git: 325ff9327459 - main - Clear the accessed bit when copying a managed superpage mapping

[Alan Cox]

The branch main has been updated by alc:

URL: https://cgit.FreeBSD.org/src/commit/?id=325ff9327459bc7307130675fa19367ff8b02310

commit 325ff9327459bc7307130675fa19367ff8b02310
Author:     Alan Cox <alc at FreeBSD.org>
AuthorDate: 2021-07-13 07:30:43 +0000
Commit:     Alan Cox <alc at FreeBSD.org>
CommitDate: 2021-07-14 18:06:10 +0000

    Clear the accessed bit when copying a managed superpage mapping
    
    pmap_copy() is used to speculatively create mappings, so those mappings
    should not have their access bit preset.
    
    Reviewed by:    kib, markj
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D31162
---
 sys/amd64/amd64/pmap.c | 17 ++++++++++++++++-
 sys/arm64/arm64/pmap.c | 18 ++++++++++++++++--
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index 31681e255af1..427fbdf44830 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -7775,6 +7775,9 @@ pmap_copy(pmap_t dst_pmap, pmap_t src_pmap, vm_offset_t dst_addr, vm_size_t len,
 			continue;
 			
 		if (srcptepaddr & PG_PS) {
+			/*
+			 * We can only virtual copy whole superpages.
+			 */
 			if ((addr & PDRMASK) != 0 || addr + NBPDR > end_addr)
 				continue;
 			pde = pmap_alloc_pde(dst_pmap, addr, &dst_pdpg, NULL);
@@ -7783,7 +7786,19 @@ pmap_copy(pmap_t dst_pmap, pmap_t src_pmap, vm_offset_t dst_addr, vm_size_t len,
 			if (*pde == 0 && ((srcptepaddr & PG_MANAGED) == 0 ||
 			    pmap_pv_insert_pde(dst_pmap, addr, srcptepaddr,
 			    PMAP_ENTER_NORECLAIM, &lock))) {
-				*pde = srcptepaddr & ~PG_W;
+				/*
+				 * We leave the dirty bit unchanged because
+				 * managed read/write superpage mappings are
+				 * required to be dirty.  However, managed
+				 * superpage mappings are not required to
+				 * have their accessed bit set, so we clear
+				 * it because we don't know if this mapping
+				 * will be used.
+				 */
+				srcptepaddr &= ~PG_W;
+				if ((srcptepaddr & PG_MANAGED) != 0)
+					srcptepaddr &= ~PG_A;
+				*pde = srcptepaddr;
 				pmap_resident_count_adj(dst_pmap, NBPDR /
 				    PAGE_SIZE);
 				counter_u64_add(pmap_pde_mappings, 1);
diff --git a/sys/arm64/arm64/pmap.c b/sys/arm64/arm64/pmap.c
index 8ed1b86bd58c..678feae55c25 100644
--- a/sys/arm64/arm64/pmap.c
+++ b/sys/arm64/arm64/pmap.c
@@ -4557,6 +4557,9 @@ pmap_copy(pmap_t dst_pmap, pmap_t src_pmap, vm_offset_t dst_addr, vm_size_t len,
 		if (srcptepaddr == 0)
 			continue;
 		if ((srcptepaddr & ATTR_DESCR_MASK) == L2_BLOCK) {
+			/*
+			 * We can only virtual copy whole superpages.
+			 */
 			if ((addr & L2_OFFSET) != 0 ||
 			    addr + L2_SIZE > end_addr)
 				continue;
@@ -4567,8 +4570,19 @@ 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_SW_WIRED;
-				pmap_store(l2, srcptepaddr & ~mask);
+				/*
+				 * We leave the dirty bit unchanged because
+				 * managed read/write superpage mappings are
+				 * required to be dirty.  However, managed
+				 * superpage mappings are not required to
+				 * have their accessed bit set, so we clear
+				 * it because we don't know if this mapping
+				 * will be used.
+				 */
+				srcptepaddr &= ~ATTR_SW_WIRED;
+				if ((srcptepaddr & ATTR_SW_MANAGED) != 0)
+					srcptepaddr &= ~ATTR_AF;
+				pmap_store(l2, srcptepaddr);
 				pmap_resident_count_inc(dst_pmap, L2_SIZE /
 				    PAGE_SIZE);
 				atomic_add_long(&pmap_l2_mappings, 1);