QEMU-4.1 supports 'Direct Mode' for Hyper-V synthetic timers
(hv-stimer-direct CPU flag): Windows guests can request that timer
expiration notifications are delivered as normal interrupts (and not
VMBus messages). This is used by Hyper-V on KVM.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 src/qemu/qemu_command.c             | 12 ++++++++----
 src/qemu/qemu_process.c             | 20 ++++++++++++++++++--
 tests/qemuxml2argvdata/hyperv.args  |  4 ++--
 tests/qemuxml2argvdata/hyperv.xml   |  4 +++-
 tests/qemuxml2xmloutdata/hyperv.xml |  4 +++-
 5 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index c8494de785..af913dba34 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -7152,10 +7152,10 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
     }
 
     if (def->features[VIR_DOMAIN_FEATURE_HYPERV] == VIR_TRISTATE_SWITCH_ON) {
-        const char *hvPrefix = "hv-";
+        const char *hvDelimiter = "-";
 
         if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_CANONICAL_CPU_FEATURES))
-            hvPrefix = "hv_";
+            hvDelimiter = "_";
 
         for (i = 0; i < VIR_DOMAIN_HYPERV_LAST; i++) {
             switch ((virDomainHyperv) i) {
@@ -7172,9 +7172,13 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
             case VIR_DOMAIN_HYPERV_IPI:
             case VIR_DOMAIN_HYPERV_EVMCS:
                 if (def->hyperv_features[i] == VIR_TRISTATE_SWITCH_ON)
-                    virBufferAsprintf(&buf, ",%s%s",
-                                      hvPrefix,
+                    virBufferAsprintf(&buf, ",hv%s%s",
+                                      hvDelimiter,
                                       virDomainHypervTypeToString(i));
+                if ((i == VIR_DOMAIN_HYPERV_STIMER) &&
+                    (def->hyperv_stimer_direct == VIR_TRISTATE_SWITCH_ON))
+                    virBufferAsprintf(&buf, ",hv%sstimer%sdirect", hvDelimiter,
+                                      hvDelimiter);
                 break;
 
             case VIR_DOMAIN_HYPERV_SPINLOCKS:
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 1ed56457b1..792fa33327 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -4112,10 +4112,26 @@ qemuProcessVerifyHypervFeatures(virDomainDefPtr def,
         rc = virCPUDataCheckFeature(cpu, cpuFeature);
         VIR_FREE(cpuFeature);
 
-        if (rc < 0)
+        if (rc < 0) {
             return -1;
-        else if (rc == 1)
+        } else if (rc == 1) {
+            if (i == VIR_DOMAIN_HYPERV_STIMER) {
+                if (def->hyperv_stimer_direct != VIR_TRISTATE_SWITCH_ON)
+                    continue;
+
+                rc = virCPUDataCheckFeature(cpu, "hv-stimer-direct");
+                if (rc < 0)
+                    return -1;
+                else if (rc == 1)
+                    continue;
+
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                               _("host doesn't support hyperv stimer '%s' feature"),
+                               "direct");
+                return -1;
+            }
             continue;
+        }
 
         switch ((virDomainHyperv) i) {
         case VIR_DOMAIN_HYPERV_RELAXED:
diff --git a/tests/qemuxml2argvdata/hyperv.args b/tests/qemuxml2argvdata/hyperv.args
index 086adaa349..8040da9caa 100644
--- a/tests/qemuxml2argvdata/hyperv.args
+++ b/tests/qemuxml2argvdata/hyperv.args
@@ -12,8 +12,8 @@ QEMU_AUDIO_DRV=none \
 -S \
 -machine pc,accel=tcg,usb=off,dump-guest-core=off \
 -cpu 'qemu32,hv_relaxed,hv_vapic,hv-spinlocks=0x2fff,hv_vpindex,hv_runtime,\
-hv_synic,hv_stimer,hv_reset,hv-vendor-id=KVM Hv,hv_frequencies,\
-hv_reenlightenment,hv_tlbflush,hv_ipi,hv_evmcs' \
+hv_synic,hv_stimer,hv_stimer_direct,hv_reset,hv-vendor-id=KVM Hv,\
+hv_frequencies,hv_reenlightenment,hv_tlbflush,hv_ipi,hv_evmcs' \
 -m 214 \
 -realtime mlock=off \
 -smp 6,sockets=6,cores=1,threads=1 \
diff --git a/tests/qemuxml2argvdata/hyperv.xml b/tests/qemuxml2argvdata/hyperv.xml
index c6feaed528..ae0f934f76 100644
--- a/tests/qemuxml2argvdata/hyperv.xml
+++ b/tests/qemuxml2argvdata/hyperv.xml
@@ -17,7 +17,9 @@
       <vpindex state='on'/>
       <runtime state='on'/>
       <synic state='on'/>
-      <stimer state='on'/>
+      <stimer state='on'>
+        <direct state='on'/>
+      </stimer>
       <reset state='on'/>
       <vendor_id state='on' value='KVM Hv'/>
       <frequencies state='on'/>
diff --git a/tests/qemuxml2xmloutdata/hyperv.xml b/tests/qemuxml2xmloutdata/hyperv.xml
index 5510d3dfad..2e4b43d4c6 100644
--- a/tests/qemuxml2xmloutdata/hyperv.xml
+++ b/tests/qemuxml2xmloutdata/hyperv.xml
@@ -17,7 +17,9 @@
       <vpindex state='on'/>
       <runtime state='on'/>
       <synic state='on'/>
-      <stimer state='on'/>
+      <stimer state='on'>
+        <direct state='on'/>
+      </stimer>
       <reset state='on'/>
       <vendor_id state='on' value='KVM Hv'/>
       <frequencies state='on'/>
-- 
2.20.1

