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bhyve: Fix NVMe iovec construction for large IOs

Authored by chuck on Jun 25 2021, 3:31 PM.



The UEFI driver included with Rocky Linux 8.4 uncovered an existing bug
in the NVMe emulation's construction of iovec's.

By default, NVMe data transfer operations use a scatter-gather list in
which all entries point to a fixed size memory region. For example, if
the Memory Page Size is 4KiB, a 2MiB IO requires 512 entries. Lists
themselves are also fixed size (default is 512 entries).

Because the list size is fixed, the last entry is special. If the IO
requires more than 512 entries, the last entry in the list contains the
address of the next list of entries. But if the IO requires exactly 512
entries, the last entry points to data.

The NVMe emulation missed this logic and unconditionally treated the
last entry as a pointer to the next list. Fix is to check if the
remaining data is greater than the page size before using the last entry
as a pointer to the next list.

PR: 256422
Reported by:

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Event Timeline

chuck requested review of this revision.Jun 25 2021, 3:31 PM

This looks good to me.

This revision is now accepted and ready to land.Jun 25 2021, 3:50 PM
This revision now requires review to proceed.Jun 27 2021, 10:00 PM
This revision was not accepted when it landed; it landed in state Needs Review.Jun 27 2021, 10:23 PM
This revision was automatically updated to reflect the committed changes.