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several caprevoke optimizations #2195

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several caprevoke optimizations #2195

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Commits on Oct 9, 2024

  1. caprevoke: Make the skip_fault optimization smarter 

    If, when scanning, we reach a VA that is unmapped and corresponds to a
non-resident page, and the VM object is swap-backed and has no swap blocks
assigned, we skip to the next resident page.

Extend this optimization to the case where the object has swap blocks assigned:
the in-memory tracking structure for a swap block includes a bitmap of all the
capability tags, so when skipping we can search for the closer of
- the next resident page
- the next page backed by a swap block that has at least one capability tag.
    @markjdb
    markjdb committed Oct 9, 2024
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  2. caprevoke: Skip VM objects that have OBJ_HASCAP clear 

    This skips over vnode mappings that have PROT_READ_CAP set in max_prot
and thus avoids a lot of needless scanning.

Add some counters so that we can see the relative effectiveness of different
checks in reducing the number of scanned virtual pages.
    @markjdb
    markjdb committed Oct 9, 2024
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  3. caprevoke: Bail if the target process exited during an async scan 

    This avoids some needless work in cases where a short-lived process triggers
async revocation.
    @markjdb
    markjdb committed Oct 9, 2024
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