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On Tue, Aug 06, 2019 at 07:52:35AM +0200, Vitaly Kuznetsov wrote:
>QEMU-4.1 supports 'Direct Mode' for Hyper-V synthetic timers
>(hv-stimer-direct CPU flag): Windows guests can request that timer
>expiration notifications are delivered as normal interrupts (and not
>VMBus messages). This is used by Hyper-V on KVM.
>
>Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>---
> src/qemu/qemu_command.c             | 12 ++++++++----
> src/qemu/qemu_process.c             | 20 ++++++++++++++++++--
> tests/qemuxml2argvdata/hyperv.args  |  4 ++--
> tests/qemuxml2argvdata/hyperv.xml   |  4 +++-
> tests/qemuxml2xmloutdata/hyperv.xml |  4 +++-
> 5 files changed, 34 insertions(+), 10 deletions(-)
>
>diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
>index c8494de785..af913dba34 100644
>--- a/src/qemu/qemu_command.c
>+++ b/src/qemu/qemu_command.c
>@@ -7152,10 +7152,10 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
>     }
>
>     if (def->features[VIR_DOMAIN_FEATURE_HYPERV] == VIR_TRISTATE_SWITCH_ON) {
>-        const char *hvPrefix = "hv-";
>+        const char *hvDelimiter = "-";
>
>         if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_CANONICAL_CPU_FEATURES))
>-            hvPrefix = "hv_";
>+            hvDelimiter = "_";
>
>         for (i = 0; i < VIR_DOMAIN_HYPERV_LAST; i++) {
>             switch ((virDomainHyperv) i) {
>@@ -7172,9 +7172,13 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
>             case VIR_DOMAIN_HYPERV_IPI:
>             case VIR_DOMAIN_HYPERV_EVMCS:
>                 if (def->hyperv_features[i] == VIR_TRISTATE_SWITCH_ON)
>-                    virBufferAsprintf(&buf, ",%s%s",
>-                                      hvPrefix,
>+                    virBufferAsprintf(&buf, ",hv%s%s",
>+                                      hvDelimiter,
>                                       virDomainHypervTypeToString(i));
>+                if ((i == VIR_DOMAIN_HYPERV_STIMER) &&
>+                    (def->hyperv_stimer_direct == VIR_TRISTATE_SWITCH_ON))
>+                    virBufferAsprintf(&buf, ",hv%sstimer%sdirect", hvDelimiter,
>+                                      hvDelimiter);

IIUC this feature will be introduced in QEMU 4.1.0 which is the one
where we stop using the aliases with underscores, so this can be
",hv-stimer-direct" and the hvDelimiter changes are not needed.

