Re: [RFC 12/37] KVM: s390: protvirt: Handle SE notification interceptions

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On Tue, 5 Nov 2019 19:15:19 +0100
Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote:

> On 05.11.19 19:04, Cornelia Huck wrote:
> > On Thu, 24 Oct 2019 07:40:34 -0400
> > Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:
> >   
> >> Since KVM doesn't emulate any form of load control and load psw
> >> instructions anymore, we wouldn't get an interception if PSWs or CRs
> >> are changed in the guest. That means we can't inject IRQs right after
> >> the guest is enabled for them.
> >>
> >> The new interception codes solve that problem by being a notification
> >> for changes to IRQ enablement relevant bits in CRs 0, 6 and 14, as
> >> well a the machine check mask bit in the PSW.
> >>
> >> No special handling is needed for these interception codes, the KVM
> >> pre-run code will consult all necessary CRs and PSW bits and inject
> >> IRQs the guest is enabled for.  
> > 
> > Just to clarify: The hypervisor can still access the relevant bits for
> > pv guests, this is only about the notification, right?
> >   
> 
> Yes, the hypervisor (KVM) can always read the relevant PSW bits (I,E,M) and
> CR bits to decide if an interrupt can be delivered. All other bits of PSW
> and CRx are masked though.
> This is a new intercept for notification as we do no longer get an IC4 (instruction
> to handle) for load control and friends so that we can re-check the bits. 

Ok, thanks!

> >>
> >> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
> >> ---
> >>  arch/s390/include/asm/kvm_host.h |  2 ++
> >>  arch/s390/kvm/intercept.c        | 18 ++++++++++++++++++
> >>  2 files changed, 20 insertions(+)  
> >   
> 





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