[PATCH] KVM: arm64: vgic-v4: Make the doorbell request robust w.r.t preemption

[Zenghui Yu]

On 2023/7/13 15:06, Marc Zyngier 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. This occurs because when the vcpu thread is
> resumed on its way to block, vcpu_load() will make the vPE resident
> again. Once the vcpu actually blocks, we don't request a doorbell
> anymore, and the vcpu won't be woken up on interrupt delivery.
> 
> Fix it by tracking that we're entering WFI, and key the doorbell
> request on that flag. This allows us not to make the vPE resident
> when going through a preempt/schedule cycle, meaning we don't lose
> any state.
> 
> Cc: stable at 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 at hisilicon.com>
> Suggested-by: Zenghui Yu <yuzenghui at huawei.com>
> Tested-by: Xiang Chen <chenxiang66 at hisilicon.com>
> Co-developed-by: Oliver Upton <oliver.upton at linux.dev>
> Signed-off-by: Oliver Upton <oliver.upton at linux.dev>
> Signed-off-by: Marc Zyngier <maz at kernel.org>

Acked-by: Zenghui Yu <yuzenghui at huawei.com>