KVM: x86: Fix INIT signal handling in various CPU states

Commit cd7764fe9f73 ("KVM: x86: latch INITs while in system management mode")
changed code to latch INIT while vCPU is in SMM and process latched INIT
when leaving SMM. It left a subtle remark in commit message that similar
treatment should also be done while vCPU is in VMX non-root-mode.

However, INIT signals should actually be latched in various vCPU states:
(*) For both Intel and AMD, INIT signals should be latched while vCPU
is in SMM.
(*) For Intel, INIT should also be latched while vCPU is in VMX
operation and later processed when vCPU leaves VMX operation by
executing VMXOFF.
(*) For AMD, INIT should also be latched while vCPU runs with GIF=0
or in guest-mode with intercept defined on INIT signal.

To fix this:
1) Add kvm_x86_ops->apic_init_signal_blocked() such that each CPU vendor
can define the various CPU states in which INIT signals should be
blocked and modify kvm_apic_accept_events() to use it.
2) Modify vmx_check_nested_events() to check for pending INIT signal
while vCPU in guest-mode. If so, emualte vmexit on
EXIT_REASON_INIT_SIGNAL. Note that nSVM should have similar behaviour
but is currently left as a TODO comment to implement in the future
because nSVM don't yet implement svm_check_nested_events().

Note: Currently KVM nVMX implementation don't support VMX wait-for-SIPI
activity state as specified in MSR_IA32_VMX_MISC bits 6:8 exposed to
guest (See nested_vmx_setup_ctls_msrs()).
If and when support for this activity state will be implemented,
kvm_check_nested_events() would need to avoid emulating vmexit on
INIT signal in case activity-state is wait-for-SIPI. In addition,
kvm_apic_accept_events() would need to be modified to avoid discarding
SIPI in case VMX activity-state is wait-for-SIPI but instead delay
SIPI processing to vmx_check_nested_events() that would clear
pending APIC events and emulate vmexit on SIPI.

Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Co-developed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Signed-off-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 2854aafc489e..d24050b647c7 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -7170,6 +7170,21 @@ static bool svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
 	return false;
 }
 
+static bool svm_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	/*
+	 * TODO: Last condition latch INIT signals on vCPU when
+	 * vCPU is in guest-mode and vmcb12 defines intercept on INIT.
+	 * To properly emulate the INIT intercept, SVM should implement
+	 * kvm_x86_ops->check_nested_events() and call nested_svm_vmexit()
+	 * there if an INIT signal is pending.
+	 */
+	return !gif_set(svm) ||
+		   (svm->vmcb->control.intercept & (1ULL << INTERCEPT_INIT));
+}
+
 static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
 	.cpu_has_kvm_support = has_svm,
 	.disabled_by_bios = is_disabled,
@@ -7306,6 +7321,8 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
 	.nested_get_evmcs_version = nested_get_evmcs_version,
 
 	.need_emulation_on_page_fault = svm_need_emulation_on_page_fault,
+
+	.apic_init_signal_blocked = svm_apic_init_signal_blocked,
 };
 
 static int __init svm_init(void)