kvm: nVMX: support EPT accessed/dirty bits

Now use bit 6 of EPTP to optionally enable A/D bits for EPTP.  Another
thing to change is that, when EPT accessed and dirty bits are not in use,
VMX treats accesses to guest paging structures as data reads.  When they
are in use (bit 6 of EPTP is set), they are treated as writes and the
corresponding EPT dirty bit is set.  The MMU didn't know this detail,
so this patch adds it.

We also have to fix up the exit qualification.  It may be wrong because
KVM sets bit 6 but the guest might not.

L1 emulates EPT A/D bits using write permissions, so in principle it may
be possible for EPT A/D bits to be used by L1 even though not available
in hardware.  The problem is that guest page-table walks will be treated
as reads rather than writes, so they would not cause an EPT violation.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[Fixed typo in walk_addr_generic() comment and changed bit clear +
 conditional-set pattern in handle_ept_violation() to conditional-clear]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

1 files changed, 28 insertions, 4 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1c372600a962..5556cce99749 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2767,6 +2767,8 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
 		vmx->nested.nested_vmx_ept_caps |= VMX_EPT_EXTENT_GLOBAL_BIT |
 			VMX_EPT_EXTENT_CONTEXT_BIT | VMX_EPT_2MB_PAGE_BIT |
 			VMX_EPT_1GB_PAGE_BIT;
+	       if (enable_ept_ad_bits)
+		       vmx->nested.nested_vmx_ept_caps |= VMX_EPT_AD_BIT;
 	} else
 		vmx->nested.nested_vmx_ept_caps = 0;
 
@@ -6211,6 +6213,17 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 
 	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 
+	if (is_guest_mode(vcpu)
+	    && !(exit_qualification & EPT_VIOLATION_GVA_TRANSLATED)) {
+		/*
+		 * Fix up exit_qualification according to whether guest
+		 * page table accesses are reads or writes.
+		 */
+		u64 eptp = nested_ept_get_cr3(vcpu);
+		if (eptp & VMX_EPT_AD_ENABLE_BIT)
+			exit_qualification &= ~EPT_VIOLATION_ACC_WRITE;
+	}
+
 	/*
 	 * EPT violation happened while executing iret from NMI,
 	 * "blocked by NMI" bit has to be set before next VM entry.
@@ -9416,17 +9429,26 @@ static unsigned long nested_ept_get_cr3(struct kvm_vcpu *vcpu)
 	return get_vmcs12(vcpu)->ept_pointer;
 }
 
-static void nested_ept_init_mmu_context(struct kvm_vcpu *vcpu)
+static int nested_ept_init_mmu_context(struct kvm_vcpu *vcpu)
 {
+	u64 eptp;
+
 	WARN_ON(mmu_is_nested(vcpu));
+	eptp = nested_ept_get_cr3(vcpu);
+	if ((eptp & VMX_EPT_AD_ENABLE_BIT) && !enable_ept_ad_bits)
+		return 1;
+
+	kvm_mmu_unload(vcpu);
 	kvm_init_shadow_ept_mmu(vcpu,
 			to_vmx(vcpu)->nested.nested_vmx_ept_caps &
-			VMX_EPT_EXECUTE_ONLY_BIT);
+			VMX_EPT_EXECUTE_ONLY_BIT,
+			eptp & VMX_EPT_AD_ENABLE_BIT);
 	vcpu->arch.mmu.set_cr3           = vmx_set_cr3;
 	vcpu->arch.mmu.get_cr3           = nested_ept_get_cr3;
 	vcpu->arch.mmu.inject_page_fault = nested_ept_inject_page_fault;
 
 	vcpu->arch.walk_mmu              = &vcpu->arch.nested_mmu;
+	return 0;
 }
 
 static void nested_ept_uninit_mmu_context(struct kvm_vcpu *vcpu)
@@ -10188,8 +10210,10 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 	}
 
 	if (nested_cpu_has_ept(vmcs12)) {
-		kvm_mmu_unload(vcpu);
-		nested_ept_init_mmu_context(vcpu);
+		if (nested_ept_init_mmu_context(vcpu)) {
+			*entry_failure_code = ENTRY_FAIL_DEFAULT;
+			return 1;
+		}
 	} else if (nested_cpu_has2(vmcs12,
 				   SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
 		vmx_flush_tlb_ept_only(vcpu);