patches: Prefault page tables used in stacks allocated for threads #73
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We need to explicitly populate the page tables allocated for stacks (via mmap's `MAP_POPULATE` flag) in order to avoid infinite page fault loops during runtime. This measure is necessary since Unikraft on AArch64 does not switch stacks when handling CPU exceptions. A page fault occuring on the stack would cause the trap handler to save all the registers on the same stack, thus generating another page fault, ad infinitum. Signed-off-by: Eduard Vintilă <eduard.vintila47@gmail.com>
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Maaan, I gotta say I really like the commit message: "ad infinitum" 🧠 ! Very descriptive and nicely written. I really appreciate it when people put in effort in their commits 💪.
Thanks for your work! I agree this fix will work, however at a great cost! Stacks (and especially userspace stacks) can be huge (MB in size). This means that pre-populating them early on has a big impact on boot 👢 times. I am wondering 🤔, would it be possible that #1174 could solve this issue without needing to prefault the stacks (btw I have not tested it individually yet so i'd advise to use #1175 instead)?
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@mogasergiu, thank you so much for the nice comment! :) It's true, I completely agree it has a big impact on boot times - it was more of a quick fix to temporarily get the ARM64 Golang support rolling until we find a proper solution. But now your PR does a wonderful job to handle the problem described in this PR, I've just tested it and all works very smoothly 😎 Thanks a lot for the great work! Now, I hereby officially declare this PR obsolete! 🧑⚖️ |
We need to explicitly populate the page tables allocated for stacks (via mmap's
MAP_POPULATEflag) in order to avoid infinite page fault loops during runtime. This measure is necessary since Unikraft on AArch64 does not switch stacks when handling CPU exceptions. A page fault occuring on the stack would cause the trap handler to save all the registers on the same stack, thus generating another page fault, ad infinitum.This PR is part of a larger series which provides support for Golang on ARM64 platforms: