linux-kernel - [PATCH RESEND 4/5] x86/kvm: Add MSR_KVM_PREEMPT

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Message-Id: <1648216709-44755-5-git-send-email-wanpengli@tencent.com>
Date:   Fri, 25 Mar 2022 06:58:28 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH RESEND 4/5] x86/kvm: Add MSR_KVM_PREEMPT_COUNT guest support

From: Wanpeng Li <wanpengli@...cent.com>

The x86 guest passes the per-cpu preempt_count value to the hypervisor,
so the hypervisor knows whether the guest is running in the critical 
section.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kernel/kvm.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 21933095a10e..e389fa4393ae 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -366,6 +366,14 @@ static void kvm_guest_cpu_init(void)
 
 	if (has_steal_clock)
 		kvm_register_steal_time();
+
+	if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_COUNT)) {
+		u64 pa = slow_virt_to_phys(this_cpu_ptr(&__preempt_count))
+			| KVM_MSR_ENABLED;
+		wrmsrl(MSR_KVM_PREEMPT_COUNT, pa);
+
+		pr_debug("setup pv preempt_count: cpu %d\n", smp_processor_id());
+	}
 }
 
 static void kvm_pv_disable_apf(void)
@@ -442,6 +450,8 @@ static void kvm_guest_cpu_offline(bool shutdown)
 	if (!shutdown)
 		apf_task_wake_all();
 	kvmclock_disable();
+	if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_COUNT))
+		wrmsrl(MSR_KVM_PREEMPT_COUNT, 0);
 }
 
 static int kvm_cpu_online(unsigned int cpu)
-- 
2.25.1