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.
> +
> 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
>
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