On Mon, 10 Jul 2023 18:55:53 +0100, Oliver Upton oliver.upton@linux.dev wrote:
Xiang reports that VMs occasionally fail to boot on GICv4.1 systems when running a preemptible kernel, as it is possible that a vCPU is blocked without requesting a doorbell interrupt.
The issue is that any preemption that occurs between vgic_v4_put() and schedule() on the block path will mark the vPE as nonresident and *not* request a doorbell irq.
It'd be worth spelling out. You need to go via *three* schedule() calls: one to be preempted (with DB set), one to be made resident again, and then the final one in kvm_vcpu_halt(), clearing the DB on vcpu_put() due to the bug.
Fix it by consistently requesting a doorbell irq in the vcpu put path if the vCPU is blocking. While this technically means we could drop the early doorbell irq request in kvm_vcpu_wfi(), deliberately leave it intact such that vCPU halt polling can properly detect the wakeup condition before actually scheduling out a vCPU.
Cc: stable@vger.kernel.org Fixes: 8e01d9a396e6 ("KVM: arm64: vgic-v4: Move the GICv4 residency flow to be driven by vcpu_load/put") Reported-by: Xiang Chen chenxiang66@hisilicon.com Tested-by: Xiang Chen chenxiang66@hisilicon.com Signed-off-by: Oliver Upton oliver.upton@linux.dev
arch/arm64/kvm/vgic/vgic-v3.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c index c3b8e132d599..8c467e9f4f11 100644 --- a/arch/arm64/kvm/vgic/vgic-v3.c +++ b/arch/arm64/kvm/vgic/vgic-v3.c @@ -749,7 +749,7 @@ void vgic_v3_put(struct kvm_vcpu *vcpu) { struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
- WARN_ON(vgic_v4_put(vcpu, false));
- WARN_ON(vgic_v4_put(vcpu, kvm_vcpu_is_blocking(vcpu)));
vgic_v3_vmcr_sync(vcpu);
Other than the above nitpicking, this looks good. Thanks both for the very detailed report and the fix.
Reviewed-by: Marc Zyngier maz@kernel.org
M.