[PATCH 2/7] KVM: x86: inhibit APICv/AVIC when the guest and/or host changes either apic id or the apic base from their default values.

Maxim Levitsky
2022-06-06T18:09:03Z

Neither of these settings should be changed by the guest and it is
a burden to support it in the acceleration code, so just inhibit
this code instead.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 9 +++++++++
arch/x86/kvm/lapic.c | 27 +++++++++++++++++++++++----
arch/x86/kvm/svm/avic.c | 4 +++-
arch/x86/kvm/vmx/vmx.c | 4 +++-
4 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d7fb3ade44501..971db02e8ed86 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1094,6 +1094,15 @@ enum kvm_apicv_inhibit {
*/
APICV_INHIBIT_REASON_BLOCKIRQ,

+ /*
+ * For simplicity, the APIC acceleration is inhibited
+ * first time either APIC ID or APIC base are changed by the guest
+ * from their reset values.
+ */
+ APICV_INHIBIT_REASON_APIC_ID_MODIFIED,
+ APICV_INHIBIT_REASON_APIC_BASE_MODIFIED,
+
+
/******************************************************/
/* INHIBITs that are relevant only to the AMD's AVIC. */
/******************************************************/
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e69b83708f050..a413a1d8df4c1 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2040,6 +2040,19 @@ static void apic_manage_nmi_watchdog(struct kvm_lapic *apic, u32 lvt0_val)
}
}

+static void kvm_lapic_xapic_id_updated(struct kvm_lapic *apic)
+{
+ struct kvm *kvm = apic->vcpu->kvm;
+
+ if (KVM_BUG_ON(apic_x2apic_mode(apic), kvm))
+ return;
+
+ if (kvm_xapic_id(apic) == apic->vcpu->vcpu_id)
+ return;
+
+ kvm_set_apicv_inhibit(apic->vcpu->kvm, APICV_INHIBIT_REASON_APIC_ID_MODIFIED);
+}
+
static int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
{
int ret = 0;
@@ -2048,10 +2061,12 @@ static int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)

switch (reg) {
case APIC_ID: /* Local APIC ID */
- if (!apic_x2apic_mode(apic))
+ if (!apic_x2apic_mode(apic)) {
kvm_apic_set_xapic_id(apic, val >> 24);
- else
+ kvm_lapic_xapic_id_updated(apic);
+ } else {
ret = 1;
+ }
break;

case APIC_TASKPRI:
@@ -2354,8 +2369,10 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
MSR_IA32_APICBASE_BASE;

if ((value & MSR_IA32_APICBASE_ENABLE) &&
- apic->base_address != APIC_DEFAULT_PHYS_BASE)
- pr_warn_once("APIC base relocation is unsupported by KVM");
+ apic->base_address != APIC_DEFAULT_PHYS_BASE) {
+ kvm_set_apicv_inhibit(apic->vcpu->kvm,
+ APICV_INHIBIT_REASON_APIC_BASE_MODIFIED);
+ }
}

void kvm_apic_update_apicv(struct kvm_vcpu *vcpu)
@@ -2666,6 +2683,8 @@ static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
icr = __kvm_lapic_get_reg64(s->regs, APIC_ICR);
__kvm_lapic_set_reg(s->regs, APIC_ICR2, icr >> 32);
}
+ } else {
+ kvm_lapic_xapic_id_updated(vcpu->arch.apic);
}

return 0;
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 54fe03714f8a6..8dffd67f60862 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -910,7 +910,9 @@ bool avic_check_apicv_inhibit_reasons(enum kvm_apicv_inhibit reason)
BIT(APICV_INHIBIT_REASON_PIT_REINJ) |
BIT(APICV_INHIBIT_REASON_X2APIC) |
BIT(APICV_INHIBIT_REASON_BLOCKIRQ) |
- BIT(APICV_INHIBIT_REASON_SEV);
+ BIT(APICV_INHIBIT_REASON_SEV |
+ BIT(APICV_INHIBIT_REASON_APIC_ID_MODIFIED) |
+ BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED));

return supported & BIT(reason);
}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fd2e707faf2bf..48440f73c3352 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7860,7 +7860,9 @@ static bool vmx_check_apicv_inhibit_reasons(enum kvm_apicv_inhibit reason)
ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
BIT(APICV_INHIBIT_REASON_ABSENT) |
BIT(APICV_INHIBIT_REASON_HYPERV) |
- BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
+ BIT(APICV_INHIBIT_REASON_BLOCKIRQ) |
+ BIT(APICV_INHIBIT_REASON_APIC_ID_MODIFIED) |
+ BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED);

return supported & BIT(reason);
}
--
2.26.3