git: a48f51b3d396 - main - arm64: Use the right PTE when downgrading perms in pmap_promote_l2()

[Mark Johnston]

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=a48f51b3d396664f9b0a91f016159f4e4324da85

commit a48f51b3d396664f9b0a91f016159f4e4324da85
Author:     Mark Johnston <markj at FreeBSD.org>
AuthorDate: 2021-06-06 20:40:29 +0000
Commit:     Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-06-06 20:44:46 +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
    MFC after:      1 week
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D30642
---
 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 bc5d228af5ad..c26c3d8fce17 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;