With that changed:

Reviewed-by: Ján Tomko <jtomko@redhat.com>

Jano
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On Tue, Aug 06, 2019 at 01:25:37PM +0200, Ján Tomko wrote:
>On Tue, Aug 06, 2019 at 07:52:35AM +0200, Vitaly Kuznetsov wrote:
>>QEMU-4.1 supports 'Direct Mode' for Hyper-V synthetic timers
>>(hv-stimer-direct CPU flag): Windows guests can request that timer
>>expiration notifications are delivered as normal interrupts (and not
>>VMBus messages). This is used by Hyper-V on KVM.
>>
>>Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>>---
>>src/qemu/qemu_command.c             | 12 ++++++++----
>>src/qemu/qemu_process.c             | 20 ++++++++++++++++++--
>>tests/qemuxml2argvdata/hyperv.args  |  4 ++--
>>tests/qemuxml2argvdata/hyperv.xml   |  4 +++-
>>tests/qemuxml2xmloutdata/hyperv.xml |  4 +++-
>>5 files changed, 34 insertions(+), 10 deletions(-)
>>
>>diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
>>index c8494de785..af913dba34 100644
>>--- a/src/qemu/qemu_command.c
>>+++ b/src/qemu/qemu_command.c
>>@@ -7152,10 +7152,10 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
>>    }
>>
>>    if (def->features[VIR_DOMAIN_FEATURE_HYPERV] == VIR_TRISTATE_SWITCH_ON) {
>>-        const char *hvPrefix = "hv-";
>>+        const char *hvDelimiter = "-";
>>
>>        if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_CANONICAL_CPU_FEATURES))
>>-            hvPrefix = "hv_";
>>+            hvDelimiter = "_";
>>
>>        for (i = 0; i < VIR_DOMAIN_HYPERV_LAST; i++) {
>>            switch ((virDomainHyperv) i) {
>>@@ -7172,9 +7172,13 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
>>            case VIR_DOMAIN_HYPERV_IPI:
>>            case VIR_DOMAIN_HYPERV_EVMCS:
>>                if (def->hyperv_features[i] == VIR_TRISTATE_SWITCH_ON)
>>-                    virBufferAsprintf(&buf, ",%s%s",
>>-                                      hvPrefix,
>>+                    virBufferAsprintf(&buf, ",hv%s%s",
>>+                                      hvDelimiter,
>>                                      virDomainHypervTypeToString(i));
>>+                if ((i == VIR_DOMAIN_HYPERV_STIMER) &&
>>+                    (def->hyperv_stimer_direct == VIR_TRISTATE_SWITCH_ON))
>>+                    virBufferAsprintf(&buf, ",hv%sstimer%sdirect", hvDelimiter,
>>+                                      hvDelimiter);
>
>IIUC this feature will be introduced in QEMU 4.1.0 which is the one
>where we stop using the aliases with underscores, so this can be
>",hv-stimer-direct" and the hvDelimiter changes are not needed.
>

Or even the VIR_CPU_x86_HV_STIMER_DIRECT string instead.

One more thing, qemuxml2argvtest is using DO_TEST:
    DO_TEST("hyperv", NONE);
    DO_TEST("hyperv-off", NONE);
    DO_TEST("hyperv-panic", NONE);
which manually enumarate the used QEMU capabilities (although there are
none here)

DO_TEST_CAPS_LATEST is the way to test against QEMU capabilites
gathered from a real binary - if you use that macro for testing,
it will have the QEMU_CAPS_CANONICAL_CPU_FEATURES capability and all the
included features will use '-' instead of '_' as the separator.

Jano

>With that changed:
>
>Reviewed-by: Ján Tomko <jtomko@redhat.com>
>
>Jano



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Ján Tomko <jtomko@redhat.com> writes:

> One more thing, qemuxml2argvtest is using DO_TEST:
>     DO_TEST("hyperv", NONE);
>     DO_TEST("hyperv-off", NONE);
>     DO_TEST("hyperv-panic", NONE);
> which manually enumarate the used QEMU capabilities (although there are
> none here)
>
> DO_TEST_CAPS_LATEST is the way to test against QEMU capabilites
> gathered from a real binary - if you use that macro for testing,
> it will have the QEMU_CAPS_CANONICAL_CPU_FEATURES capability and all the
> included features will use '-' instead of '_' as the separator.
>

Forgive me my ignorance (and long reply times), is the idea aimed at
removing "hvPrefix" machinery from qemuBuildCpuCommandLine() completely
- probably in favor of hardcorded '-' delimiters?

