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KVM: Add dedicated arch hook for querying if vCPU was preempted in-kernel

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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>
This commit is contained in:
Sean Christopherson 2024-01-09 16:39:35 -08:00
parent fc3c94142b
commit 77bcd9e623
3 changed files with 19 additions and 1 deletions
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5
arch/x86/kvm/x86.c
View file

@ -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))

1
include/linux/kvm_host.h
View file

@ -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);

14
virt/kvm/kvm_main.c
View file

@ -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;