Re: [PATCH kernel] KVM: PPC: Book3S: Merge powerpc's debugfs entry content into generic entry

[Fabiano Rosas <farosas@linux.ibm.com>]

Alexey Kardashevskiy <aik@ozlabs.ru> writes:

> At the moment the generic KVM code creates an "%pid-%fd" entry per a KVM
> instance; and the PPC HV KVM creates its own at "vm%pid".
>
> The rproblems with the PPC entries are:
> 1. they do not allow multiple VMs in the same process (which is extremely
> rare case mostly used by syzkaller fuzzer);
> 2. prone to race bugs like the generic KVM code had fixed in
> commit 85cd39af14f4 ("KVM: Do not leak memory for duplicate debugfs
> directories").
>
> This defines kvm_arch_create_kvm_debugfs() similar to one for vcpus.

I think kvm_arch_create_vm_debugfs is a bit mode accurate?
                        ^
> This defines 2 hooks in kvmppc_ops for allowing specific KVM
> implementations to add necessary entries.
>
> This makes use of already existing kvm_arch_create_vcpu_debugfs.
>
> This removes no more used debugfs_dir pointers from PPC kvm_arch structs.
>
> Suggested-by: Fabiano Rosas <farosas@linux.ibm.com>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

...

> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index c8f12b056968..325b388c725a 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -2771,19 +2771,14 @@ static const struct file_operations debugfs_timings_ops = {
>  };
>  
>  /* Create a debugfs directory for the vcpu */
> -static void debugfs_vcpu_init(struct kvm_vcpu *vcpu, unsigned int id)
> +static void kvmppc_arch_create_vcpu_debugfs_hv(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry)

This could lose the 'arch' since it is already inside our code and
accessed only via ops. I see that we already have a
kvmppc_create_vcpu_debugfs that's used for some BookE processor, this
would make:

kvmppc_create_vcpu_debugfs
kvmppc_create_vcpu_debugfs_hv
kvmppc_create_vcpu_debugfs_pr (possibly)

which perhaps is more consistent.

>  {
> -	char buf[16];
> -	struct kvm *kvm = vcpu->kvm;
> -
> -	snprintf(buf, sizeof(buf), "vcpu%u", id);
> -	vcpu->arch.debugfs_dir = debugfs_create_dir(buf, kvm->arch.debugfs_dir);
> -	debugfs_create_file("timings", 0444, vcpu->arch.debugfs_dir, vcpu,
> +	debugfs_create_file("timings", 0444, debugfs_dentry, vcpu,
>  			    &debugfs_timings_ops);
>  }
>  
>  #else /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */
> -static void debugfs_vcpu_init(struct kvm_vcpu *vcpu, unsigned int id)
> +static void kvmppc_arch_create_vcpu_debugfs_hv(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry)
>  {
>  }
>  #endif /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */