KVM Lock Overview
cpus_read_lock
@[
cpus_read_lock+5
static_key_enable+18
mem_cgroup_css_online+182
cgroup_apply_control_enable+863
cgroup_mkdir+1083
kernfs_iop_mkdir+101
vfs_mkdir+379
do_mkdirat+152
__x64_sys_mkdir+43
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 1
@[
cpus_read_lock+5
static_key_slow_inc+18
mem_cgroup_css_alloc+1310
cgroup_apply_control_enable+281
cgroup_mkdir+1083
kernfs_iop_mkdir+101
vfs_mkdir+379
do_mkdirat+152
__x64_sys_mkdir+43
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 1
@[
cpus_read_lock+5
static_key_slow_inc+18
mem_cgroup_css_alloc+1281
cgroup_apply_control_enable+281
cgroup_mkdir+1083
kernfs_iop_mkdir+101
vfs_mkdir+379
do_mkdirat+152
__x64_sys_mkdir+43
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 1
@[
cpus_read_lock+5
jump_label_update_timeout+22
process_scheduled_works+444
worker_thread+712
kthread+248
ret_from_fork+55
ret_from_fork_asm+26
]: 2
@[
cpus_read_lock+5
kvm_dev_ioctl+1214
__se_sys_ioctl+115
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 2
@[
cpus_read_lock+5
static_key_slow_inc+18
kvm_dev_ioctl+2315
__se_sys_ioctl+115
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 2
@[
cpus_read_lock+5
cgroup_procs_write_start+109
__cgroup_procs_write+87
cgroup_procs_write+23
kernfs_fop_write_iter+240
vfs_write+892
ksys_write+114
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 2
@[
cpus_read_lock+5
static_key_slow_inc+18
cgroup_bpf_attach+1210
cgroup_bpf_prog_attach+146
bpf_prog_attach+446
__sys_bpf+417
__x64_sys_bpf+28
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 2
@[
cpus_read_lock+5
cgroup_attach_lock+17
cgroup_attach_task_all+47
kvm_vm_worker_thread+70
kthread+248
ret_from_fork+55
ret_from_fork_asm+26
]: 2
@[
cpus_read_lock+5
static_key_disable+18
once_deferred+30
process_scheduled_works+444
worker_thread+712
kthread+248
ret_from_fork+55
ret_from_fork_asm+26
]: 2
@[
cpus_read_lock+5
static_key_slow_inc+18
kvm_lapic_reg_write+752
vmx_set_msr+2684
__kvm_set_msr+183
kvm_emulate_wrmsr+84
vmx_handle_exit+1205
kvm_arch_vcpu_ioctl_run+6873
kvm_vcpu_ioctl+1537
__se_sys_ioctl+115
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 2
@[
cpus_read_lock+5
static_key_slow_inc+18
kvm_create_lapic+239
kvm_arch_vcpu_create+116
kvm_vm_ioctl_create_vcpu+348
kvm_vm_ioctl+1770
__se_sys_ioctl+115
do_syscall_64+237
entry_SYSCALL_64_after_hwframe+119
]: 6
@[
cpus_read_lock+5
vmstat_shepherd+19
process_scheduled_works+444
worker_thread+712
kthread+248
ret_from_fork+55
ret_from_fork_asm+26
]: 9
kvm_lock
/*
* Ordering of locks:
*
* kvm->lock --> kvm->slots_lock --> kvm->irq_lock
*/
DEFINE_MUTEX(kvm_lock);
好多文档都没有记录
struct srcu_struct srcu;
struct srcu_struct irq_srcu;
如何保护 memslot 的
``kvm->srcu``
^^^^^^^^^^^^^
:Type: srcu lock
:Arch: any
:Protects: - kvm->memslots
- kvm->buses
:Comment: The srcu read lock must be held while accessing memslots (e.g.
when using gfn_to_* functions) and while accessing in-kernel
MMIO/PIO address->device structure mapping (kvm->buses).
The srcu index can be stored in kvm_vcpu->srcu_idx per vcpu
if it is needed by multiple functions.
例如
/*
* Called within kvm->srcu read side.
* Returns 1 to let vcpu_run() continue the guest execution loop without
* exiting to the userspace. Otherwise, the value will be returned to the
* userspace.
*/
static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
vcpu_enter_guest 还同时被 vcpu rscu 保护的，具体在 kvm_arch_vcpu_ioctl_run 中
kvm_vcpu_srcu_read_lock(vcpu);
kvm_vcpu_srcu_read_unlock(vcpu);
这个东西的实现，看似是
static inline void kvm_vcpu_srcu_read_lock(struct kvm_vcpu *vcpu)
{
#ifdef CONFIG_PROVE_RCU
WARN_ONCE(vcpu->srcu_depth++,
"KVM: Illegal vCPU srcu_idx LOCK, depth=%d", vcpu->srcu_depth - 1);
#endif
vcpu->____srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
}
synchronize_srcu(&kvm->srcu);
更多时候:
idx = srcu_read_lock(&vcpu->kvm->srcu);
如果一直在运行，会有导致始终无法释放吗? 就是这个 CPU 总是运行的状态
具体的问题在: kvm_set_memslot
page fault
mm/shmem.c:shmem_fault
启动 qemu 测试，memory backend 是 memfd ，结果为:
[52966.163244] 3 locks held by qemu-system-x86/5090:
[52966.163796] #0: ffff888127c000b0 (&vcpu->mutex){+.+.}-{4:4}, at: kvm_vcpu_ioctl+0x96/0xa70 [kvm]
[52966.164979] #1: ffffc900023e6ef0 (&kvm->srcu){.+.+}-{0:0}, at: kvm_arch_vcpu_ioctl_run+0x1379/0x2450 [kvm]
[52966.166577] #2: ffff88810864ea50 (&mm->mmap_lock){++++}-{4:4}, at: get_user_pages_unlocked+0x88/0x360
- kvm_vcpu_ioctl
if (mutex_lock_killable(&vcpu->mutex)) - kvm_arch_vcpu_ioctl_run
kvm_vcpu_srcu_read_lock(vcpu); - get_user_pages_unlocked -> __get_user_pages_locked
if (!*locked) {
if (mmap_read_lock_killable(mm))
return -EAGAIN;
must_unlock = true;
*locked = 1;
}
kvm_tdp 到底解决了什么锁
既然是一个 option ，显然可以测试出来这个东西
kvm 为什么需要 srcu 来着?
kvm_vcpu_srcu_read_unlock(vcpu);
if (vcpu->arch.mp_state == KVM_MP_STATE_HALTED)
kvm_vcpu_haltevcpu);
else
kvm_vcpu_block(vcpu);
kvm_vcpu_srcu_read_lock(vcpu);
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