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Linux 4.15> does not allow mmap with a large address #10
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Thanks for the update. We are currently testing a new detector that uses the safer pagemap interface instead of using /dev/mem. The new detector can be found in the repository: mc-mapping-pagemap.c. The following is the result of the new detector on the Nehalem platform we used in the original PALLOC paper, which clearly shows bit 12,13,19,20 are used for the mapping. We plan to remove the old /dev/mem version in the future. $ sudo chrt -f 1 ./mc-mapping-pagemap -p 0.7 -n 3 |
Hi, thanks for the information. the new detector does not seem working well in my environment. I can provide further information if it would help improving the detector. The machine has only 1 DIMM and I set I guess memory accesses generated by
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For what it's worth, here are my results on an i7-6700HQ with two R2x8 DDR4 DIMMs (each with 16 banks and 4 bank groups):
I'm not sure how to interpret the results: the latencies for almost all bits seem way to low to reflect misses to main memory. Note that Skylake has a hashed L3, so you can't rely on simple ways/sets logic to force misses by overloading a way: you would need to know the hashing function (it has been reverse engineered elsewhere). |
Maybe related to #9 but a different issue.
Since linux 4.15,
mmap
checks if the addresses given as parameters are not harmful in the sense that they do not intentionally set flag bits embedded in the addresses (such as NX bit-related ones).https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/arch/x86/mm/mmap.c?h=v4.15.8&id=be62a32044061cb4a3b70a10598e093f1319102e
Due to this change,
mc-mapping
with the-x
option does not work for linux 4.15> because0x1000000080000000
used as theoffset
parameter ofmmap
is condemned by this check and themmap
returnsEINVAL
.The text was updated successfully, but these errors were encountered: