git: e58cb5c01de9 - stable/13 - arm64: Use the right PTE when downgrading perms in pmap_promote_l2()

[Mark Johnston]

The branch stable/13 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=e58cb5c01de989c8f88af3732a5fe404b0660a9c

commit e58cb5c01de989c8f88af3732a5fe404b0660a9c
Author:     Mark Johnston <markj at FreeBSD.org>
AuthorDate: 2021-06-06 20:40:29 +0000
Commit:     Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-06-14 20:25:14 +0000

    arm64: Use the right PTE when downgrading perms in pmap_promote_l2()
    
    When promoting a run of small mappings to a superpage, we have to
    downgrade clean, writable mappings to read-only, to handle the
    possibility that the MMU will concurrently mark one of the mappings as
    dirty.
    
    The code which performed this operation for the first PTE in the run
    used the wrong PTE pointer.  As a result, the comparison would always
    fail, aborting the promotion.  This only occurs when promoting writable,
    clean mappings.
    
    Fixes:          ca2cae0b4dd
    Reviewed by:    alc, kib
    Sponsored by:   The FreeBSD Foundation
    
    (cherry picked from commit a48f51b3d396664f9b0a91f016159f4e4324da85)
---
 sys/arm64/arm64/pmap.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/sys/arm64/arm64/pmap.c b/sys/arm64/arm64/pmap.c
index efe6bdd3d034..b49ec4194e19 100644
--- a/sys/arm64/arm64/pmap.c
+++ b/sys/arm64/arm64/pmap.c
@@ -3518,7 +3518,11 @@ setl2:
 
 	if ((newl2 & (ATTR_S1_AP_RW_BIT | ATTR_SW_DBM)) ==
 	    (ATTR_S1_AP(ATTR_S1_AP_RO) | ATTR_SW_DBM)) {
-		if (!atomic_fcmpset_64(l2, &newl2, newl2 & ~ATTR_SW_DBM))
+		/*
+		 * When the mapping is clean, i.e., ATTR_S1_AP_RO is set,
+		 * ATTR_SW_DBM can be cleared without a TLB invalidation.
+		 */
+		if (!atomic_fcmpset_64(firstl3, &newl2, newl2 & ~ATTR_SW_DBM))
 			goto setl2;
 		newl2 &= ~ATTR_SW_DBM;
 	}
@@ -3529,6 +3533,11 @@ setl2:
 setl3:
 		if ((oldl3 & (ATTR_S1_AP_RW_BIT | ATTR_SW_DBM)) ==
 		    (ATTR_S1_AP(ATTR_S1_AP_RO) | ATTR_SW_DBM)) {
+			/*
+			 * When the mapping is clean, i.e., ATTR_S1_AP_RO is
+			 * set, ATTR_SW_DBM can be cleared without a TLB
+			 * invalidation.
+			 */
 			if (!atomic_fcmpset_64(l3, &oldl3, oldl3 &
 			    ~ATTR_SW_DBM))
 				goto setl3;