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mpk: restore PKRU state when a fiber resumes execution #7789

Merged
merged 3 commits into from
Feb 15, 2024
Merged

mpk: restore PKRU state when a fiber resumes execution #7789

merged 3 commits into from
Feb 15, 2024

Commits on Feb 15, 2024

  1. mpk: restore PKRU state when a fiber resumes execution 

    Previously, when a fiber was suspended, other computation could change
the PKRU state on the current CPU. This means that the fiber could be
resumed with a different PKRU state. This could be bad, resulting in
situations in which the fiber can access more memory slots than it
should or cannot even access its own memory slots.

This change saves the PKRU state prior to a fiber being suspended. When
the fiber resumes execution, that PKRU state is restored.
    @abrown
    abrown committed Feb 15, 2024
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  2. mpk: check correct PKRU switching on async suspension 

    This adds a test that alternately polls two Wasm instances in a loop.
Since the instances are async, we can set up epochs to suspend each
fiber as we iterate over a loop. Because we alternate between the two
instances, it checks that `AsyncCx::block_on` has correctly restored the
PKRU bits; otherwise we should see test failures. In the process of
writing this test I discovered bytecodealliance#7942, which can be solved separately
(it has to do with the interaction between memory images, _not_ used
here, and MPK).

prtest:full
    @abrown
    abrown committed Feb 15, 2024
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  3. fix: condition the PKRU context switches 

    Not all stores have protection keys and MPK is not always enabled. This
change checks for these conditions before context-switching the PKRU
bits.
    @abrown
    abrown committed Feb 15, 2024
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