[PATCH 08/15] KVM: nVMX: Don't speculatively write virtual-APIC page address

Sean Christopherson
2019-05-07T16:07:02Z

The VIRTUAL_APIC_PAGE_ADDR in vmcs02 is guaranteed to be updated before
it is consumed by hardware, either in nested_vmx_enter_non_root_mode()
or via the KVM_REQ_GET_VMCS12_PAGES callback. Avoid an extra VMWRITE
and only stuff a bad value into vmcs02 when mapping vmcs12's address
fails. This also eliminates the need for extra comments to connect the
dots between prepare_vmcs02_early() and nested_get_vmcs12_pages().

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/vmx/nested.c | 21 ++++++++-------------
1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 99164d054922..32d233dee067 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2038,20 +2038,13 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
exec_control &= ~CPU_BASED_TPR_SHADOW;
exec_control |= vmcs12->cpu_based_vm_exec_control;

- /*
- * Write an illegal value to VIRTUAL_APIC_PAGE_ADDR. Later, if
- * nested_get_vmcs12_pages can't fix it up, the illegal value
- * will result in a VM entry failure.
- */
- if (exec_control & CPU_BASED_TPR_SHADOW) {
- vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, -1ull);
+ if (exec_control & CPU_BASED_TPR_SHADOW)
vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);
- } else {
#ifdef CONFIG_X86_64
+ else
exec_control |= CPU_BASED_CR8_LOAD_EXITING |
CPU_BASED_CR8_STORE_EXITING;
#endif
- }

/*
* A vmexit (to either L1 hypervisor or L0 userspace) is always needed
@@ -2869,10 +2862,6 @@ static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
if (nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW)) {
map = &vmx->nested.virtual_apic_map;

- /*
- * If translation failed, VM entry will fail because
- * prepare_vmcs02 set VIRTUAL_APIC_PAGE_ADDR to -1ull.
- */
if (!kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->virtual_apic_page_addr), map)) {
vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, pfn_to_hpa(map->pfn));
} else if (nested_cpu_has(vmcs12, CPU_BASED_CR8_LOAD_EXITING) &&
@@ -2888,6 +2877,12 @@ static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
*/
vmcs_clear_bits(CPU_BASED_VM_EXEC_CONTROL,
CPU_BASED_TPR_SHADOW);
+ } else {
+ /*
+ * Write an illegal value to VIRTUAL_APIC_PAGE_ADDR to
+ * force VM-Entry to fail.
+ */
+ vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, -1ull);
}
}

--
2.21.0