From 77bcd9e6231a5297ef417a7d7f734d61c2bcceb6 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Tue, 9 Jan 2024 16:39:35 -0800
Subject: [PATCH] KVM: Add dedicated arch hook for querying if vCPU was
preempted in-kernel
Plumb in a dedicated hook for querying whether or not a vCPU was preempted
in-kernel. Unlike literally every other architecture, x86's VMX can check
if a vCPU is in kernel context if and only if the vCPU is loaded on the
current pCPU.
x86's kvm_arch_vcpu_in_kernel() works around the limitation by querying
kvm_get_running_vcpu() and redirecting to vcpu->arch.preempted_in_kernel
as needed. But that's unnecessary, confusing, and fragile, e.g. x86 has
had at least one bug where KVM incorrectly used a stale
preempted_in_kernel.
No functional change intended.
Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/20240110003938.490206-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 5 +++++
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 14 +++++++++++++-
3 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 019320580a848..94346490f4072 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -13054,6 +13054,11 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu)
return false;
}
+bool kvm_arch_vcpu_preempted_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return kvm_arch_vcpu_in_kernel(vcpu);
+}
+
bool kvm_arch_dy_runnable(struct kvm_vcpu *vcpu)
{
if (READ_ONCE(vcpu->arch.pv.pv_unhalted))
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 7e7fd25b09b3e..28b020404a41b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1505,6 +1505,7 @@ bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu);
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
bool kvm_arch_dy_runnable(struct kvm_vcpu *vcpu);
bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
+bool kvm_arch_vcpu_preempted_in_kernel(struct kvm_vcpu *vcpu);
int kvm_arch_post_init_vm(struct kvm *kvm);
void kvm_arch_pre_destroy_vm(struct kvm *kvm);
int kvm_arch_create_vm_debugfs(struct kvm *kvm);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 10bfc88a69f72..9b92858c8b72a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4042,6 +4042,18 @@ static bool vcpu_dy_runnable(struct kvm_vcpu *vcpu)
return false;
}
+/*
+ * By default, simply query the target vCPU's current mode when checking if a
+ * vCPU was preempted in kernel mode. All architectures except x86 (or more
+ * specifical, except VMX) allow querying whether or not a vCPU is in kernel
+ * mode even if the vCPU is NOT loaded, i.e. using kvm_arch_vcpu_in_kernel()
+ * directly for cross-vCPU checks is functionally correct and accurate.
+ */
+bool __weak kvm_arch_vcpu_preempted_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return kvm_arch_vcpu_in_kernel(vcpu);
+}
+
bool __weak kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu)
{
return false;
@@ -4080,7 +4092,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
continue;
if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
!kvm_arch_dy_has_pending_interrupt(vcpu) &&
- !kvm_arch_vcpu_in_kernel(vcpu))
+ !kvm_arch_vcpu_preempted_in_kernel(vcpu))
continue;
if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
continue;
--
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