KVM: VMX: Add proper cache tracking for CR4

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>

arch/x86/include/asm/kvm_host.h

@@ -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,
@@ -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);

arch/x86/kvm/kvm_cache_regs.h

@@ -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)
+	if ((tmask & vcpu->arch.cr4_guest_owned_bits) &&
-		kvm_x86_ops.decache_cr4_guest_bits(vcpu);
+	    !kvm_register_is_available(vcpu, VCPU_EXREG_CR4))
+		kvm_x86_ops.cache_reg(vcpu, VCPU_EXREG_CR4);
 	return vcpu->arch.cr4 & mask;
 }
 

arch/x86/kvm/svm/svm.c

@@ -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;
@@ -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,

arch/x86/kvm/vmx/vmx.c

@@ -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) {
@@ -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;
@@ -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;
@@ -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) {
@@ -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,

arch/x86/kvm/vmx/vmx.h

@@ -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;