Fix a typo in the original import of this code from NetBSD that caused the

wrong element of the VSID bitmap array to be examined after a collision,
leading to reallocation of in-use VSIDs under some circumstances, with
attendant memory corruption. Also add an assert to check for this kind of
problem in the future.

MFC after:	4 days

2 files changed, 4 insertions, 2 deletions

diff --git a/sys/powerpc/aim/mmu_oea.c b/sys/powerpc/aim/mmu_oea.c
index d3a2459..2ade00f 100644
--- a/sys/powerpc/aim/mmu_oea.c
+++ b/sys/powerpc/aim/mmu_oea.c
@@ -1618,7 +1618,7 @@ moea_pinit(mmu_t mmu, pmap_t pmap)
 				entropy = (moea_vsidcontext >> 20);
 				continue;
 			}
-			i = ffs(~moea_vsid_bitmap[i]) - 1;
+			i = ffs(~moea_vsid_bitmap[n]) - 1;
 			mask = 1 << i;
 			hash &= 0xfffff & ~(VSID_NBPW - 1);
 			hash |= i;
diff --git a/sys/powerpc/aim/mmu_oea64.c b/sys/powerpc/aim/mmu_oea64.c
index c1b6f2c..8cf8349 100644
--- a/sys/powerpc/aim/mmu_oea64.c
+++ b/sys/powerpc/aim/mmu_oea64.c
@@ -2080,11 +2080,13 @@ moea64_get_unique_vsid(void) {
 				entropy = (moea64_vsidcontext >> 20);
 				continue;
 			}
-			i = ffs(~moea64_vsid_bitmap[i]) - 1;
+			i = ffs(~moea64_vsid_bitmap[n]) - 1;
 			mask = 1 << i;
 			hash &= VSID_HASHMASK & ~(VSID_NBPW - 1);
 			hash |= i;
 		}
+		KASSERT(!(moea64_vsid_bitmap[n] & mask),
+		    ("Allocating in-use VSID %#x\n", hash));
 		moea64_vsid_bitmap[n] |= mask;
 		mtx_unlock(&moea64_slb_mutex);
 		return (hash);