[PATCH v3 4/7] KVM: VMX: Handle vectoring error in check_emulate_instruction

[Ivan Orlov <iorlov@amazon.com>]

Move unhandleable vmexit during vectoring error detection
into check_emulate_instruction. Implement the function which prohibits
the emulation if EMULTYPE_PF is set when vectoring, otherwise such a
situation may occur:

1. CPU executes an instruction and hits a #GP
2. While vectoring the #GP, a shadow #PF occurs
3. On vmexit, KVM re-injects #GP
4. KVM emulates because of the write-protected page
5. KVM "successfully" emulates and also detects the #GP
6. KVM synthesizes a #GP, and since #GP has already been injected,
incorrectly escalates to a #DF.

Fix the comment about EMULTYPE_PF as this flag doesn't necessarily
mean MMIO anymore: it can also be set due to the write protection
violation.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Ivan Orlov <iorlov@amazon.com>
---
V1 -> V2:
- Detect the unhandleable vectoring error in vmx_check_emulate_instruction
instead of handling it in the common MMU code (which is specific for
cached MMIO)
V2 -> V3:
- Prohibit any emulation during vectoring if it happens due to an
intercepted #PF.

 arch/x86/include/asm/kvm_host.h |  9 +++++++--
 arch/x86/kvm/vmx/vmx.c          | 23 +++++++++--------------
 2 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index de8fb1ab230c..f3a1d050e1d6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2019,8 +2019,8 @@ u64 vcpu_tsc_khz(struct kvm_vcpu *vcpu);
  *			VMware backdoor emulation handles select instructions
  *			and reinjects the #GP for all other cases.
  *
- * EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, in which
- *		 case the CR2/GPA value pass on the stack is valid.
+ * EMULTYPE_PF - Set when an intercepted #PF triggers the emulation, in which case
+ *		 the CR2/GPA value pass on the stack is valid.
  *
  * EMULTYPE_COMPLETE_USER_EXIT - Set when the emulator should update interruptibility
  *				 state and inject single-step #DBs after skipping
@@ -2055,6 +2055,11 @@ u64 vcpu_tsc_khz(struct kvm_vcpu *vcpu);
 #define EMULTYPE_COMPLETE_USER_EXIT (1 << 7)
 #define EMULTYPE_WRITE_PF_TO_SP	    (1 << 8)
 
+static inline bool kvm_can_emulate_event_vectoring(int emul_type)
+{
+	return !(emul_type & EMULTYPE_PF);
+}
+
 int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
 int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
 					void *insn, int insn_len);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index acc2f0e0a339..89ddbe1175c7 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1705,6 +1705,12 @@ int vmx_check_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
 		kvm_queue_exception(vcpu, UD_VECTOR);
 		return X86EMUL_PROPAGATE_FAULT;
 	}
+
+	/* Check that emulation is possible during event vectoring */
+	if ((to_vmx(vcpu)->idt_vectoring_info & VECTORING_INFO_VALID_MASK) &&
+	    !kvm_can_emulate_event_vectoring(emul_type))
+		return X86EMUL_UNHANDLEABLE_VECTORING;
+
 	return X86EMUL_CONTINUE;
 }
 
@@ -6543,26 +6549,15 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
 		return 0;
 	}
 
-	/*
-	 * Note:
-	 * Do not try to fix EXIT_REASON_EPT_MISCONFIG if it caused by
-	 * delivery event since it indicates guest is accessing MMIO.
-	 * The vm-exit can be triggered again after return to guest that
-	 * will cause infinite loop.
-	 */
 	if ((vectoring_info & VECTORING_INFO_VALID_MASK) &&
 	    (exit_reason.basic != EXIT_REASON_EXCEPTION_NMI &&
 	     exit_reason.basic != EXIT_REASON_EPT_VIOLATION &&
 	     exit_reason.basic != EXIT_REASON_PML_FULL &&
 	     exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
 	     exit_reason.basic != EXIT_REASON_TASK_SWITCH &&
-	     exit_reason.basic != EXIT_REASON_NOTIFY)) {
-		gpa_t gpa = INVALID_GPA;
-
-		if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG)
-			gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
-
-		kvm_prepare_event_vectoring_exit(vcpu, gpa);
+	     exit_reason.basic != EXIT_REASON_NOTIFY &&
+	     exit_reason.basic != EXIT_REASON_EPT_MISCONFIG)) {
+		kvm_prepare_event_vectoring_exit(vcpu, INVALID_GPA);
 		return 0;
 	}
 
-- 
2.43.0