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

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Message-ID: <be02290c-60a0-48af-0491-61e8a6d5b7b7@ozlabs.ru>
Date:   Fri, 13 Aug 2021 19:50:04 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Paul Mackerras <paulus@...abs.org>
Cc:     linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH kernel] KVM: PPC: Book3S HV: Make unique debugfs nodename



On 07/07/2021 14:13, Alexey Kardashevskiy wrote:
> 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@...abs.ru>

Looks like this is not enough as syzkaller still manages to cause the 
error message, I need more robust approach as in 
https://lore.kernel.org/patchwork/patch/1472025/  or   alternatively 
move this debugfs stuff under the platform-independent directory, how 
about that?


> ---
>   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