Allow disabling of unmapped I/O on FreeBSD #12446
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We have a tunable which permits one to disable the use of unmapped I/O for the buffer cache. Respect it in ZFS as well. This is useful for KMSAN, which cannot easily maintain shadow state for unmapped pages. No functional change intended, as unmapped I/O is permitted by default and there's no real reason to disable it in practice except for debugging. Signed-off-by: Mark Johnston <markj@FreeBSD.org>
amotin
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Jul 29, 2021
ghost
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Jul 30, 2021
tonynguien
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Jul 30, 2021
behlendorf
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Aug 24, 2021
We have a tunable which permits one to disable the use of unmapped I/O for the buffer cache. Respect it in ZFS as well. This is useful for KMSAN, which cannot easily maintain shadow state for unmapped pages. No functional change intended, as unmapped I/O is permitted by default and there's no real reason to disable it in practice except for debugging. Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12446
behlendorf
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Aug 24, 2021
We have a tunable which permits one to disable the use of unmapped I/O for the buffer cache. Respect it in ZFS as well. This is useful for KMSAN, which cannot easily maintain shadow state for unmapped pages. No functional change intended, as unmapped I/O is permitted by default and there's no real reason to disable it in practice except for debugging. Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12446
behlendorf
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Aug 31, 2021
We have a tunable which permits one to disable the use of unmapped I/O for the buffer cache. Respect it in ZFS as well. This is useful for KMSAN, which cannot easily maintain shadow state for unmapped pages. No functional change intended, as unmapped I/O is permitted by default and there's no real reason to disable it in practice except for debugging. Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes #12446
tonyhutter
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Sep 15, 2021
We have a tunable which permits one to disable the use of unmapped I/O for the buffer cache. Respect it in ZFS as well. This is useful for KMSAN, which cannot easily maintain shadow state for unmapped pages. No functional change intended, as unmapped I/O is permitted by default and there's no real reason to disable it in practice except for debugging. Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12446
rincebrain
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Sep 22, 2021
We have a tunable which permits one to disable the use of unmapped I/O for the buffer cache. Respect it in ZFS as well. This is useful for KMSAN, which cannot easily maintain shadow state for unmapped pages. No functional change intended, as unmapped I/O is permitted by default and there's no real reason to disable it in practice except for debugging. Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Mark Johnston <markj@FreeBSD.org> Closes openzfs#12446
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Motivation and Context
This helps enable the use of KMSAN with ZFS on FreeBSD. This is a feature which can detect uses of uninitialized memory. Without this change, KMSAN is prone to report false positives, since with unmapped I/O it has no way of tracking initialization state.
Description
The change extends the use of
unmapped_buf_allowedto ZFS. When KMSAN is enabled,unmapped_buf_allowedis false. This tunable exists only for debugging purposes and will be set to true in production kernels.How Has This Been Tested?
Manually, running a KMSAN-enabled FreeBSD kernel with a ZFS root.
Types of changes
Checklist:
Signed-off-by.