On 19/11/2019 01:47, David Gibson wrote:
> On Mon, Nov 18, 2019 at 04:37:16PM +0100, Cédric Le Goater wrote:
>> On 18/11/2019 16:12, Greg Kurz wrote:
>>> When using the XIVE KVM device, the trigger page is directly accessible
>>> in QEMU. Unlike with XICS, no need to ask KVM to fire the interrupt. A
>>> simple store on the trigger page does the job.
>>>
>>> Just call xive_esb_trigger().
>>
>> Yes but the KVM XIVE device does a few other checks.
>>
>> It checks that the interrupt was correctly initialized at the KVM device
>> level. We should be fine in QEMU which has similar checks.
>>
>> It caches the LSI assertion level. We should be fine also because it is
>> useless in KVM when using the XIVE native exploitation mode.
>>
>> It checks it is not a passthru interrupt. Any idea on how to check this
>> condition under QEMU ?
>>
>>> This may improve performance of emulated devices that go through
>>> qemu_set_irq(), eg. virtio devices created with ioeventfd=off or
>>> configured by the guest to use LSI interrupts, which aren't really
>>> recommended setups.
>>
>> LGTM.
>
> Ok, between the comments above and this, I'm not sure if this is ready
> to merge or not.
I think it is.
With this change, we are loosing a check on passthrough interrupts but
I am not sure how critical this is given that QEMU can anyhow bypass
KVM and trigger the interrupt using a store on the ESB page.
>> Any figures to share ?
I am torturing Greg to have numbers :) but he resisted well.
>> C.
>>
>>> Signed-off-by: Greg Kurz <gr...@kaod.org>
Let's move on.
Reviewed-by: Cédric Le Goater <c...@kaod.org>
C.
>>> ---
>>> hw/intc/spapr_xive_kvm.c | 16 ++--------------
>>> 1 file changed, 2 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/hw/intc/spapr_xive_kvm.c b/hw/intc/spapr_xive_kvm.c
>>> index 08012ac7cd76..69e73552f1ef 100644
>>> --- a/hw/intc/spapr_xive_kvm.c
>>> +++ b/hw/intc/spapr_xive_kvm.c
>>> @@ -354,32 +354,20 @@ static void kvmppc_xive_source_get_state(XiveSource
>>> *xsrc)
>>> void kvmppc_xive_source_set_irq(void *opaque, int srcno, int val)
>>> {
>>> XiveSource *xsrc = opaque;
>>> - SpaprXive *xive = SPAPR_XIVE(xsrc->xive);
>>> - struct kvm_irq_level args;
>>> - int rc;
>>> -
>>> - /* The KVM XIVE device should be in use */
>>> - assert(xive->fd != -1);
>>>
>>> - args.irq = srcno;
>>> if (!xive_source_irq_is_lsi(xsrc, srcno)) {
>>> if (!val) {
>>> return;
>>> }
>>> - args.level = KVM_INTERRUPT_SET;
>>> } else {
>>> if (val) {
>>> xsrc->status[srcno] |= XIVE_STATUS_ASSERTED;
>>> - args.level = KVM_INTERRUPT_SET_LEVEL;
>>> } else {
>>> xsrc->status[srcno] &= ~XIVE_STATUS_ASSERTED;
>>> - args.level = KVM_INTERRUPT_UNSET;
>>> }
>>> }
>>> - rc = kvm_vm_ioctl(kvm_state, KVM_IRQ_LINE, &args);
>>> - if (rc < 0) {
>>> - error_report("XIVE: kvm_irq_line() failed : %s", strerror(errno));
>>> - }
>>> +
>>> + xive_esb_trigger(xsrc, srcno);
>>> }
>>
>>
>
