Messages in this thread | | | Date | Thu, 18 Jun 2009 18:20:44 +1000 | From | Paul Mackerras <> | Subject | Accessing user memory from NMI |
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What was the conclusion you guys came to about doing a user stack backtrace in an NMI handler? Are you going to access user memory directly or are you going to use the __fast_get_user_pages approach?
Ben H and I were talking today about what we'd need in order to be able to read user memory in a PMU interrupt handler. It looks like we could read user memory directly with a bit of care, on 64-bit at least. Because of the MMU hash table that would almost always work provided the page has already been touched (which stack pages would have been), but there is a small chance that the access might fail even if the address has a valid PTE. At that point we could fall back to the __fast_get_user_pages method, but I'm not sure it's worth it.
Paul.
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