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Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/1] virtio-scsi-ccw: use ioeven


From: Christian Borntraeger
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/1] virtio-scsi-ccw: use ioeventfd even when KVM is disabled
Date: Mon, 3 Jul 2017 12:20:03 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0

On 07/03/2017 10:51 AM, QingFeng Hao wrote:
> This patch is based on a similar patch from Stefan Hajnoczi -
> commit c324fd0a39c (" virtio-pci: use ioeventfd even when KVM is disabled)
> 
> Do not check kvm_eventfds_enabled() when KVM is disabled since it
> always returns 0.  Since commit 8c56c1a592b5092d91da8d8943c17777d6462a6f
> ("memory: emulate ioeventfd") it has been possible to use ioeventfds in
> qtest or TCG mode.
> 
> This patch makes -device virtio-scsi-ccw,iothread=iothread0 work even
> when KVM is disabled.
> 
> I have tested that virtio-scsi-ccw works under tcg both with and without
> iothread.
> 
> This patch fixes qemu-iotests 068, which was accidentally merged early
> despite the dependency on ioeventfd.
> 
> Signed-off-by: QingFeng Hao <address@hidden>
> ---
>  hw/s390x/virtio-ccw.c | 2 +-
>  target/s390x/kvm.c    | 3 +++
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
> index 90d37cb9ff..35896eb007 100644
> --- a/hw/s390x/virtio-ccw.c
> +++ b/hw/s390x/virtio-ccw.c
> @@ -711,7 +711,7 @@ static void virtio_ccw_device_realize(VirtioCcwDevice 
> *dev, Error **errp)
>          sch->cssid, sch->ssid, sch->schid, sch->devno,
>          ccw_dev->devno.valid ? "user-configured" : "auto-configured");
> 
> -    if (!kvm_eventfds_enabled()) {
> +    if (kvm_enabled() && !kvm_eventfds_enabled()) {
>          dev->flags &= ~VIRTIO_CCW_FLAG_USE_IOEVENTFD;
>      }
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index a3d00196f4..c37f9c3b9e 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -2220,6 +2220,9 @@ int kvm_s390_assign_subch_ioeventfd(EventNotifier 
> *notifier, uint32_t sch,
>          .addr = sch,
>          .len = 8,
>      };
> +    if (!kvm_enabled()) {
> +        return 0;
> +    }

thinking more about it. wouldnt it be better to do something like this instead

diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
index 058ddad..cc47831 100644
--- a/target/s390x/cpu.h
+++ b/target/s390x/cpu.h
@@ -1240,7 +1240,11 @@ static inline int 
s390_assign_subch_ioeventfd(EventNotifier *notifier,
                                               uint32_t sch_id, int vq,
                                               bool assign)
 {
-    return kvm_s390_assign_subch_ioeventfd(notifier, sch_id, vq, assign);
+    if (kvm_enabled()) {
+        return kvm_s390_assign_subch_ioeventfd(notifier, sch_id, vq, assign);
+    } else {
+        return 0;
+    }
 }
 
 static inline void s390_crypto_reset(void)


FWIW, it seems that we (s390) do not have a functional equivalent function as 
commit
8c56c1a592b5092d91da8d8943c17777d6462a6f ("memory: emulate ioeventfd") , so we 
will
not use the iothreads. 


>      if (!kvm_check_extension(kvm_state, KVM_CAP_IOEVENTFD)) {
>          return -ENOSYS;
>      }
> 




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