VCPU_EXREG_PDPTR)
| (1 << VCPU_EXREG_SEGMENTS)
| (1 << VCPU_EXREG_CR3)
| (1 << VCPU_EXREG_CR4)
| (1 << VCPU_EXREG_EXIT_INFO_1)
| (1 << VCPU_EXREG_EXIT_INFO_2));
vcpu->arch.regs_dirty = 0;
Expand Down

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