Messages in this thread | | | Subject | Re: [PATCH v4 2/2] s390/vfio-ap: control access to PQAP(AQIC) interception handler | From | Tony Krowiak <> | Date | Tue, 25 May 2021 11:08:22 -0400 |
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On 5/25/21 9:19 AM, Jason Gunthorpe wrote: > On Tue, May 25, 2021 at 09:16:30AM -0400, Tony Krowiak wrote: >> >> On 5/24/21 10:37 AM, Jason J. Herne wrote: >>> On 5/21/21 3:36 PM, Tony Krowiak wrote: >>>> The function pointer to the handler that processes interception of the >>>> PQAP instruction is contained in the mdev. If the mdev is removed and >>>> its storage de-allocated during the processing of the PQAP instruction, >>>> the function pointer could get wiped out before the function is called >>>> because there is currently nothing that controls access to it. >>>> >>>> This patch introduces two new functions: >>>> * The kvm_arch_crypto_register_hook() function registers a function >>>> pointer >>>> for processing intercepted crypto instructions. >>>> * The kvm_arch_crypto_register_hook() function un-registers a function >>>> pointer that was previously registered. >>> Typo: You meant kvm_arch_crypto_UNregister_hook() in the second bullet. >>> >>> >>> Just one overall observation on this one. The whole hook system seems >>> kind of over-engineered if this is our only use for it. It looks like a >>> kvm_s390_crypto_hook is meant to link a specific module with a function >>> pointer. Do we really need this concept? >>> >>> I think a simpler design could be to just place a mutex and a function >>> pointer in the kvm_s390_crypto struct. Then you can grab the mutex in >>> vfio_ap_ops.c when registering/unregistering. You would also grab the >>> mutex in priv.c when calling the function pointer. What I am suggesting >>> is essentially the exact same scheme you have implemented here, but >>> simpler and with less infrastructure. >> That would be great, however; when I implemented something similar, it >> resulted in a >> lockdep splat between the lock used to protect the hook and the >> matrix_dev->lock used to >> protect updates to matrix_mdev (including the freeing thereof). After >> pulling what little hair >> I have left out, this seemed like a reasonable solution, over-engineered >> though it may be. >> If somebody has a simpler solution, I'm all ears. > Why can't you put the locks in the right order? It looked trivial, I'm confused.
Because the handle_pqap() function in priv.c does not have access to the matrix_dev lock.
> > Jason
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