From ad55cd76a626ea688c4fc512b9a3d7c6d05bc32e Mon Sep 17 00:00:00 2001 From: Grzegorz Bernacki Date: Thu, 4 Jul 2013 10:38:14 +0000 Subject: [PATCH] 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 Sponsored by: The FreeBSD Foundation, Semihalf --- sys/arm/arm/pmap-v6.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/sys/arm/arm/pmap-v6.c b/sys/arm/arm/pmap-v6.c index 9e0b8bda319b..4ad00673db6f 100644 --- a/sys/arm/arm/pmap-v6.c +++ b/sys/arm/arm/pmap-v6.c @@ -2801,8 +2801,13 @@ pmap_enter_locked(pmap_t pmap, vm_offset_t va, vm_prot_t access, vm_page_t m, } 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);