On 15.08.2012, at 02:17, Scott Wood wrote: > On 08/14/2012 06:04 PM, Alexander Graf wrote: >> Generic KVM code might want to know whether we are inside guest context >> or outside. It also wants to be able to push us out of guest context. >> >> Add support to the BookE code for the generic vcpu->mode field that describes >> the above states. >> >> Signed-off-by: Alexander Graf <[email protected]> >> --- >> arch/powerpc/kvm/booke.c | 11 +++++++++++ >> 1 files changed, 11 insertions(+), 0 deletions(-) >> >> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c >> index bcf87fe..70a86c0 100644 >> --- a/arch/powerpc/kvm/booke.c >> +++ b/arch/powerpc/kvm/booke.c >> @@ -501,6 +501,15 @@ static int kvmppc_prepare_to_enter(struct kvm_vcpu >> *vcpu) >> continue; >> } >> >> + if (vcpu->mode == EXITING_GUEST_MODE) { >> + r = 1; >> + break; >> + } >> + >> + /* Going into guest context! Yay! */ >> + vcpu->mode = IN_GUEST_MODE; >> + smp_wmb(); >> + >> break; >> } > > Normally on entry to this function mode should be OUTSIDE_GUEST_MODE, > right? How could it possibly be EXITING_GUEST_MODE then, since that > only replaces IN_GUEST_MODE? > > This doesn't match what x86 does with mode on entry. Mode is supposed > to be set to IN_GUEST_MODE before requests are checked. > > I'm not sure what the point of EXITING_GUEST_MODE is at all, compared to > just waiting until after interrupts are disabled before setting > IN_GUEST_MODE (which we do on ppc, but not on x86 even though it seems > like a trivial change), plus the existing ordering between mode and > requests.
Well, the only real use case I could find for the mode was the remote vcpu kick. If we're not outside of guest mode, we get an IPI to notify us that requests are outstanding. So I only get us into OUTSIDE_GUEST_MODE when we really exit __vcpu_run, thus are in user space. That doesn't reflect what x86 does, right, but so doesn't our whole loop concept. However, since we might do the vcpu_block in this loop, we will never really get into OUTSIDE_GUEST_MODE, right? Hrm. So what would you suggest? Do all the handle_exit in OUTSIDE_GUEST_MODE scope and then reenter IN_GUEST_MODE in prepare_to_enter? We still wouldn't need an EXITING_GUEST_MODE though. Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
