Commit a8749281 authored by Sean Christopherson's avatar Sean Christopherson
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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: default avatarSean Christopherson <seanjc@google.com>
parent f48888bb

arch/x86/kvm/vmx/nested.c

+3 −5
Original line number Diff line number Diff line
@@ -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));

arch/x86/kvm/vmx/vmx.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

arch/x86/kvm/vmx/vmx.h

+0 −1
Original line number Diff line number Diff line
@@ -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);