Re: [PATCH 07/12] KVM: nVMX: Disable vmcs02 posted interrupts if vmcs12 PID isn't mappable
From: Sean Christopherson <seanjc@google.com>
Date: 2021-05-24 23:22:04
On Thu, May 20, 2021, Jim Mattson wrote:
quoted hunk ↗ jump to hunk
Don't allow posted interrupts to modify a stale posted interrupt descriptor (including the initial value of 0). Empirical tests on real hardware reveal that a posted interrupt descriptor referencing an unbacked address has PCI bus error semantics (reads as all 1's; writes are ignored). However, kvm can't distinguish unbacked addresses from device-backed (MMIO) addresses, so it should really ask userspace for an MMIO completion. That's overly complicated, so just punt with KVM_INTERNAL_ERROR. Don't return the error until the posted interrupt descriptor is actually accessed. We don't want to break the existing kvm-unit-tests that assume they can launch an L2 VM with a posted interrupt descriptor that references MMIO space in L1. Fixes: 6beb7bd52e48 ("kvm: nVMX: Refactor nested_get_vmcs12_pages()") Signed-off-by: Jim Mattson <redacted> --- arch/x86/kvm/vmx/nested.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 706c31821362..defd42201bb4 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c@@ -3175,6 +3175,15 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu) offset_in_page(vmcs12->posted_intr_desc_addr)); vmcs_write64(POSTED_INTR_DESC_ADDR, pfn_to_hpa(map->pfn) + offset_in_page(vmcs12->posted_intr_desc_addr)); + } else { + /* + * Defer the KVM_INTERNAL_ERROR exit until + * someone tries to trigger posted interrupt + * processing on this vCPU, to avoid breaking + * existing kvm-unit-tests.
Run the lines out to 80 chars. Also, can we change the comment to tie it to CPU behavior in someway? A few years down the road, "existing kvm-unit-tests" may not have any relevant meaning, and it's not like kvm-unit-tests is bug free either. E.g. something like /* * Defer the KVM_INTERNAL_ERROR exit until posted * interrupt processing actually occurs on this vCPU. * Until that happens, the descriptor is not accessed, * and userspace can technically rely on that behavior. */
quoted hunk ↗ jump to hunk
+ */ + vmx->nested.pi_desc = NULL; + pin_controls_clearbit(vmx, PIN_BASED_POSTED_INTR); } } if (nested_vmx_prepare_msr_bitmap(vcpu, vmcs12))@@ -3689,10 +3698,14 @@ static int vmx_complete_nested_posted_interrupt(struct kvm_vcpu *vcpu) void *vapic_page; u16 status; - if (!vmx->nested.pi_desc || !vmx->nested.pi_pending) + if (!vmx->nested.pi_pending) return 0; + if (!vmx->nested.pi_desc) + goto mmio_needed; + vmx->nested.pi_pending = false; + if (!pi_test_and_clear_on(vmx->nested.pi_desc)) return 0;-- 2.31.1.818.g46aad6cb9e-goog