I tried switching to DO_TEST_CAPS_LATEST in qemuxml2argvtest and after
renaming
tests/qemuxml2argvdata/hyperv{-off,-panic}.args to
tests/qemuxml2argvdata/hyperv{,-off,-panic}.x86_64-latest.args
to make the test run, I'm getting the following:

In '/home/vitty/workspace/Upstream/libvirt/tests/qemuxml2argvdata/hyperv.x86_64-latest.args':
Offset 292
Expect [QEMUGuest1 -S -machine pc,accel=tcg,usb=off,dump-guest-core=off -cpu 'qemu32,hv-relaxed,hv-vapic,hv-spinlocks=0x2fff,hv-vpindex,hv-runtime,hv-synic,hv-stimer,hv-reset,hv-vendor-id=KVM Hv,hv-frequencies,hv-reenlightenment,hv-tlbflush,hv-ipi,hv-evmcs' -m 214 -realtime mlock=off -smp 6,sockets=6,cores=1,threads=1 -uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 -display none -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/tmp/lib/domain--1-QEMUGuest1/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -usb]
Actual [guest=QEMUGuest1,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes -machine pc,accel=tcg,usb=off,dump-guest-core=off -cpu 'qemu32,hv-relaxed,hv-vapic,hv-spinlocks=0x2fff,hv-vpindex,hv-runtime,hv-synic,hv-stimer,hv-reset,hv-vendor-id=KVM Hv,hv-frequencies,hv-reenlightenment,hv-tlbflush,hv-ipi,hv-evmcs' -m 214 -overcommit mem-lock=off -smp 6,sockets=6,cores=1,threads=1 -uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 -display none -no-user-config -nodefaults -chardev socket,id=charmonitor,fd=1729,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -msg timestamp=on]
 
I can, probably, add all the missing stuff but I'm not sure it's the
right way to go in the first place :-)

What if we just add QEMU_CAPS_CANONICAL_CPU_FEATURES to DO_TEST:

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 71a36ff63a..f88d45f4e6 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -7152,11 +7152,6 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
     }
 
     if (def->features[VIR_DOMAIN_FEATURE_HYPERV] == VIR_TRISTATE_SWITCH_ON) {
-        const char *hvPrefix = "hv-";
-
-        if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_CANONICAL_CPU_FEATURES))
-            hvPrefix = "hv_";
-
         for (i = 0; i < VIR_DOMAIN_HYPERV_LAST; i++) {
             switch ((virDomainHyperv) i) {
             case VIR_DOMAIN_HYPERV_RELAXED:
@@ -7172,8 +7167,7 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
             case VIR_DOMAIN_HYPERV_IPI:
             case VIR_DOMAIN_HYPERV_EVMCS:
                 if (def->hyperv_features[i] == VIR_TRISTATE_SWITCH_ON)
-                    virBufferAsprintf(&buf, ",%s%s",
-                                      hvPrefix,
+                    virBufferAsprintf(&buf, ",hv-%s",
                                       virDomainHypervTypeToString(i));
                 break;
 
diff --git a/tests/qemuxml2argvdata/hyperv.args b/tests/qemuxml2argvdata/hyperv.args
index 086adaa349..d09d8acdff 100644
--- a/tests/qemuxml2argvdata/hyperv.args
+++ b/tests/qemuxml2argvdata/hyperv.args
@@ -11,9 +11,9 @@ QEMU_AUDIO_DRV=none \
 -name QEMUGuest1 \
 -S \
 -machine pc,accel=tcg,usb=off,dump-guest-core=off \
--cpu 'qemu32,hv_relaxed,hv_vapic,hv-spinlocks=0x2fff,hv_vpindex,hv_runtime,\
-hv_synic,hv_stimer,hv_reset,hv-vendor-id=KVM Hv,hv_frequencies,\
-hv_reenlightenment,hv_tlbflush,hv_ipi,hv_evmcs' \
+-cpu 'qemu32,hv-relaxed,hv-vapic,hv-spinlocks=0x2fff,hv-vpindex,hv-runtime,\
+hv-synic,hv-stimer,hv-reset,hv-vendor-id=KVM Hv,hv-frequencies,\
+hv-reenlightenment,hv-tlbflush,hv-ipi,hv-evmcs' \
 -m 214 \
 -realtime mlock=off \
 -smp 6,sockets=6,cores=1,threads=1 \
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index c166fd18d6..d13c7c8b56 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -911,9 +911,9 @@ mymain(void)
     DO_TEST_CAPS_VER("kvmclock+eoi-disabled", "4.0.0");
     DO_TEST_CAPS_LATEST("kvmclock+eoi-disabled");
 
-    DO_TEST("hyperv", NONE);
-    DO_TEST("hyperv-off", NONE);
-    DO_TEST("hyperv-panic", NONE);
+    DO_TEST("hyperv", QEMU_CAPS_CANONICAL_CPU_FEATURES);
+    DO_TEST("hyperv-off", QEMU_CAPS_CANONICAL_CPU_FEATURES);
+    DO_TEST("hyperv-panic", QEMU_CAPS_CANONICAL_CPU_FEATURES);
 
