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KVM: nVMX: Always write vmcs02.GUEST_CR3 during nested VM-Enter

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Write the desired L2 CR3 into vmcs02.GUEST_CR3 during nested VM-Enter
instead of deferring the VMWRITE until vmx_set_cr3().  If the VMWRITE
is deferred, then KVM can consume a stale vmcs02.GUEST_CR3 when it
refreshes vmcs12->guest_cr3 during nested_vmx_vmexit() if the emulated
VM-Exit occurs without actually entering L2, e.g. if the nested run
is squashed because nested VM-Enter (from L1) is putting L2 into HLT.

Note, the above scenario can occur regardless of whether L1 is
intercepting HLT, e.g. L1 can intercept HLT and then re-enter L2 with
vmcs.GUEST_ACTIVITY_STATE=HALTED.  But practically speaking, a VMM will
likely put a guest into HALTED if and only if it's not intercepting HLT.

In an ideal world where EPT *requires* unrestricted guest (and vice
versa), VMX could handle CR3 similar to how it handles RSP and RIP,
e.g. mark CR3 dirty and conditionally load it at vmx_vcpu_run().  But
the unrestricted guest silliness complicates the dirty tracking logic
to the point that explicitly handling vmcs02.GUEST_CR3 during nested
VM-Enter is a simpler overall implementation.

Cc: stable@vger.kernel.org
Reported-and-tested-by: Reto Buerki <reet@codelabs.ch>
Tested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2019-09-27 14:45:16 -07:00 committed by Paolo Bonzini
parent 83af5e65a8
commit 04f11ef458
2 changed files with 17 additions and 3 deletions
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10
arch/x86/kvm/vmx/nested.c
View File

@ -2418,6 +2418,16 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
entry_failure_code))
return -EINVAL;
/*
* Immediately write vmcs02.GUEST_CR3. It will be propagated to vmcs12
* on nested VM-Exit, which can occur without actually running L2 and
* thus without hitting vmx_set_cr3(), e.g. if L1 is entering L2 with
* vmcs12.GUEST_ACTIVITYSTATE=HLT, in which case KVM will intercept the
* transition to HLT instead of running L2.
*/
if (enable_ept)
vmcs_writel(GUEST_CR3, vmcs12->guest_cr3);
/* Late preparation of GUEST_PDPTRs now that EFER and CRs are set. */
if (load_guest_pdptrs_vmcs12 && nested_cpu_has_ept(vmcs12) &&
is_pae_paging(vcpu)) {

10
arch/x86/kvm/vmx/vmx.c
View File

@ -2989,6 +2989,7 @@ u64 construct_eptp(struct kvm_vcpu *vcpu, unsigned long root_hpa)
void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
{
struct kvm *kvm = vcpu->kvm;
bool update_guest_cr3 = true;
unsigned long guest_cr3;
u64 eptp;
@ -3005,15 +3006,18 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
}
if (enable_unrestricted_guest || is_paging(vcpu) ||
is_guest_mode(vcpu))
/* Loading vmcs02.GUEST_CR3 is handled by nested VM-Enter. */
if (is_guest_mode(vcpu))
update_guest_cr3 = false;
else if (enable_unrestricted_guest || is_paging(vcpu))
guest_cr3 = kvm_read_cr3(vcpu);
else
guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr;
ept_load_pdptrs(vcpu);
}
vmcs_writel(GUEST_CR3, guest_cr3);
if (update_guest_cr3)
vmcs_writel(GUEST_CR3, guest_cr3);
}
int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)