Messages in this thread | | | Date | Sat, 8 Jan 2022 01:06:03 +0000 | From | Sean Christopherson <> | Subject | Re: [RFC PATCH v3 01/11] KVM: Capture VM start |
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On Tue, Jan 04, 2022, Raghavendra Rao Ananta wrote: > Capture the start of the KVM VM, which is basically the
Please wrap at ~75 chars.
> start of any vCPU run. This state of the VM is helpful > in the upcoming patches to prevent user-space from > configuring certain VM features after the VM has started > running.
Please provide context of how the flag will be used. I glanced at the future patches, and knowing very little about arm, I was unable to glean useful info about exactly who is being prevented from doing what.
> > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com> > --- > include/linux/kvm_host.h | 3 +++ > virt/kvm/kvm_main.c | 9 +++++++++ > 2 files changed, 12 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index c310648cc8f1..d0bd8f7a026c 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -623,6 +623,7 @@ struct kvm { > struct notifier_block pm_notifier; > #endif > char stats_id[KVM_STATS_NAME_SIZE]; > + bool vm_started; > }; > > #define kvm_err(fmt, ...) \ > @@ -1666,6 +1667,8 @@ static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu) > } > } > > +#define kvm_vm_has_started(kvm) (kvm->vm_started)
Needs parantheses around (kvm), but why bother with a macro? This is the same header that defines struct kvm.
> + > extern bool kvm_rebooting; > > extern unsigned int halt_poll_ns; > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 72c4e6b39389..962b91ac2064 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -3686,6 +3686,7 @@ static long kvm_vcpu_ioctl(struct file *filp, > int r; > struct kvm_fpu *fpu = NULL; > struct kvm_sregs *kvm_sregs = NULL; > + struct kvm *kvm = vcpu->kvm;
If you're going to bother grabbing kvm, replace the instances below that also do vcpu->kvm.
> > if (vcpu->kvm->mm != current->mm || vcpu->kvm->vm_dead) > return -EIO; > @@ -3723,6 +3724,14 @@ static long kvm_vcpu_ioctl(struct file *filp, > if (oldpid) > synchronize_rcu(); > put_pid(oldpid); > + > + /* > + * Since we land here even on the first vCPU run, > + * we can mark that the VM has started running.
Please avoid "we", "us", etc..
"vm_started" is also ambiguous. If we end up with a flag, then I would prefer a much more literal name, a la created_vcpus, e.g. ran_vcpus or something.
> + */ > + mutex_lock(&kvm->lock);
This adds unnecessary lock contention when running vCPUs. The naive solution would be: if (!kvm->vm_started) { ... }
> + kvm->vm_started = true; > + mutex_unlock(&kvm->lock);
Lastly, why is this in generic KVM?
> } > r = kvm_arch_vcpu_ioctl_run(vcpu); > trace_kvm_userspace_exit(vcpu->run->exit_reason, r); > -- > 2.34.1.448.ga2b2bfdf31-goog > > _______________________________________________ > kvmarm mailing list > kvmarm@lists.cs.columbia.edu > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
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