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

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Date:   Thu, 8 Jul 2021 12:22:53 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Fabiano Rosas <farosas@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org,
        Paul Mackerras <paulus@...abs.org>
Subject: Re: [PATCH kernel] KVM: PPC: Book3S HV: Make unique debugfs nodename



On 08/07/2021 03:48, Fabiano Rosas wrote:
> Alexey Kardashevskiy <aik@...abs.ru> 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@...abs.ru>
> 
> Reviewed-by: Fabiano Rosas <farosas@...ux.ibm.com>

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