Hi Marc,
KVM: arm64: Commit pending PC adjustemnts before returning to userspace
s/adjustments/adjustments
On Mon, May 10, 2021 at 10:49 AM Marc Zyngier maz@kernel.org wrote:
KVM currently updates PC (and the corresponding exception state) using a two phase approach: first by setting a set of flags, then by converting these flags into a state update when the vcpu is about to enter the guest.
However, this creates a disconnect with userspace if the vcpu thread returns there with any exception/PC flag set. In this case, the exposed context is wrong, as userpsace doesn't have access to these flags (they aren't architectural). It also means that these flags are preserved across a reset, which isn't expected.
To solve this problem, force an explicit synchronisation of the exception state on vcpu exit to userspace. As an optimisation for nVHE systems, only perform this when there is something pending.
I've tested this with a few nvhe and vhe tests that exercise both __kvm_adjust_pc call paths (__kvm_vcpu_run and kvm_arch_vcpu_ioctl_run), and the tests ran as expected. I'll do the same for v2 when you send it out.
Cheers, /fuad