kvm: i8254: Deactivate APICv when using in-kernel PIT re-injection mode.

AMD SVM AVIC accelerates EOI write and does not trap. This causes
in-kernel PIT re-injection mode to fail since it relies on irq-ack
notifier mechanism. So, APICv is activated only when in-kernel PIT
is in discard mode e.g. w/ qemu option:

  -global kvm-pit.lost_tick_policy=discard

Also, introduce APICV_INHIBIT_REASON_PIT_REINJ bit to be used for this
reason.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2bd7fd9..4dffbc1 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -879,6 +879,7 @@ enum kvm_irqchip_mode {
 #define APICV_INHIBIT_REASON_HYPERV     1
 #define APICV_INHIBIT_REASON_NESTED     2
 #define APICV_INHIBIT_REASON_IRQWIN     3
+#define APICV_INHIBIT_REASON_PIT_REINJ  4
 
 struct kvm_arch {
        unsigned long n_used_mmu_pages;

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 4a6dc54..b24c606 100644 (file)
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -295,12 +295,24 @@ void kvm_pit_set_reinject(struct kvm_pit *pit, bool reinject)
        if (atomic_read(&ps->reinject) == reinject)
                return;
 
+       /*
+        * AMD SVM AVIC accelerates EOI write and does not trap.
+        * This cause in-kernel PIT re-inject mode to fail
+        * since it checks ps->irq_ack before kvm_set_irq()
+        * and relies on the ack notifier to timely queue
+        * the pt->worker work iterm and reinject the missed tick.
+        * So, deactivate APICv when PIT is in reinject mode.
+        */
        if (reinject) {
+               kvm_request_apicv_update(kvm, false,
+                                        APICV_INHIBIT_REASON_PIT_REINJ);
                /* The initial state is preserved while ps->reinject == 0. */
                kvm_pit_reset_reinject(pit);
                kvm_register_irq_ack_notifier(kvm, &ps->irq_ack_notifier);
                kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
        } else {
+               kvm_request_apicv_update(kvm, true,
+                                        APICV_INHIBIT_REASON_PIT_REINJ);
                kvm_unregister_irq_ack_notifier(kvm, &ps->irq_ack_notifier);
                kvm_unregister_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
        }

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 6d300c1..0b05967 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1739,7 +1739,13 @@ static int avic_update_access_page(struct kvm *kvm, bool activate)
        int ret = 0;
 
        mutex_lock(&kvm->slots_lock);
-       if (kvm->arch.apic_access_page_done == activate)
+       /*
+        * During kvm_destroy_vm(), kvm_pit_set_reinject() could trigger
+        * APICv mode change, which update APIC_ACCESS_PAGE_PRIVATE_MEMSLOT
+        * memory region. So, we need to ensure that kvm->mm == current->mm.
+        */
+       if ((kvm->arch.apic_access_page_done == activate) ||
+           (kvm->mm != current->mm))
                goto out;
 
        ret = __x86_set_memory_region(kvm,
@@ -7353,7 +7359,8 @@ static bool svm_check_apicv_inhibit_reasons(ulong bit)
        ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
                          BIT(APICV_INHIBIT_REASON_HYPERV) |
                          BIT(APICV_INHIBIT_REASON_NESTED) |
-                         BIT(APICV_INHIBIT_REASON_IRQWIN);
+                         BIT(APICV_INHIBIT_REASON_IRQWIN) |
+                         BIT(APICV_INHIBIT_REASON_PIT_REINJ);
 
        return supported & BIT(bit);
 }