RE: [PATCH v2 1/4] accel/kvm: Extract common KVM vCPU {creation, parking} code

[Salil Mehta]

Hi Harsh,

>  From: Harsh Prateek Bora <harshpb@linux.ibm.com>
>  Sent: Thursday, May 16, 2024 11:15 AM
>  
>  Hi Salil,
>  
>  Thanks for your email.
>  Your patch 1/8 is included here based on review comments on my previous
>  patch from one of the maintainers in the community and therefore I had
>  kept you in CC to be aware of the desire of having this independent patch to
>  get merged earlier even if your other patches in the series may go through
>  further reviews.

I really don’t know which discussion are  you pointing at? Please understand
you are fixing a bug and we are pushing a feature which has got large series.
It will break the patch-set  which is about t be merged.

There will be significant overhead of testing on us for the work we have been
carrying forward for large time. This will be disruptive. Please dont!


>  
>  I am hoping to see your v9 soon and thereafter maintainer(s) may choose to
>  pick the latest independent patch if needs to be merged earlier.


I don’t think you are understanding what problem it is causing. For your
small bug fix you are causing significant delays at our end.


Thanks
Salil.
>  
>  Thanks for your work and let's be hopeful it gets merged soon.
>  
>  regards,
>  Harsh
>  
>  On 5/16/24 14:00, Salil Mehta wrote:
>  > Hi Harsh,
>  >
>  > Thanks for your interest in the patch-set but taking away patches like
>  > this from other series without any discussion can disrupt others work
>  > and its acceptance on time. This is because we will have to put lot of
>  > effort in rebasing bigger series and then testing overhead comes along
>  > with it.
>  >
>  > The patch-set (from where this  patch has been taken) is part of even
>  > bigger series and there have been many people and companies toiling to
>  > fix the bugs collectively in that series and for years.
>  >
>  > I'm about float the V9 version of the Arch agnostic series which this
>  > patch is part of and you can rebase your patch-set from there. I'm
>  > hopeful that it will get accepted in this cycle.
>  >
>  >
>  > Many thanks
>  > Salil.
>  >
>  >>   From: Harsh Prateek Bora <harshpb@linux.ibm.com>
>  >>   Sent: Thursday, May 16, 2024 6:32 AM
>  >>
>  >>   From: Salil Mehta <salil.mehta@huawei.com>
>  >>
>  >>   KVM vCPU creation is done once during the vCPU realization when
>  Qemu
>  >>   vCPU thread is spawned. This is common to all the architectures as of
>  now.
>  >>
>  >>   Hot-unplug of vCPU results in destruction of the vCPU object in QOM
>  but
>  >>   the corresponding KVM vCPU object in the Host KVM is not destroyed
>  as
>  >>   KVM doesn't support vCPU removal. Therefore, its representative KVM
>  >>   vCPU object/context in Qemu is parked.
>  >>
>  >>   Refactor architecture common logic so that some APIs could be reused
>  by
>  >>   vCPU Hotplug code of some architectures likes ARM, Loongson etc.
>  Update
>  >>   new/old APIs with trace events instead of DPRINTF. No functional
>  change is
>  >>   intended here.
>  >>
>  >>   Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
>  >>   Reviewed-by: Gavin Shan <gshan@redhat.com>
>  >>   Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
>  >>   Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>  >>   Tested-by: Xianglai Li <lixianglai@loongson.cn>
>  >>   Tested-by: Miguel Luis <miguel.luis@oracle.com>
>  >>   Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
>  >>   [harshpb: fixed rebase failures in include/sysemu/kvm.h]
>  >>   Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
>  >>   ---
>  >>    include/sysemu/kvm.h   | 15 ++++++++++
>  >>    accel/kvm/kvm-all.c    | 64 ++++++++++++++++++++++++++++++++---
>  -----
>  >>   --
>  >>    accel/kvm/trace-events |  5 +++-
>  >>    3 files changed, 68 insertions(+), 16 deletions(-)
>  >>
>  >>   diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h index
>  >>   eaf801bc93..fa3ec74442 100644
>  >>   --- a/include/sysemu/kvm.h
>  >>   +++ b/include/sysemu/kvm.h
>  >>   @@ -434,6 +434,21 @@ 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
>  >>   fetched/created.
>  >>   + *
>  >>   + * @returns: 0 when success, errno (<0) when failed.
>  >>   + */
>  >>   +int kvm_create_vcpu(CPUState *cpu);
>  >>   +
>  >>   +/**
>  >>   + * kvm_park_vcpu - Park QEMU KVM vCPU context
>  >>   + * @cpu: QOM CPUState object for which QEMU KVM vCPU context
>  has to
>  >>   be parked.
>  >>   + *
>  >>   + * @returns: none
