Re: [PATCH kernel] KVM: PPC: Book3S HV: Make unique debugfs nodename

[Alexey Kardashevskiy]

On 08/07/2021 03:48, Fabiano Rosas wrote:
> Alexey Kardashevskiy <aik@xxxxxxxxx> writes:
>
> > Currently it is vm-$currentpid which works as long as there is just one
> > VM per the userspace (99.99% cases) but produces a bunch
> > of "debugfs: Directory 'vm16679' with parent 'kvm' already present!"
> > when syzkaller (syscall fuzzer) is running so only one VM is present in
> > the debugfs for a given process.
> >
> > This changes the debugfs node to include the LPID which alone should be
> > system wide unique. This leaves the existing pid for the convenience of
> > matching the VM's debugfs with the running userspace process (QEMU).
> >
> > Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
>
> Reviewed-by: Fabiano Rosas <farosas@xxxxxxxxxxxxx>

thanks.

Strangely it also fixes a bunch of

BUG: unable to handle kernel NULL pointer dereference in corrupted
BUG: unable to handle kernel paging request in corrupted

I was having 3 of these for every hour of running syzkaller and not 
anymore with this patch.


> > ---
> >   arch/powerpc/kvm/book3s_hv.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> > index 1d1fcc290fca..0223ddc0eed0 100644
> > --- a/arch/powerpc/kvm/book3s_hv.c
> > +++ b/arch/powerpc/kvm/book3s_hv.c
> > @@ -5227,7 +5227,7 @@ static int kvmppc_core_init_vm_hv(struct kvm *kvm)
> >   	/*
> >   	 * Create a debugfs directory for the VM
> >   	 */
> > -	snprintf(buf, sizeof(buf), "vm%d", current->pid);
> > +	snprintf(buf, sizeof(buf), "vm%d-lp%ld", current->pid, lpid);
> >   	kvm->arch.debugfs_dir = debugfs_create_dir(buf, kvm_debugfs_dir);
> >   	kvmppc_mmu_debugfs_init(kvm);
> >   	if (radix_enabled())

--
Alexey