On Sat, 30 Sep 2023 01:19:24 +0100
Salil Mehta <salil.me...@huawei.com> 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.
>
> 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/context in Qemu are parked.
>
> Refactor common logic so that some APIs could be reused by vCPU Hotplug code.
>
> Signed-off-by: Salil Mehta <salil.me...@huawei.com>
Hi Salil,
A few trivial things inline, plus a question about why
cpu->cpu_index can now be used but kvm_arch_vcpu_id(cpu);
was previously needed.
Thanks,
Jonathan
> ---
> accel/kvm/kvm-all.c | 63 +++++++++++++++++++++++++++++++++-----------
> include/sysemu/kvm.h | 14 ++++++++++
> 2 files changed, 61 insertions(+), 16 deletions(-)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index ff1578bb32..b8c36ba50a 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -80,7 +80,7 @@
> #endif
>
> struct KVMParkedVcpu {
> - unsigned long vcpu_id;
> + int vcpu_id;
> int kvm_fd;
> QLIST_ENTRY(KVMParkedVcpu) node;
> };
> @@ -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, int vcpu_id);
>
> static inline void kvm_resample_fd_remove(int gsi)
> {
> @@ -320,11 +321,49 @@ err:
> return ret;
> }
>
> +void kvm_park_vcpu(CPUState *cpu)
> +{
> + int vcpu_id = cpu->cpu_index;
> + struct KVMParkedVcpu *vcpu;
> +
> + vcpu = g_malloc0(sizeof(*vcpu));
> + vcpu->vcpu_id = vcpu_id;
As vcpu_id is only used here why have the local variable?
Maybe that changes in later patches, in which case ignore this.
vcpu->vcpu_id = cpu->cpu_index;
Why is kvm_arch_vcpu_id() not necessary here any more but was
before?
> + vcpu->kvm_fd = cpu->kvm_fd;
> + QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
> +}
> +
> +int kvm_create_vcpu(CPUState *cpu)
> +{
> + int vcpu_id = cpu->cpu_index;
See below. I'm not sure why it's safe not to use kvm_arch_vcpu_id()
Seems a few architectures have less than trivial implementations of
that function currently.
> + KVMState *s = kvm_state;
> + int kvm_fd;
> +
> + DPRINTF("kvm_create_vcpu\n");
> +
> + /* check if the KVM vCPU already exist but is parked */
> + kvm_fd = kvm_get_vcpu(s, vcpu_id);
> + if (kvm_fd < 0) {
> + /* vCPU not parked: create a new KVM vCPU */
> + kvm_fd = kvm_vm_ioctl(s, KVM_CREATE_VCPU, vcpu_id);
> + if (kvm_fd < 0) {
> + error_report("KVM_CREATE_VCPU IOCTL failed for vCPU %d",
> vcpu_id);
> + return kvm_fd;
> + }
> + }
> +
> + cpu->vcpu_dirty = true;
> + cpu->kvm_fd = kvm_fd;
> + cpu->kvm_state = s;
> + cpu->dirty_pages = 0;
> + cpu->throttle_us_per_full = 0;
Trivial but I would have maintained the order wrt to the code removed
below just to avoid a reviewer having to check the two bits of code
do the same thing after the reorder.
> +
> + return 0;
> +}
> +
> static int do_kvm_destroy_vcpu(CPUState *cpu)
> {
> KVMState *s = kvm_state;
> long mmap_size;
> - struct KVMParkedVcpu *vcpu = NULL;
> int ret = 0;
>
> DPRINTF("kvm_destroy_vcpu\n");
> @@ -353,10 +392,7 @@ static int do_kvm_destroy_vcpu(CPUState *cpu)
> }
> }
>
> - vcpu = g_malloc0(sizeof(*vcpu));
> - vcpu->vcpu_id = kvm_arch_vcpu_id(cpu);
> - vcpu->kvm_fd = cpu->kvm_fd;
> - QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
> + kvm_park_vcpu(cpu);
> err:
> return ret;
> }
> @@ -369,7 +405,7 @@ void kvm_destroy_vcpu(CPUState *cpu)
> }
> }
>
> -static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id)
> +static int kvm_get_vcpu(KVMState *s, int vcpu_id)
> {
> struct KVMParkedVcpu *cpu;
>
> @@ -384,7 +420,7 @@ static int kvm_get_vcpu(KVMState *s, unsigned long
> vcpu_id)
> }
> }
>
> - return kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)vcpu_id);
> + return -1;
> }
>
> int kvm_init_vcpu(CPUState *cpu, Error **errp)
> @@ -395,19 +431,14 @@ int kvm_init_vcpu(CPUState *cpu, Error **errp)
>
> trace_kvm_init_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
>
> - ret = kvm_get_vcpu(s, kvm_arch_vcpu_id(cpu));
> + ret = kvm_create_vcpu(cpu);
The switch from kvm_arch_vcpu_id(cpu) to using
int vcpu_id = cpu->cpu_index;
Seems like a functional change on some arch.
> if (ret < 0) {
> - error_setg_errno(errp, -ret, "kvm_init_vcpu: kvm_get_vcpu failed
> (%lu)",
> + error_setg_errno(errp, -ret,
> + "kvm_init_vcpu: kvm_create_vcpu failed (%lu)",
The rewrap of the lines above seems like an unrelated change.
> kvm_arch_vcpu_id(cpu));
> goto err;
> }
>
> - cpu->kvm_fd = ret;
> - cpu->kvm_state = s;
> - cpu->vcpu_dirty = true;
> - cpu->dirty_pages = 0;
> - cpu->throttle_us_per_full = 0;
> -
> mmap_size = kvm_ioctl(s, KVM_GET_VCPU_MMAP_SIZE, 0);
> if (mmap_size < 0) {
> ret = mmap_size;
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index ee9025f8e9..785f3ed083 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -464,6 +464,20 @@ void kvm_set_sigmask_len(KVMState *s, unsigned int
> sigmask_len);
>
> int kvm_physical_memory_addr_from_host(KVMState *s, void *ram_addr,
> hwaddr *phys_addr);
> +/**
> + * kvm_create_vcpu - Gets a parked KVM vCPU or creates a KVM vCPU
> + * @cpu: QOM CPUState object for which KVM vCPU has to be created/fetched.
Extra space before QOM (same below)
> + *
> + * @returns: 0 when success, errno (<0) when failed.
> + */
> +int kvm_create_vcpu(CPUState *cpu);
Blank line here perhaps.
> +/**
> + * kvm_park_vcpu - Gets a parked KVM vCPU if it exists
> + * @cpu: QOM CPUState object for which parked KVM vCPU has to be fetched.
We aren't returning anything, so why fetch?
> + *
> + * @returns: kvm_fd (>0) when success, -1 when failed.
> + */
> +void kvm_park_vcpu(CPUState *cpu);
>
> #endif /* NEED_CPU_H */
>
