Hi Reiji,
On Thu, Jan 6, 2022 at 10:07 PM Reiji Watanabe <reijiw@xxxxxxxxxx> wrote:
>
> Hi Raghu,
>
> On Tue, Jan 4, 2022 at 11:49 AM Raghavendra Rao Ananta
> <rananta@xxxxxxxxxx> wrote:
> >
> > Capture the start of the KVM VM, which is basically the
> > 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.
> >
> > 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;
>
> Since KVM_RUN on any vCPUs doesn't necessarily mean that the VM
> started yet, the name might be a bit misleading IMHO. I would
> think 'has_run_once' or 'ran_once' might be more clear (?).
>
I always struggle with the names; but if you feel that 'ran_once'
makes more sense for a reader, I can change it.
>
> > };
> >
> > #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)
> > +
> > 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 (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.
> > + */
>
> It might be nicer to add a comment why the code below gets kvm->lock.
>
I've been going back and forth on this one. Initially I considered
simply going with atomic_t, but the patch 4/11 (KVM: arm64: Setup a
framework for hypercall bitmap firmware registers)
kvm_arm_set_fw_reg_bmap()'s implementation felt like we need a lock to
have the whole 'is the register busy?' operation atomic. But, that's
just one of the applications.
> Anyway, the patch generally looks good to me, and thank you
> for making this change (it works for my purpose as well).
>
> Reviewed-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
>
Glad that it's helping you as well and thanks for the review.
Regards,
Raghavendra
> Thanks,
> Reiji
>
>
> > + mutex_lock(&kvm->lock);
> > + kvm->vm_started = true;
> > + mutex_unlock(&kvm->lock);
> > }
> > r = kvm_arch_vcpu_ioctl_run(vcpu);
> > trace_kvm_userspace_exit(vcpu->run->exit_reason, r);
> > --
> > 2.34.1.448.ga2b2bfdf31-goog
> >
