On Fri, Jan 7, 2022 at 5:06 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
> > ---
> > 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.
>
No specific reason for creating a macro as such. I can remove it if it
feels noisy.
> > +
> > 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) {
> ...
> }
>
Not sure if I understood the solution..
> > + kvm->vm_started = true;
> > + mutex_unlock(&kvm->lock);
>
> Lastly, why is this in generic KVM?
>
The v1 of the series originally had it in the arm specific code.
However, I was suggested to move it to the generic code since the book
keeping is not arch specific and could be helpful to others too [1].
Thanks for the review. I'll add your other comments as well.
Regards,
Raghavendra
[1]: https://lore.kernel.org/kvmarm/YYMKphExkqttn2w0@xxxxxxxxxx/
> > }
> > r = kvm_arch_vcpu_ioctl_run(vcpu);
> > trace_kvm_userspace_exit(vcpu->run->exit_reason, r);
> > --
> > 2.34.1.448.ga2b2bfdf31-goog
> >
> > _______________________________________________
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> > kvmarm@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
