diff options
| author | Sean Christopherson <sean.j.christopherson@intel.com> | 2020-05-01 21:32:26 -0700 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-05-13 12:15:09 -0400 |
| commit | 0cc69204e77275105d5b0fc4cf3c970e3579457f (patch) | |
| tree | 5ad3687e736e7797d5483d9caf296eeff4bce377 /arch | |
| parent | 56ba77a459a72a7d95be74355a40a91e1f6dd7f7 (diff) | |
KVM: nVMX: Unconditionally validate CR3 during nested transitions
Unconditionally check the validity of the incoming CR3 during nested
VM-Enter/VM-Exit to avoid invoking kvm_read_cr3() in the common case
where the guest isn't using PAE paging. If vmcs.GUEST_CR3 hasn't yet
been cached (common case), kvm_read_cr3() will trigger a VMREAD. The
VMREAD (~30 cycles) alone is likely slower than nested_cr3_valid()
(~5 cycles if vcpu->arch.maxphyaddr gets a cache hit), and the poor
exchange only gets worse when retpolines are enabled as the call to
kvm_x86_ops.cache_reg() will incur a retpoline (60+ cycles).
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200502043234.12481-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/vmx/nested.c | 27 |
1 files changed, 13 insertions, 14 deletions
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index b69f5a2fa362..90ba278dd572 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -1119,21 +1119,20 @@ static bool nested_vmx_transition_mmu_sync(struct kvm_vcpu *vcpu) static int nested_vmx_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3, bool nested_ept, u32 *entry_failure_code) { - if (cr3 != kvm_read_cr3(vcpu) || (!nested_ept && pdptrs_changed(vcpu))) { - if (CC(!nested_cr3_valid(vcpu, cr3))) { - *entry_failure_code = ENTRY_FAIL_DEFAULT; - return -EINVAL; - } + if (CC(!nested_cr3_valid(vcpu, cr3))) { + *entry_failure_code = ENTRY_FAIL_DEFAULT; + return -EINVAL; + } - /* - * If PAE paging and EPT are both on, CR3 is not used by the CPU and - * must not be dereferenced. - */ - if (is_pae_paging(vcpu) && !nested_ept) { - if (CC(!load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))) { - *entry_failure_code = ENTRY_FAIL_PDPTE; - return -EINVAL; - } + /* + * If PAE paging and EPT are both on, CR3 is not used by the CPU and + * must not be dereferenced. + */ + if (!nested_ept && is_pae_paging(vcpu) && + (cr3 != kvm_read_cr3(vcpu) || pdptrs_changed(vcpu))) { + if (CC(!load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))) { + *entry_failure_code = ENTRY_FAIL_PDPTE; + return -EINVAL; } } |