git: 4e4035ef1fb5 - main - arm64: Fix pmap_copy()'s handling of 2MB mappings

[Mark Johnston]

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=4e4035ef1fb5e2f9da6b658ffae8a54862b4d018

commit 4e4035ef1fb5e2f9da6b658ffae8a54862b4d018
Author:     Mark Johnston <markj at FreeBSD.org>
AuthorDate: 2021-06-06 20:40:45 +0000
Commit:     Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-06-06 20:44:46 +0000

    arm64: Fix pmap_copy()'s handling of 2MB mappings
    
    When copying mappings from parent to child, we clear the accessed and
    dirty bits.  This is done for both 4KB and 2MB PTEs.  However,
    pmap_demote_l2() asserts that writable superpages must be dirty.  This
    is to avoid races with the MMU setting the dirty bit during promotion
    and demotion.  pmap_copy() can create clean, writable superpage
    mappings, so it violates this assertion.
    
    Modify pmap_copy() to preserve the accessed and dirty bits when copying
    2MB mappings, like we do on amd64.
    
    Fixes:          ca2cae0b4dd
    Reported by:    Jenkins via mhorne
    Reviewed by:    alc, kib
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D30643
---
 sys/arm64/arm64/pmap.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/sys/arm64/arm64/pmap.c b/sys/arm64/arm64/pmap.c
index c26c3d8fce17..ffc83be852bd 100644
--- a/sys/arm64/arm64/pmap.c
+++ b/sys/arm64/arm64/pmap.c
@@ -4573,11 +4573,8 @@ pmap_copy(pmap_t dst_pmap, pmap_t src_pmap, vm_offset_t dst_addr, vm_size_t len,
 			    ((srcptepaddr & ATTR_SW_MANAGED) == 0 ||
 			    pmap_pv_insert_l2(dst_pmap, addr, srcptepaddr,
 			    PMAP_ENTER_NORECLAIM, &lock))) {
-				mask = ATTR_AF | ATTR_SW_WIRED;
-				nbits = 0;
-				if ((srcptepaddr & ATTR_SW_DBM) != 0)
-					nbits |= ATTR_S1_AP_RW_BIT;
-				pmap_store(l2, (srcptepaddr & ~mask) | nbits);
+				mask = ATTR_SW_WIRED;
+				pmap_store(l2, srcptepaddr & ~mask);
 				pmap_resident_count_inc(dst_pmap, L2_SIZE /
 				    PAGE_SIZE);
 				atomic_add_long(&pmap_l2_mappings, 1);