Re: [PATCH 2/3] Improve DEC handling
On Mon, Dec 21, 2009 at 6:22 AM, Alexander Graf ag...@suse.de wrote:
We treated the DEC interrupt like an edge based one. This is not true for
Book3s. The DEC keeps firing until mtdec is issued again and thus clears
the interrupt line.
That's not quite right. The decrementer keeps firing until the top bit
is cleared, i.e. with mtdec. However, not *every* mtdec clears it.
(Also, I'm pretty sure this varies between Book 3S implementations,
e.g. 970 behaves differently than POWERn. I don't remember specific
values of n though, and I could be misremembering...)
So is this the failure mode?
- a decrementer interrupt is delivered
- guest does *not* issue mtdec to clear it (ppc64's lazy interrupt disabling?)
- guest expects a second decrementer interrupt, but KVM doesn't deliver one
In that case, it seems like the real fix would be something like this:
void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
{
unsigned long dec_nsec;
pr_debug(mtDEC: %x\n, vcpu-arch.dec);
#ifdef CONFIG_PPC64
/* POWER4+ triggers a dec interrupt if the value is 0 */
if (vcpu-arch.dec 0x8000) {
hrtimer_try_to_cancel(vcpu-arch.dec_timer);
kvmppc_core_queue_dec(vcpu);
+ /* keep queuing interrupts until guest clears high MSR bit */
+ hrtimer_start(vcpu-arch.dec_timer, ktime_set(0, 100),
+ HRTIMER_MODE_REL);
return;
}
#endif
-Hollis
--
To unsubscribe from this list: send the line unsubscribe kvm-ppc in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 2/3] Improve DEC handling
On Mon, Dec 21, 2009 at 10:13 AM, Hollis Blanchard
hol...@penguinppc.org wrote:
void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
{
unsigned long dec_nsec;
pr_debug(mtDEC: %x\n, vcpu-arch.dec);
#ifdef CONFIG_PPC64
/* POWER4+ triggers a dec interrupt if the value is 0 */
if (vcpu-arch.dec 0x8000) {
hrtimer_try_to_cancel(vcpu-arch.dec_timer);
kvmppc_core_queue_dec(vcpu);
+ /* keep queuing interrupts until guest clears high MSR bit */
+ hrtimer_start(vcpu-arch.dec_timer, ktime_set(0, 100),
+ HRTIMER_MODE_REL);
return;
}
#endif
Of course, removing the hardcoded 100-ns timer would be better, and
indeed we can do that. What we *really* want is to key off of MSR[EE]
changes (there's no point in queuing anything until then). So why not
move your AGGRESSIVE_DEC check into Book 3S's kvmppc_set_msr()?
-Hollis
--
To unsubscribe from this list: send the line unsubscribe kvm-ppc in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 2/3] Improve DEC handling
Hollis Blanchard wrote:
On Mon, Dec 21, 2009 at 10:13 AM, Hollis Blanchard
hol...@penguinppc.org wrote:
void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
{
unsigned long dec_nsec;
pr_debug(mtDEC: %x\n, vcpu-arch.dec);
#ifdef CONFIG_PPC64
/* POWER4+ triggers a dec interrupt if the value is 0 */
if (vcpu-arch.dec 0x8000) {
hrtimer_try_to_cancel(vcpu-arch.dec_timer);
kvmppc_core_queue_dec(vcpu);
+ /* keep queuing interrupts until guest clears high MSR bit */
+ hrtimer_start(vcpu-arch.dec_timer, ktime_set(0, 100),
+ HRTIMER_MODE_REL);
return;
}
#endif
Of course, removing the hardcoded 100-ns timer would be better, and
indeed we can do that. What we *really* want is to key off of MSR[EE]
changes (there's no point in queuing anything until then).
Yes. mtmsr with EE=1 triggers a #VMEXIT which then goes off into a VM
entry which on entering checks that the DEC interrupt is still active
and fires it.
So why not
move your AGGRESSIVE_DEC check into Book 3S's kvmppc_set_msr()?
The idea was to get rid of AGGRESSIVE_DEC :-).
Alex
--
To unsubscribe from this list: send the line unsubscribe kvm-ppc in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
