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@xxxxxxxxxx> 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
