Date: Thu, 4 Jul 2013 10:38:14 +0000 (UTC) From: Grzegorz Bernacki <gber@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r252694 - head/sys/arm/arm Message-ID: <201307041038.r64AcEUa059226@svn.freebsd.org>
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Author: gber Date: Thu Jul 4 10:38:14 2013 New Revision: 252694 URL: http://svnweb.freebsd.org/changeset/base/252694 Log: Fix modified bit emulation for ARMv6/v7 When doing pmap_enter_locked(), enable write permission only when access type indicates attempt to write. Otherwise, leave the page read only but mark it writable in pv_flags. This will result in: 1. Marking page writable during pmap_enter() but only when ensured that it will be written right away so that we will not get redundant permissions fault on write attempt. 2. Keeping page read only when it is permitted to be written but there was no actual write attempt. Hence, we will get permissions fault on write access and mark page writable in pmap_fault_fixup() what will indicate modification status. Submitted by: Zbigniew Bodek <zbb@semihalf.com> Sponsored by: The FreeBSD Foundation, Semihalf Modified: head/sys/arm/arm/pmap-v6.c Modified: head/sys/arm/arm/pmap-v6.c ============================================================================== --- head/sys/arm/arm/pmap-v6.c Thu Jul 4 08:59:34 2013 (r252693) +++ head/sys/arm/arm/pmap-v6.c Thu Jul 4 10:38:14 2013 (r252694) @@ -2801,8 +2801,13 @@ validate: } if (prot & VM_PROT_WRITE) { - /* Write enable */ - npte &= ~(L2_APX); + /* + * Enable write permission if the access type + * indicates write intention. Emulate modified + * bit otherwise. + */ + if ((access & VM_PROT_WRITE) != 0) + npte &= ~(L2_APX); if ((m->oflags & VPO_UNMANAGED) == 0) { vm_page_aflag_set(m, PGA_WRITEABLE);
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