125 lines
4.6 KiB
Text
125 lines
4.6 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-EN-16:07.ipi Errata Notice
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The FreeBSD Project
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Topic: Excessive latency in x86 IPI delivery
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Category: core
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Module: kernel
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Announced: 2016-05-04
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Credits: Stanislav Sedov
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Affects: FreeBSD 10.2 and 10.3
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Corrected: 2016-04-27 19:12:49 UTC (stable/10, 10.3-STABLE)
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2016-05-04 15:25:47 UTC (releng/10.3, 10.3-RELEASE-p2)
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2016-05-04 15:26:23 UTC (releng/10.2, 10.2-RELEASE-p16)
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For general information regarding FreeBSD Errata Notices and Security
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Advisories, including descriptions of the fields above, security branches,
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and the following sections, please visit
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<URL:https://security.freebsd.org/>.
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I. Background
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Each CPU in an x86 system contains an interrupt controller (local APIC)
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used to handle both external interrupts and inter-processor-interrupts
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(IPIs).
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II. Problem Description
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In xAPIC mode, the local APIC can only queue a single IPI at a time. If
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a previously queued IPI is still pending when a CPU attempts to send an
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IPI, it spins waiting for the previous IPI to complete. A change merged
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prior to 10.2-RELEASE altered this loop to check the state of the previous
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IPI once every 5 microseconds rather than constantly polling.
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III. Impact
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Checking the status of the previous IPI once every 5 microseconds could
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introduce 5 microsecond delays when sending IPIs. This could increase the
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latency of various scheduling operations reducing performance.
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IV. Workaround
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No workaround is available, but non-x86 systems are not affected.
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V. Solution
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Perform one of the following:
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1) Upgrade your system to a supported FreeBSD stable or release / security
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branch (releng) dated after the correction date.
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2) To update your present system via a binary patch:
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Systems running a RELEASE version of FreeBSD on the i386 or amd64
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platforms can be updated via the freebsd-update(8) utility:
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# freebsd-update fetch
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# freebsd-update install
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3) To update your present system via a source code patch:
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The following patches have been verified to apply to the applicable
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FreeBSD release branches.
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a) Download the relevant patch from the location below, and verify the
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detached PGP signature using your PGP utility.
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# fetch https://security.FreeBSD.org/patches/EN-16:07/ipi.patch
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# fetch https://security.FreeBSD.org/patches/EN-16:07/ipi.patch.asc
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# gpg --verify ipi.patch.asc
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b) Apply the patch. Execute the following commands as root:
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# cd /usr/src
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# patch < /path/to/patch
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c) Recompile your kernel as described in
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<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
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system.
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VI. Correction details
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The following list contains the correction revision numbers for each
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affected branch.
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Branch/path Revision
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- -------------------------------------------------------------------------
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stable/10/ r298715
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releng/10.2/ r299067
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releng/10.3/ r299066
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- -------------------------------------------------------------------------
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To see which files were modified by a particular revision, run the
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following command, replacing NNNNNN with the revision number, on a
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machine with Subversion installed:
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# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
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Or visit the following URL, replacing NNNNNN with the revision number:
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<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
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VII. References
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The latest revision of this Errata Notice is available at
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https://security.FreeBSD.org/advisories/FreeBSD-EN-16:07.ipi.asc
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