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Re: [Qemu-block] [PULL 11/61] virtio-pci: use ioeventfd even when KVM is

From: QingFeng Hao
Subject: Re: [Qemu-block] [PULL 11/61] virtio-pci: use ioeventfd even when KVM is disabled
Date: Mon, 3 Jul 2017 14:01:45 +0800
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

在 2017/6/28 18:22, Kevin Wolf 写道:
Am 28.06.2017 um 12:11 hat QingFeng Hao geschrieben:
在 2017/6/24 0:21, Kevin Wolf 写道:
From: Stefan Hajnoczi <address@hidden>

Old kvm.ko versions only supported a tiny number of ioeventfds so
virtio-pci avoids ioeventfds when kvm_has_many_ioeventfds() returns 0.

Do not check kvm_has_many_ioeventfds() 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-blk-pci,iothread=iothread0 work even
when KVM is disabled.

I have tested that virtio-blk-pci works under TCG both with and without

Cc: Michael S. Tsirkin <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
Reviewed-by: Michael S. Tsirkin <address@hidden>
Signed-off-by: Kevin Wolf <address@hidden>
  hw/virtio/virtio-pci.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 20d6a08..301920e 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1740,7 +1740,7 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error 
      bool pcie_port = pci_bus_is_express(pci_dev->bus) &&

-    if (!kvm_has_many_ioeventfds()) {
+    if (kvm_enabled() && !kvm_has_many_ioeventfds()) {
          proxy->flags &= ~VIRTIO_PCI_FLAG_USE_IOEVENTFD;
This response is actually for mail thread "Re: [Qemu-devel] [PATCH
1/5] virtio-pci: use ioeventfd even when KVM is disabled"
which I didn't receive, sorry.
I also saw the failed case of 068 as Fam due to the same cause on
s390x and x86.
With this patch applied, no failure found. Further investigation
shows that the error is in
  if (!virtio_device_ioeventfd_enabled(vdev)) {
             error_setg(errp, "ioeventfd is required for iothread");
call flow is:
virtio_pci_ioeventfd_enabled checks flag
cleared in virtio_pci_realize if this patch isn't applied.
Yes, we know all of this. However, this patch is not correct and causes
'make check' failures on some platforms. The open question is where that
failure comes from. Before this is solved, the patch can't be applied.
Sorry that I found case 068 of the latest master still fails on s390x (but passed on x86) and the cause is that s390x uses "-device virtio-scsi-ccw" instead of "-device virtio-scsi-pci", so the change in virtio_ccw_device_realize is also needed:
diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index 90d37cb..35896eb 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
         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;

I'll send out a patch for that. Thanks!

QingFeng Hao

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