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

On 08/07/2021 03:48, Fabiano Rosas wrote:

Alexey Kardashevskiy [off-list ref] writes:

quoted

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 <redacted>

Reviewed-by: Fabiano Rosas <redacted>

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.

quoted

---
  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