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 5.10-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-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4868bd1fc77a5d2b5b59ff42b15dda0bcfce6256
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/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 5e5dd99e8cee..5bc978be8043 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1143,6 +1143,14 @@ 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