     DO_TEST("kvm-features", NONE);
     DO_TEST("kvm-features-off", NONE);

-- 
Vitaly

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On Fri, Aug 09, 2019 at 12:13:45PM +0200, Vitaly Kuznetsov wrote:
>Ján Tomko <jtomko@redhat.com> writes:
>
>> One more thing, qemuxml2argvtest is using DO_TEST:
>>     DO_TEST("hyperv", NONE);
>>     DO_TEST("hyperv-off", NONE);
>>     DO_TEST("hyperv-panic", NONE);
>> which manually enumarate the used QEMU capabilities (although there are
>> none here)
>>
>> DO_TEST_CAPS_LATEST is the way to test against QEMU capabilites
>> gathered from a real binary - if you use that macro for testing,
>> it will have the QEMU_CAPS_CANONICAL_CPU_FEATURES capability and all the
>> included features will use '-' instead of '_' as the separator.
>>
>
>Forgive me my ignorance (and long reply times), is the idea aimed at
>removing "hvPrefix" machinery from qemuBuildCpuCommandLine() completely
>- probably in favor of hardcorded '-' delimiters?
>

For new features that will not be used with QEMU <4.1, which does
not have QEMU_CAPS_CANONICAL_CPU_FEATURES we should hardcode the version
with the '-' delimiter.

>I tried switching to DO_TEST_CAPS_LATEST in qemuxml2argvtest and after
>renaming
>tests/qemuxml2argvdata/hyperv{-off,-panic}.args to
>tests/qemuxml2argvdata/hyperv{,-off,-panic}.x86_64-latest.args
>to make the test run, I'm getting the following:
>
>In '/home/vitty/workspace/Upstream/libvirt/tests/qemuxml2argvdata/hyperv.x86_64-latest.args':
>Offset 292
>Expect [QEMUGuest1 -S -machine pc,accel=tcg,usb=off,dump-guest-core=off -cpu 'qemu32,hv-relaxed,hv-vapic,hv-spinlocks=0x2fff,hv-vpindex,hv-runtime,hv-synic,hv-stimer,hv-reset,hv-vendor-id=KVM Hv,hv-frequencies,hv-reenlightenment,hv-tlbflush,hv-ipi,hv-evmcs' -m 214 -realtime mlock=off -smp 6,sockets=6,cores=1,threads=1 -uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 -display none -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/tmp/lib/domain--1-QEMUGuest1/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -usb]
>Actual [guest=QEMUGuest1,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes -machine pc,accel=tcg,usb=off,dump-guest-core=off -cpu 'qemu32,hv-relaxed,hv-vapic,hv-spinlocks=0x2fff,hv-vpindex,hv-runtime,hv-synic,hv-stimer,hv-reset,hv-vendor-id=KVM Hv,hv-frequencies,hv-reenlightenment,hv-tlbflush,hv-ipi,hv-evmcs' -m 214 -overcommit mem-lock=off -smp 6,sockets=6,cores=1,threads=1 -uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 -display none -no-user-config -nodefaults -chardev socket,id=charmonitor,fd=1729,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -msg timestamp=on]
>

From a glance all these changes look OK and are a result of using newer
syntax for the same options.

To easily regenerate the output, set the env variable VIR_TEST_REGENERATE_OUTPUT=1 before running
the test.

>I can, probably, add all the missing stuff but I'm not sure it's the
>right way to go in the first place :-)
>
>What if we just add QEMU_CAPS_CANONICAL_CPU_FEATURES to DO_TEST:
>

We try to steer away from enumerating capabilites in the tests.

>diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
>index 71a36ff63a..f88d45f4e6 100644
>--- a/src/qemu/qemu_command.c
>+++ b/src/qemu/qemu_command.c
>@@ -7152,11 +7152,6 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
>     }
>
>     if (def->features[VIR_DOMAIN_FEATURE_HYPERV] == VIR_TRISTATE_SWITCH_ON) {
>-        const char *hvPrefix = "hv-";
>-
>-        if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_CANONICAL_CPU_FEATURES))
>-            hvPrefix = "hv_";
>-

IIUC we still need this code to deal with older QEMU. It's just new
QEMUs where we can use the unified '-' delimiter.

