Date: Sat, 24 Jan 2004 15:38:48 -0800 (PST) From: Stephan Uphoff <ups@tree.com> To: freebsd-gnats-submit@FreeBSD.org Subject: i386/61852: i386 pmap SMP race condition can cause lost page modification. Message-ID: <200401242338.i0ONcmfu079114@www.freebsd.org> Resent-Message-ID: <200401242340.i0ONe9ct056595@freefall.freebsd.org>
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>Number: 61852
>Category: i386
>Synopsis: i386 pmap SMP race condition can cause lost page modification.
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-i386
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sat Jan 24 15:40:08 PST 2004
>Closed-Date:
>Last-Modified:
>Originator: Stephan Uphoff
>Release: current
>Organization:
>Environment:
N/A
>Description:
The current i386 pmap does not always atomically change ptes.
( Only clearing a pte is currently atomic)
This causes a window where setting of PG_A or PG_M of the pte
caused by page access of a second CPU can be ignored or overwritten
and lost.
Lost PG_M bits can cause data loss.
(Page not written to backing storage)
>How-To-Repeat:
>Fix:
Import the pte update logic from the newest NetBSD pmap.
The NetBSD pmap also tries to avoid unnecessary TLB shootdowns.
>Release-Note:
>Audit-Trail:
>Unformatted:
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