On 15.08.2012, at 03:17, Scott Wood wrote: > On 08/14/2012 07:26 PM, Alexander Graf wrote: >> >> 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. > > I'm curious why this is done so differently for broadcast requests than > for single-cpu requests. > >> 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. > > OK. We still need to do ordering like x86 does, because otherwise > there's a race where we could check requests before the request bit is > set, and still have make_all_cpus_request see OUTSIDE_GUEST_MODE and not > send an IPI.
Could you please send a patch showing what workflow you envision? The code as is should work, just be inefficient at times, right? 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