>         for (i = 0; i < VIR_DOMAIN_HYPERV_LAST; i++) {
>             switch ((virDomainHyperv) i) {
>             case VIR_DOMAIN_HYPERV_RELAXED:
>@@ -7172,8 +7167,7 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
>             case VIR_DOMAIN_HYPERV_IPI:
>             case VIR_DOMAIN_HYPERV_EVMCS:
>                 if (def->hyperv_features[i] == VIR_TRISTATE_SWITCH_ON)
>-                    virBufferAsprintf(&buf, ",%s%s",
>-                                      hvPrefix,
>+                    virBufferAsprintf(&buf, ",hv-%s",
>                                       virDomainHypervTypeToString(i));
>                 break;
>
>diff --git a/tests/qemuxml2argvdata/hyperv.args b/tests/qemuxml2argvdata/hyperv.args
>index 086adaa349..d09d8acdff 100644
>--- a/tests/qemuxml2argvdata/hyperv.args
>+++ b/tests/qemuxml2argvdata/hyperv.args
>@@ -11,9 +11,9 @@ QEMU_AUDIO_DRV=none \
> -name QEMUGuest1 \
> -S \
> -machine pc,accel=tcg,usb=off,dump-guest-core=off \
>--cpu 'qemu32,hv_relaxed,hv_vapic,hv-spinlocks=0x2fff,hv_vpindex,hv_runtime,\
>-hv_synic,hv_stimer,hv_reset,hv-vendor-id=KVM Hv,hv_frequencies,\
>-hv_reenlightenment,hv_tlbflush,hv_ipi,hv_evmcs' \
>+-cpu 'qemu32,hv-relaxed,hv-vapic,hv-spinlocks=0x2fff,hv-vpindex,hv-runtime,\
>+hv-synic,hv-stimer,hv-reset,hv-vendor-id=KVM Hv,hv-frequencies,\
>+hv-reenlightenment,hv-tlbflush,hv-ipi,hv-evmcs' \
> -m 214 \
> -realtime mlock=off \
> -smp 6,sockets=6,cores=1,threads=1 \
>diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
>index c166fd18d6..d13c7c8b56 100644
>--- a/tests/qemuxml2argvtest.c
>+++ b/tests/qemuxml2argvtest.c
>@@ -911,9 +911,9 @@ mymain(void)
>     DO_TEST_CAPS_VER("kvmclock+eoi-disabled", "4.0.0");
>     DO_TEST_CAPS_LATEST("kvmclock+eoi-disabled");
>
>-    DO_TEST("hyperv", NONE);
>-    DO_TEST("hyperv-off", NONE);
>-    DO_TEST("hyperv-panic", NONE);

This would remove the coverage of the syntax for old QEMUs.
Either leave this as-is and add the new feature in a separate test,
or you can branch the test based on QEMU versions like we do for other
features:

    DO_TEST_CAPS_VER("pv-spinlock-disabled", "2.7.0");
    DO_TEST_CAPS_VER("pv-spinlock-disabled", "4.0.0");
    DO_TEST_CAPS_LATEST("pv-spinlock-disabled");

(After 2.7.0 we stopped using +|-feature in favor of feature=on|off,
 and 4.0.0 is the last one where we use underscores)

Jano

>+    DO_TEST("hyperv", QEMU_CAPS_CANONICAL_CPU_FEATURES);
>+    DO_TEST("hyperv-off", QEMU_CAPS_CANONICAL_CPU_FEATURES);
>+    DO_TEST("hyperv-panic", QEMU_CAPS_CANONICAL_CPU_FEATURES);
>
>     DO_TEST("kvm-features", NONE);
>     DO_TEST("kvm-features-off", NONE);
>
>-- 
>Vitaly
>
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Ján Tomko <jtomko@redhat.com> writes:

> Either leave this as-is and add the new feature in a separate test,
> or you can branch the test based on QEMU versions like we do for other
> features:
>
>     DO_TEST_CAPS_VER("pv-spinlock-disabled", "2.7.0");
>     DO_TEST_CAPS_VER("pv-spinlock-disabled", "4.0.0");
>     DO_TEST_CAPS_LATEST("pv-spinlock-disabled");

I think I slightly prefer a new test: this way we can test both 

 <stimer state='on'/>

 and

 <stimer state='on'>
   <direct state='on'/>
 </stimer>

(and it makes no sense to test hv-stimer-direct for old QEMU versions
and 4.1 is "the latest" atm).

Thank you for your review, v4 is comming soon (I promise)!

-- 
Vitaly

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