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

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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>
This commit is contained in:
Sean Christopherson 2025-09-18 17:59:48 -07:00
parent f48888bb8a
commit a8749281e4
3 changed files with 4 additions and 7 deletions
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8
arch/x86/kvm/vmx/nested.c
View File

@ -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));

2
arch/x86/kvm/vmx/vmx.c
View File

@ -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;

1
arch/x86/kvm/vmx/vmx.h
View File

@ -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);