Hi Gavin,
> From: Gavin Shan <gs...@redhat.com>
> Sent: Wednesday, September 27, 2023 7:52 AM
> To: Salil Mehta <salil.me...@huawei.com>; qemu-devel@nongnu.org; qemu-
> a...@nongnu.org
> Cc: m...@kernel.org; jean-phili...@linaro.org; Jonathan Cameron
> <jonathan.came...@huawei.com>; lpieral...@kernel.org;
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> il...@os.amperecomputing.com; vis...@os.amperecomputing.com;
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> zhukeqian <zhukeqi...@huawei.com>; wangxiongfeng (C)
> <wangxiongfe...@huawei.com>; wangyanan (Y) <wangyana...@huawei.com>;
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> Subject: Re: [PATCH RFC V2 05/37] accel/kvm: Extract common KVM vCPU
> {creation,parking} code
>
> Hi Salil,
>
> On 9/26/23 20:04, Salil Mehta wrote:
> > KVM vCPU creation is done once during the initialization of the VM when Qemu
> > threads are spawned. This is common to all the architectures. If the
> > architecture
> > supports vCPU hot-{un}plug then this KVM vCPU creation could be deferred to
> > later point as well. Some architectures might in any case create KVM vCPUs
> > for
> > the yet-to-be plugged vCPUs (i.e. QoM Object & thread does not exists)
> > during VM
> > init time and park them.
> >
> > Hot-unplug of vCPU results in destruction of the vCPU objects in QOM but
> > the KVM vCPU objects in the Host KVM are not destroyed and their
> > representative
> > KVM vCPU objects in Qemu are parked.
> >
> > Signed-off-by: Salil Mehta <salil.me...@huawei.com>
> > ---
> > accel/kvm/kvm-all.c | 61 ++++++++++++++++++++++++++++++++++----------
> > include/sysemu/kvm.h | 2 ++
> > 2 files changed, 49 insertions(+), 14 deletions(-)
> >
>
> The most important point seems missed in the commit log: The KVM vCPU objects,
> including those hotpluggable objects, need to be in place before in-host GICv3
> is initialized. So we need expose kvm_create_vcpu() to make those KVM vCPU
> objects in place, even for those non-present vCPUs.
This is a patch common to all architectures. The point you are making is
specific
to the ARM architecture. This patch is now part of the common patch-set. Here,
https://lore.kernel.org/qemu-devel/20230930001933.2660-1-salil.me...@huawei.com/
>
> > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> > index 7b3da8dc3a..86e9c9ea60 100644
> > --- a/accel/kvm/kvm-all.c
> > +++ b/accel/kvm/kvm-all.c
> > @@ -137,6 +137,7 @@ static QemuMutex kml_slots_lock;
> > #define kvm_slots_unlock() qemu_mutex_unlock(&kml_slots_lock)
> >
> > static void kvm_slot_init_dirty_bitmap(KVMSlot *mem);
> > +static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id);
> >
> > static inline void kvm_resample_fd_remove(int gsi)
> > {
> > @@ -320,11 +321,51 @@ err:
> > return ret;
> > }
> >
> > +void kvm_park_vcpu(CPUState *cpu)
> > +{
> > + unsigned long vcpu_id = cpu->cpu_index;
> > + struct KVMParkedVcpu *vcpu;
> > +
> > + vcpu = g_malloc0(sizeof(*vcpu));
> > + vcpu->vcpu_id = vcpu_id;
>
> vcpu->vcpu_id = cpu->cpu_index;
>
> @vcpu_id can be dropped.
Yes, agreed.
Thanks
Salil.
>
> > + vcpu->kvm_fd = cpu->kvm_fd;
> > + QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
> > +}
> > +
> > +int kvm_create_vcpu(CPUState *cpu)
> > +{
> > + unsigned long vcpu_id = cpu->cpu_index;
> > + KVMState *s = kvm_state;
> > + int ret;
> > +
> > + DPRINTF("kvm_create_vcpu\n");
> > +
> > + /* check if the KVM vCPU already exist but is parked */
> > + ret = kvm_get_vcpu(s, kvm_arch_vcpu_id(cpu));
> > + if (ret > 0) {
> > + goto found;
> > + }
> > +
> > + /* create a new KVM vcpu */
> > + ret = kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)vcpu_id);
> > + if (ret < 0) {
> > + return ret;
> > + }
> > +
> > +found:
> > + cpu->vcpu_dirty = true;
> > + cpu->kvm_fd = ret;
> > + cpu->kvm_state = s;
> > + cpu->dirty_pages = 0;
> > + cpu->throttle_us_per_full = 0;
> > +
> > + return 0;
> > +}
> > +
>
> The found tag can be dropped. @cpu can be initialized if vCPU fd is found
> and then bail early.
Yes, This patch has been refactored and found has been dropped.
https://lore.kernel.org/qemu-devel/20230930001933.2660-1-salil.me...@huawei.com/
Thanks
Salil.
