[PATCH 2/2] qemu: Generate command line for tb-cache feature

[Michal Privoznik]

Alright, here's the deal: to enable tb-cache one has to use
'-accel tcg,tb-size=' which then conflicts with '-machine
accel=tcg'. But sure, we can use the old -accel in this specific
case. But because of how the tb-size argument is defined in QEMU
there's no way for us to have a capability check. The feature was
introduced in QEMU commit of v5.0.0-rc0~175^2~62 and is tied to
TCG only. Therefore, I think we can live without capability
check. Worst case scenario, QEMU fails to start.

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/229
Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_command.c                       | 14 ++++++-
 ...efault-cpu-tcg-features.x86_64-latest.args | 40 +++++++++++++++++++
 tests/qemuxml2argvtest.c                      |  1 +
 3 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 tests/qemuxml2argvdata/x86_64-default-cpu-tcg-features.x86_64-latest.args

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 45278c7108..7d9cb386fd 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -7031,14 +7031,21 @@ qemuBuildMachineCommandLine(virCommand *cmd,
     virTristateSwitch smm = def->features[VIR_DOMAIN_FEATURE_SMM];
     virCPUDef *cpu = def->cpu;
     g_auto(virBuffer) buf = VIR_BUFFER_INITIALIZER;
+    unsigned long long tb_cache = 0;
     size_t i;
 
+    if (def->features[VIR_DOMAIN_FEATURE_TCG] == VIR_TRISTATE_SWITCH_ON)
+        tb_cache = def->tcg_features->tb_cache;
+
     virCommandAddArg(cmd, "-machine");
     virBufferAdd(&buf, def->os.machine, -1);
 
     switch ((virDomainVirtType)def->virtType) {
     case VIR_DOMAIN_VIRT_QEMU:
-        virBufferAddLit(&buf, ",accel=tcg");
+        /* Unfortunately, -machine doesn't accept -accel arguments and the two
+         * are mutually exclusive. Don't output accel= if we need -accel. */
+        if (tb_cache == 0)
+            virBufferAddLit(&buf, ",accel=tcg");
         break;
 
     case VIR_DOMAIN_VIRT_KVM:
@@ -7288,6 +7295,11 @@ qemuBuildMachineCommandLine(virCommand *cmd,
 
     virCommandAddArgBuffer(cmd, &buf);
 
+    if (tb_cache > 0) {
+        virCommandAddArg(cmd, "-accel");
+        virCommandAddArgFormat(cmd, "tcg,tb-size=%llu", tb_cache >> 10);
+    }
+
     return 0;
 }
 
diff --git a/tests/qemuxml2argvdata/x86_64-default-cpu-tcg-features.x86_64-latest.args b/tests/qemuxml2argvdata/x86_64-default-cpu-tcg-features.x86_64-latest.args
new file mode 100644
index 0000000000..0800ea4294
--- /dev/null
+++ b/tests/qemuxml2argvdata/x86_64-default-cpu-tcg-features.x86_64-latest.args
@@ -0,0 +1,40 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/tmp/lib/domain--1-guest \
+USER=test \
+LOGNAME=test \
+XDG_DATA_HOME=/tmp/lib/domain--1-guest/.local/share \
+XDG_CACHE_HOME=/tmp/lib/domain--1-guest/.cache \
+XDG_CONFIG_HOME=/tmp/lib/domain--1-guest/.config \
+/usr/bin/qemu-system-x86_64 \
+-name guest=guest,debug-threads=on \
+-S \
+-object '{"qom-type":"secret","id":"masterKey0","format":"raw","file":"/tmp/lib/domain--1-guest/master-key.aes"}' \
+-machine pc-q35-6.2,usb=off,dump-guest-core=off,memory-backend=pc.ram \
+-accel tcg,tb-size=100 \
+-cpu qemu64 \
+-m 4096 \
+-object '{"qom-type":"memory-backend-ram","id":"pc.ram","size":4294967296}' \
+-overcommit mem-lock=off \
+-smp 4,sockets=4,cores=1,threads=1 \
+-uuid 1ccfd97d-5eb4-478a-bbe6-88d254c16db7 \
+-display none \
+-no-user-config \
+-nodefaults \
+-chardev socket,id=charmonitor,fd=1729,server=on,wait=off \
+-mon chardev=charmonitor,id=monitor,mode=control \
+-rtc base=utc \
+-no-shutdown \
+-boot strict=on \
+-device '{"driver":"pcie-root-port","port":8,"chassis":1,"id":"pci.1","bus":"pcie.0","multifunction":true,"addr":"0x1"}' \
+-device '{"driver":"pcie-root-port","port":9,"chassis":2,"id":"pci.2","bus":"pcie.0","addr":"0x1.0x1"}' \
+-device '{"driver":"pcie-root-port","port":10,"chassis":3,"id":"pci.3","bus":"pcie.0","addr":"0x1.0x2"}' \
+-device '{"driver":"pcie-root-port","port":11,"chassis":4,"id":"pci.4","bus":"pcie.0","addr":"0x1.0x3"}' \
+-device '{"driver":"qemu-xhci","id":"usb","bus":"pci.1","addr":"0x0"}' \
+-blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/guest.qcow2","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}' \
+-blockdev '{"node-name":"libvirt-1-format","read-only":false,"driver":"qcow2","file":"libvirt-1-storage"}' \
+-device '{"driver":"virtio-blk-pci","bus":"pci.2","addr":"0x0","drive":"libvirt-1-format","id":"virtio-disk0","bootindex":1}' \
+-audiodev id=audio1,driver=none \
+-device '{"driver":"virtio-balloon-pci","id":"balloon0","bus":"pci.3","addr":"0x0"}' \
+-sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny \
+-msg timestamp=on
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 1c59395203..56ecc46071 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -3422,6 +3422,7 @@ mymain(void)
     DO_TEST_CAPS_ARCH_LATEST("x86_64-default-cpu-tcg-pc-4.2", "x86_64");
     DO_TEST_CAPS_ARCH_LATEST("x86_64-default-cpu-kvm-q35-4.2", "x86_64");
     DO_TEST_CAPS_ARCH_LATEST("x86_64-default-cpu-tcg-q35-4.2", "x86_64");
+    DO_TEST_CAPS_ARCH_LATEST("x86_64-default-cpu-tcg-features", "x86_64");
 
     DO_TEST_CAPS_LATEST("virtio-9p-multidevs");
     DO_TEST_CAPS_LATEST("virtio-9p-createmode");
-- 
2.32.0