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Re: [Qemu-devel] [PATCH v6 15/17] target-s390x: Extend arch specific QMP
From: |
Michael Mueller |
Subject: |
Re: [Qemu-devel] [PATCH v6 15/17] target-s390x: Extend arch specific QMP command query-cpu-definitions |
Date: |
Wed, 6 May 2015 17:31:06 +0200 |
On Tue, 5 May 2015 15:40:34 -0300
Eduardo Habkost <address@hidden> wrote:
> On Mon, Apr 27, 2015 at 04:53:29PM +0200, Michael Mueller wrote:
> [...]
> > diff --git a/target-s390x/kvm.c b/target-s390x/kvm.c
> > index 4d75ff0..94fede5 100644
> > --- a/target-s390x/kvm.c
> > +++ b/target-s390x/kvm.c
> > @@ -276,12 +276,59 @@ static int cpu_model_set(KVMState *s, uint64_t attr,
> > void *addr)
> > return rc;
> > }
> >
> > -static int kvm_s390_get_machine_props(KVMState *s, S390MachineProps *prop)
>
> This seems to duplicate lots of the existing KVM code. (See additional
> comment below about possible ways to avoid it).
some :-)
>
> > +static int get_machine_props_fallback(S390MachineProps *prop)
> > +{
> > + struct kvm_device_attr dev_attr;
> > + int rc, kvmfd = -1, vmfd = -1;
> > +
> > + rc = qemu_open("/dev/kvm", O_RDWR);
> > + if (rc < 0) {
> > + goto out_err;
> > + }
> > + kvmfd = rc;
> > +
> > + rc = ioctl(kvmfd, KVM_CREATE_VM, 0);
> > + if (rc < 0) {
> > + goto out_err;
> > + }
> > + vmfd = rc;
> > +
> > + rc = ioctl(vmfd, KVM_CHECK_EXTENSION, KVM_CAP_VM_ATTRIBUTES);
> > + if (rc < 0) {
> > + rc = -ENOSYS;
> > + goto out_err;
> > + }
> > +
> > + dev_attr.group = KVM_S390_VM_CPU_MODEL;
> > + dev_attr.attr = KVM_S390_VM_CPU_MACHINE;
> > + rc = ioctl(vmfd, KVM_HAS_DEVICE_ATTR, &dev_attr);
> > + if (rc < 0) {
> > + rc = -EFAULT;
> > + goto out_err;
> > + }
> > +
> > + dev_attr.addr = (uint64_t) prop;
> > + rc = ioctl(vmfd, KVM_GET_DEVICE_ATTR, &dev_attr);
> > +
> > +out_err:
> > + if (vmfd >= 0) {
> > + close(vmfd);
> > + }
> > + if (kvmfd >= 0) {
> > + close(kvmfd);
> > + }
> > +
> > + return rc;
> > +}
> > +
> > +int kvm_s390_get_machine_props(KVMState *s, S390MachineProps *prop)
> > {
> > int rc = -EFAULT;
> >
> > if (s) {
> > rc = cpu_model_get(s, KVM_S390_VM_CPU_MACHINE, prop);
> > + } else {
> > + rc = get_machine_props_fallback(prop);
> > }
>
> The comments below are just suggestions, not something which should
> block the patch, in my opinion:
>
> First, if s is always NULL inside arch_query_cpu_definitions(), and is
> always non-NULL inside kvm_setup_cpu_classes(), why don't you just call
> keep the original kvm_s390_get_machine_props() function, and call and
> get_machine_props_fallback() inside arch_query_cpu_definitions()?
My reason for pulling both paths through the same internal interface call is
to have just single call for the same purpose.
>
> The only thing common to both cases is the tracing point, but if we are
> running two completely different code paths I assume it would be a good
> thing to have a different tracing point for
> get_machine_props_fallback().
>
>
> Second, you shouldn't even need to duplicate code in
> get_machine_props_fallback() if you are able to create an accel object
> and do just basic initialization so that cpu_model_get() works.
> Allowing accel objects to be created on the fly was one of the main
> purposes of the accel QOM work.
>
> For example, if we do something like this:
>
> https://github.com/ehabkost/qemu-hacks/commit/36a250e34c5fd0d43a25271f5bc9b04681fdd56a
> [1]
> https://github.com/ehabkost/qemu-hacks/commits/work/accel-open-func
I had a look at your qemu-hacks before writing the _fallback() routine
but did not wanted to base on some not yet published code. Once your part goes
upstream my intend is to provide a cleanup patch... And I was missing the
KVM_CREATE_VM actually.
>
> Then the code could look like this:
>
> accel.c:
>
> /* configure_accelerator() would be changed to reuse this function: */
> AccelState *accel_create(const char *accel_name)
> {
> AccelClass *acc = accel_find(accel_name);
> /*TODO: error handling, checking acc->available() */
> return ACCEL(object_new(object_class_get_name(OBJECT_CLASS(acc))));
> }
>
> /* Do basic accel initialization without affecting global QEMU state */
> /* accel_init_machine() would be changed to reuse this function: */
> void accel_open(AccelState *s, Error **errp)
> {
> object_property_set_bool(OBJECT(s), true, "open", errp);
> }
>
> target-s390/kvm.c:
>
> /* Using a different function name would be interesting, as it would be
> * the main arch_query_cpu_definitions() code path, not a fallback.
> */
> int get_machine_props_fallback(S390MachineProps *prop)
> {
> int r;
> AccelState *ac = accel_create("kvm");
> /*TODO: error handling */
> accel_open(ac, &err);
> r = cpu_model_get(ac, prop);
> object_unref(OBJECT(ac));
> return r;
> }
>
>
> [1] I only moved the /dev/kvm opening to the open method, but maybe the
> whole code up to KVM_CREATE_VM and capabitlity checking could be
> moved.
Yes as mentioned above.
> (But I don't know how to handle kvm_type, as it is currently
> provided by MachineClass. Maybe kvm_type() belongs to CPUClass
> instead of MachineClass?)
>
> > trace_kvm_get_machine_props(rc, prop->cpuid, prop->ibc);
> >
> > --
> > 1.8.3.1
> >
>