From: Sean Christopherson <seanjc@google.com>
Date: Fri, 19 Sep 2025 00:59:48 +0000 (-0700)
Subject: KVM: nVMX: Hardcode dummy EPTP used for early nested consistency checks
X-Git-Tag: v6.19-rc1~103^2~5^2~9
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a8749281e4c63e582574ae4409be7641763e58ad;p=thirdparty%2Flinux.git

KVM: nVMX: Hardcode dummy EPTP used for early nested consistency checks

Hardcode the dummy EPTP used for "early" consistency checks as there's no
need to use 5-level EPT based on the guest.MAXPHYADDR (the EPTP just needs
to be valid, it's never truly consumed).

This will allow breaking construct_eptp()'s dependency on having access to
the vCPU, which in turn will (much further in the future) allow for eliding
per-root TLB flushes when a vCPU is migrated between pCPUs (a flush is
need if and only if that particular pCPU hasn't already flushed the vCPU's
roots).

Link: https://lore.kernel.org/r/20250919005955.1366256-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 3fca63a261f5e..0a4b4e790f9f0 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2297,13 +2297,11 @@ static void prepare_vmcs02_constant_state(struct vcpu_vmx *vmx)
 	vmx->nested.vmcs02_initialized = true;
 
 	/*
-	 * We don't care what the EPTP value is we just need to guarantee
-	 * it's valid so we don't get a false positive when doing early
-	 * consistency checks.
+	 * If early consistency checks are enabled, stuff the EPT Pointer with
+	 * a dummy *legal* value to avoid false positives on bad control state.
 	 */
 	if (enable_ept && nested_early_check)
-		vmcs_write64(EPT_POINTER,
-			     construct_eptp(&vmx->vcpu, 0, PT64_ROOT_4LEVEL));
+		vmcs_write64(EPT_POINTER, VMX_EPTP_MT_WB | VMX_EPTP_PWL_4);
 
 	if (vmx->ve_info)
 		vmcs_write64(VE_INFORMATION_ADDRESS, __pa(vmx->ve_info));
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 98506c7232913..6a1377015a2a6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3219,7 +3219,7 @@ static inline int vmx_get_current_vpid(struct kvm_vcpu *vcpu)
 	return to_vmx(vcpu)->vpid;
 }
 
-u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level)
+static u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level)
 {
 	u64 eptp = VMX_EPTP_MT_WB;
 
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index ea93121029f91..6cb04a6afeefb 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -369,7 +369,6 @@ void set_cr4_guest_host_mask(struct vcpu_vmx *vmx);
 void ept_save_pdptrs(struct kvm_vcpu *vcpu);
 void vmx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
 void __vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
-u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level);
 
 bool vmx_guest_inject_ac(struct kvm_vcpu *vcpu);
 void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu);