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Allow flexible memory management using Uffd#515
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tyler wants to merge 28 commits intotyler/uffd-integrationfrom
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Allow flexible memory management using Uffd#515tyler wants to merge 28 commits intotyler/uffd-integrationfrom
tyler wants to merge 28 commits intotyler/uffd-integrationfrom
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…rting with entrypoint_test.
… a fork-related bug.
- Instantiates the suite in `lucet_runtime_internals::alloc::tests` for `UffdRegion - Fixes early return issues in `UffdRegion` similar to #455 - Adds a test to show that the per-instance heap limit applies to runtime expansions, not just initial instantiation - Refactors `validate_runtime_spec` to take the per-instance heap limit as an additional argument. This centralizes the logic for rejecting initially-oversized heap limits, and makes it clearer what's happening in each region's instantiation logic. - Removes the `UffdRegion`'s assertion that signal stack size is a multiple of page size. Since the user can now control this as a parameter, we reject it gracefully when validating `Limits` rather than panicking.
Leaving the question of errors in the handler alone for this commit, since that'll be a more major change.
Notably, this should get us building and running uffd in Linux CI. It turns out to be a tremendous pain to enable a feature flag for just one crate within a workspace. The situation is [being addressed][1], but in the meantime I believe the best route forward is to just have uffd on by default for Linux. [1]: rust-lang/cargo#5364
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Just a little style note, otherwise I think this looks fantastic. I'm really pleased how easily you were able to extract those bits! I guess when you're dealing with raw pointers, you don't have to worry at all about cloning or borrowing snags 🙂
Co-authored-by: Adam C. Foltzer <acfoltzer@fastly.com>
…d of a host page.
…ization works as expected.
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Cherry picked the relevant bits over to #492 |
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This adds a UffdStrategy trait to allow users of UffdRegion to configure the way faults are handled.
This will be important especially to Lucet users who have highly concurrent applications and potentially large linear memories. Uffd in its most naive form is likely to be slower than the Mmap region because of the additional work done to shunt faults back into userspace, and the reaction to those faults over to the kernel.
This can be dealt with by being smarter about how those faults are handled. For instance, work can be batched up. Instead of copying one host page per fault, one could copy a batch of them. This doesn't implement that, but does provide the facilities to make it possible.