Messages in this thread | | | Subject | Re: [PATCH v4 2/2] s390/vfio-ap: control access to PQAP(AQIC) interception handler | From | "Jason J. Herne" <> | Date | Tue, 25 May 2021 10:07:46 -0400 |
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On 5/25/21 9:26 AM, Jason Gunthorpe wrote: > On Tue, May 25, 2021 at 09:24:59AM -0400, Jason J. Herne wrote: >> change the function pointer to point to vfio_ap_ops:handle_pqap(). When we >> unload the module we change the function pointer back to the stub. The >> updates should be atomic operations so no lock needed, right? > > No > > Jason >
Okay... Would you be willing to elaborate, please? A counter argument, or a simple explanation would be appreciated. A simple "no" does not really do much to advance the discussion :).
I'm fairly sure that a 64-bit pointer would be updated atomically. A reader of this value is either going to see value A or value B, not the high half of A and the low half of B. Maybe we also need a memory barrier to prevent stale values from being seen on another core?
-- -- Jason J. Herne (jjherne@linux.ibm.com)
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