Messages in this thread |  | | From | Liam Howlett <> | | Subject | Re: [PATCH] mm/mprotect: Fix maple tree start address in do_mprotect_pkey() | | Date | Fri, 26 Aug 2022 03:27:34 +0000 |
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* Andrew Morton <akpm@linux-foundation.org> [220825 21:06]: > On Thu, 25 Aug 2022 20:30:24 +0000 Liam Howlett <liam.howlett@oracle.com> wrote: > > > Use the untagged_addr() instead of the address passed into the function. > > What are the runtime effects of this fix?
Prior to my change to use the maple tree, the start address was changed before calling find_vma() with the untagged_addr() version of start. My first change recorded the tagged address and searched on the incorrect start location - which would have found the incorrect VMA. This fix will use the untagged_addr() as the start of the search as it was before I changed the code at all.
Any penalty of calling untagged_addr() occurred regardless of the version that was used. The search of the maple tree would have also occurred in both versions - just at the wrong location before this fix. I expect that the execution time would be equal as the search on the tagged address would have either returned a VMA at start, or the VMA in the next slot in the maple tree node - probably immeasurably slower since the data is very likely already in the CPU cache, but I don't have hard data to say either way. I can look into a benchmark to measure the difference between both working versions, but I don't have an arm64 native target so it will be emulated.
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