[PATCH v4 13/17] kvm: i8254: Deactivate APICv when using in-kernel PIT re-injection mode.

From: "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Cc: "pbonzini@redhat.com" <pbonzini@redhat.com>,
	"rkrcmar@redhat.com" <rkrcmar@redhat.com>,
	"joro@8bytes.org" <joro@8bytes.org>,
	"vkuznets@redhat.com" <vkuznets@redhat.com>,
	"rkagan@virtuozzo.com" <rkagan@virtuozzo.com>,
	"graf@amazon.com" <graf@amazon.com>,
	"jschoenh@amazon.de" <jschoenh@amazon.de>,
	"karahmed@amazon.de" <karahmed@amazon.de>,
	"rimasluk@amazon.com" <rimasluk@amazon.com>,
	"Grimm, Jon" <Jon.Grimm@amd.com>,
	"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com>
Subject: [PATCH v4 13/17] kvm: i8254: Deactivate APICv when using in-kernel PIT re-injection mode.
Date: Fri, 1 Nov 2019 22:41:37 +0000	[thread overview]
Message-ID: <1572648072-84536-14-git-send-email-suravee.suthikulpanit@amd.com> (raw)
In-Reply-To: <1572648072-84536-1-git-send-email-suravee.suthikulpanit@amd.com>

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

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/i8254.c            | 10 ++++++++++
 arch/x86/kvm/svm.c              |  8 +++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index fe61269..460f7a4 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -858,6 +858,7 @@ enum kvm_irqchip_mode {
 #define APICV_DEACT_BIT_HYPERV     1
 #define APICV_DEACT_BIT_NESTED     2
 #define APICV_DEACT_BIT_IRQWIN     3
+#define APICV_DEACT_BIT_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..3f77fda 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -295,12 +295,22 @@ 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_DEACT_BIT_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_DEACT_BIT_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 0e7ff04..9812feb 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1679,7 +1679,13 @@ 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,
-- 
1.8.3.1

