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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 019320580a848ed1c10e027c4239256f576a4cb0..94346490f407265d86dc902007e585d6910d4713 100644 (file)
--- 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 7e7fd25b09b3ebe3d81e30fb23f506a9ee5a6519..28b020404a41b8532453ed397bfb4a00c9bebff2 100644 (file)
--- 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 10bfc88a69f72b6a0e310cca043fb04882e24eb1..9b92858c8b72acfac046b4fe86193042be32c971 100644 (file)
--- 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;