This is a note to let you know that I've just added the patch titled KVM: arm64: Handle PSCI resets before userspace touches vCPU state to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-arm64-handle-psci-resets-before-userspace-touche.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit c9757243add646f6fdfa6e458648280ebd8f08c8 Author: Oliver Upton <oupton@xxxxxxxxxx> Date: Wed Aug 18 20:21:31 2021 +0000 KVM: arm64: Handle PSCI resets before userspace touches vCPU state [ Upstream commit 6826c6849b46aaa91300201213701eb861af4ba0 ] The CPU_ON PSCI call takes a payload that KVM uses to configure a destination vCPU to run. This payload is non-architectural state and not exposed through any existing UAPI. Effectively, we have a race between CPU_ON and userspace saving/restoring a guest: if the target vCPU isn't ran again before the VMM saves its state, the requested PC and context ID are lost. When restored, the target vCPU will be runnable and start executing at its old PC. We can avoid this race by making sure the reset payload is serviced before userspace can access a vCPU's state. Fixes: 358b28f09f0a ("arm/arm64: KVM: Allow a VCPU to fully reset itself") Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> Link: https://lore.kernel.org/r/20210818202133.1106786-3-oupton@xxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index 4af85605730e..f7150fbeeb55 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -1141,6 +1141,14 @@ long kvm_arch_vcpu_ioctl(struct file *filp, if (copy_from_user(®, argp, sizeof(reg))) break; + /* + * We could owe a reset due to PSCI. Handle the pending reset + * here to ensure userspace register accesses are ordered after + * the reset. + */ + if (kvm_check_request(KVM_REQ_VCPU_RESET, vcpu)) + kvm_reset_vcpu(vcpu); + if (ioctl == KVM_SET_ONE_REG) r = kvm_arm_set_reg(vcpu, ®); else