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Re: [PATCH V2 01/10] accel/kvm: Extract common KVM vCPU {creation,parkin
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From: |
Gavin Shan |
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Subject: |
Re: [PATCH V2 01/10] accel/kvm: Extract common KVM vCPU {creation,parking} code |
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Date: |
Tue, 3 Oct 2023 09:17:41 +1000 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 |
On 9/30/23 10:19, 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.
^^^^^^^^^^^^^^^^^^^
thread is spawned.
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.mehta@huawei.com>
---
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;
@vcpu_id represents the vCPU index (CPUState::cpu_index) instead of the
architectural CPU ID any more. However, I don't understand how it works
for x86, and more comments regarding it can be seen below.
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;
+ vcpu->kvm_fd = cpu->kvm_fd;
+ QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
+}
+
@vcpu_id can be dropped as suggested previously.
vcpu->vcpu_id = cpu->cpu_index;
+int kvm_create_vcpu(CPUState *cpu)
+{
+ int vcpu_id = cpu->cpu_index;
+ 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;
+
+ return 0;
+}
+
The comments here can be dropped since the code is self-explaining.
@vcpu_id represents vCPU index, instead of the architecrual vCPU ID any more.
@vcpu_id is passed to host through ioctl(KVM_CREATE_VCPU), which is expected
as an architecrual vCPU ID instead of a vCPU index by host. It's indicated
by 'struct kvm_vcpu' as below.
struct kvm_vcpu {
:
int vcpu_id; /* id given by userspace at creation */
int vcpu_idx; /* index into kvm->vcpu_array */
};
Function kvm_arch_vcpu_id() converts the vCPU instance or vCPU index to
the architecrual vCPU ID. All architectures except x86 simply returns
vCPU index (CPUState::cpu_index) as the architecrural vCPU ID. x86 returns
the APIC ID. Treating them equally seems to break x86.
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;
}
Why we have -1 here. -ENOENT seems more descriptive?
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);
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/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.
+ *
+ * @returns: 0 when success, errno (<0) when failed.
+ */
+int kvm_create_vcpu(CPUState *cpu);
+/**
+ * kvm_park_vcpu - Gets a parked KVM vCPU if it exists
+ * @cpu: QOM CPUState object for which parked KVM vCPU has to be fetched.
+ *
+ * @returns: kvm_fd (>0) when success, -1 when failed.
+ */
+void kvm_park_vcpu(CPUState *cpu);
#endif /* NEED_CPU_H */
Thanks,
Gavin