>  >>   + */
>  >>   +void kvm_park_vcpu(CPUState *cpu);
>  >>
>  >>    #endif /* COMPILING_PER_TARGET */
>  >>
>  >>   diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index
>  >>   d7281b93f3..30d42847de 100644
>  >>   --- a/accel/kvm/kvm-all.c
>  >>   +++ b/accel/kvm/kvm-all.c
>  >>   @@ -128,6 +128,7 @@ 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)  { @@ -340,14
>  +341,53
>  >>   @@ err:
>  >>        return ret;
>  >>    }
>  >>
>  >>   +void kvm_park_vcpu(CPUState *cpu)
>  >>   +{
>  >>   +    struct KVMParkedVcpu *vcpu;
>  >>   +
>  >>   +    trace_kvm_park_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(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); }
>  >>   +
>  >>   +int kvm_create_vcpu(CPUState *cpu)
>  >>   +{
>  >>   +    unsigned long vcpu_id = kvm_arch_vcpu_id(cpu);
>  >>   +    KVMState *s = kvm_state;
>  >>   +    int kvm_fd;
>  >>   +
>  >>   +    trace_kvm_create_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
>  >>   +
>  >>   +    /* 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 %lu",
>  >>   vcpu_id);
>  >>   +            return kvm_fd;
>  >>   +        }
>  >>   +    }
>  >>   +
>  >>   +    cpu->kvm_fd = kvm_fd;
>  >>   +    cpu->kvm_state = s;
>  >>   +    cpu->vcpu_dirty = true;
>  >>   +    cpu->dirty_pages = 0;
>  >>   +    cpu->throttle_us_per_full = 0;
>  >>   +
>  >>   +    return 0;
>  >>   +}
>  >>   +
>  >>    static int do_kvm_destroy_vcpu(CPUState *cpu)  {
>  >>        KVMState *s = kvm_state;
>  >>        long mmap_size;
>  >>   -    struct KVMParkedVcpu *vcpu = NULL;
>  >>        int ret = 0;
>  >>
>  >>   -    trace_kvm_destroy_vcpu();
>  >>   +    trace_kvm_destroy_vcpu(cpu->cpu_index,
>  kvm_arch_vcpu_id(cpu));
>  >>
>  >>        ret = kvm_arch_destroy_vcpu(cpu);
>  >>        if (ret < 0) {
>  >>   @@ -373,10 +413,7 @@ 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;
>  >>    }
>  >>   @@ -397,6 +434,8 @@ static int kvm_get_vcpu(KVMState *s, unsigned
>  long
>  >>   vcpu_id)
>  >>            if (cpu->vcpu_id == vcpu_id) {
>  >>                int kvm_fd;
>  >>
>  >>   +            trace_kvm_get_vcpu(vcpu_id);
>  >>   +
>  >>                QLIST_REMOVE(cpu, node);
>  >>                kvm_fd = cpu->kvm_fd;
>  >>                g_free(cpu);
>  >>   @@ -404,7 +443,7 @@ static int kvm_get_vcpu(KVMState *s, unsigned
>  long
>  >>   vcpu_id)
>  >>            }
>  >>        }
>  >>
>  >>   -    return kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)vcpu_id);
>  >>   +    return -ENOENT;
>  >>    }
>  >>
>  >>    int kvm_init_vcpu(CPUState *cpu, Error **errp) @@ -415,19 +454,14
>  @@
>  >>   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);
>  >>        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)",
>  >>                             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/accel/kvm/trace-events b/accel/kvm/trace-events index
>  >>   681ccb667d..75c1724e78 100644
>  >>   --- a/accel/kvm/trace-events
>  >>   +++ b/accel/kvm/trace-events
>  >>   @@ -9,6 +9,10 @@ kvm_device_ioctl(int fd, int type, void *arg) "dev fd
>  %d,
>  >>   type 0x%x, arg %p"
>  >>    kvm_failed_reg_get(uint64_t id, const char *msg) "Warning: Unable to
>  >>   retrieve ONEREG %" PRIu64 " from KVM: %s"
>  >>    kvm_failed_reg_set(uint64_t id, const char *msg) "Warning: Unable to
>  set
>  >>   ONEREG %" PRIu64 " to KVM: %s"
>  >>    kvm_init_vcpu(int cpu_index, unsigned long arch_cpu_id) "index: %d
>  id:
>  >>   %lu"
>  >>   +kvm_create_vcpu(int cpu_index, unsigned long arch_cpu_id) "index:
>  %d
>  >>   id: %lu"
>  >>   +kvm_get_vcpu(unsigned long arch_cpu_id) "id: %lu"
>  >>   +kvm_destroy_vcpu(int cpu_index, unsigned long arch_cpu_id) "index:
>  %d
>  >>   id: %lu"
>  >>   +kvm_park_vcpu(int cpu_index, unsigned long arch_cpu_id) "index: %d
>  id:
>  >>   %lu"
>  >>    kvm_irqchip_commit_routes(void) ""
>  >>    kvm_irqchip_add_msi_route(char *name, int vector, int virq) "dev %s
>  >>   vector %d virq %d"
>  >>    kvm_irqchip_update_msi_route(int virq) "Updating MSI route
>  virq=%d"
>  >>   @@ -25,7 +29,6 @@ kvm_dirty_ring_reaper(const char *s) "%s"
>  >>    kvm_dirty_ring_reap(uint64_t count, int64_t t) "reaped %"PRIu64"
>  pages
>  >>   (took %"PRIi64" us)"
>  >>    kvm_dirty_ring_reaper_kick(const char *reason) "%s"
>  >>    kvm_dirty_ring_flush(int finished) "%d"
>  >>   -kvm_destroy_vcpu(void) ""
>  >>    kvm_failed_get_vcpu_mmap_size(void) ""
>  >>    kvm_cpu_exec(void) ""
>  >>    kvm_interrupt_exit_request(void) ""
>  >>   --
>  >>   2.39.3
>  >