On Wed, Nov 07, 2018 at 06:01:20PM +0000, Mark Rutland wrote: > On Wed, Nov 07, 2018 at 05:10:31PM +0000, Alex Bennée wrote: > > Not all faults handled by handle_exit are instruction emulations. For > > example a ESR_ELx_EC_IABT will result in the page tables being updated > > but the instruction that triggered the fault hasn't actually executed > > yet. We use the simple heuristic of checking for a changed PC before > > seeing if kvm_arm_handle_step_debug wants to claim we stepped an > > instruction. > > > > Signed-off-by: Alex Bennée <[email protected]> > > --- > > arch/arm64/kvm/handle_exit.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > > index e5e741bfffe1..b8252e72f882 100644 > > --- a/arch/arm64/kvm/handle_exit.c > > +++ b/arch/arm64/kvm/handle_exit.c > > @@ -214,6 +214,7 @@ static exit_handle_fn kvm_get_exit_handler(struct > > kvm_vcpu *vcpu) > > static int handle_trap_exceptions(struct kvm_vcpu *vcpu, struct kvm_run > > *run) > > { > > int handled; > > + unsigned long old_pc = *vcpu_pc(vcpu); > > > > /* > > * See ARM ARM B1.14.1: "Hyp traps on instructions > > @@ -233,7 +234,8 @@ static int handle_trap_exceptions(struct kvm_vcpu > > *vcpu, struct kvm_run *run) > > * kvm_arm_handle_step_debug() sets the exit_reason on the kvm_run > > * structure if we need to return to userspace. > > */ > > - if (handled > 0 && kvm_arm_handle_step_debug(vcpu, run)) > > + if (handled > 0 && *vcpu_pc(vcpu) != old_pc && > > This doesn't work if the emulation is equivalent to a branch-to-self, so > I don't think that we want to do this. > > When are we failing to advance the single-step state machine correctly?
I don't understand how this is intended to work currently. Surely kvm_skip_instr() should advance the state machine as necessary, so that we can rely on the HW to generate any necessary single-step exception when we next return to the guest? ... and if userspace decides to emulate something, it's up to it to advance the state machine consistently. Thanks, Mark. _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
