From c36743d23f1edd16b34eabb0153f27f5f763ce0f Mon Sep 17 00:00:00 2001 From: kib Date: Sun, 27 Apr 2014 05:19:01 +0000 Subject: [PATCH] When vm_fault_copy_entry() is called from vm_map_protect() for a wired entry and performs the upgrade of the entry permissions from read-only to read-write, we must allow to search for the source pages in the backing object, like we do in the case of forking the read-only wired entry. For the fork case, the behaviour is allowed by src_readonly boolean, which in fact is only used to assert that read-write case provides all source pages in the top-level object. Eliminate the src_readonly variable. Allow for the copy loop to look into the backing objects, add explicit asserts to ensure that only read-only and upgrade case actually does. Expand comments. Change the panic call into assert. Reported by: markj Tested by: markj, pho (previous version) Reviewed by: alc Sponsored by: The FreeBSD Foundation MFC after: 1 week --- sys/vm/vm_fault.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c index ba7692c2af5..3faf28b0407 100644 --- a/sys/vm/vm_fault.c +++ b/sys/vm/vm_fault.c @@ -1240,7 +1240,7 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map, vm_offset_t vaddr; vm_page_t dst_m; vm_page_t src_m; - boolean_t src_readonly, upgrade; + boolean_t upgrade; #ifdef lint src_map++; @@ -1250,7 +1250,6 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map, src_object = src_entry->object.vm_object; src_pindex = OFF_TO_IDX(src_entry->offset); - src_readonly = (src_entry->protection & VM_PROT_WRITE) == 0; /* * Create the top-level object for the destination entry. (Doesn't @@ -1321,25 +1320,33 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map, /* * Find the page in the source object, and copy it in. - * (Because the source is wired down, the page will be in - * memory.) + * Because the source is wired down, the page will be + * in memory. */ VM_OBJECT_RLOCK(src_object); object = src_object; pindex = src_pindex + dst_pindex; while ((src_m = vm_page_lookup(object, pindex)) == NULL && - src_readonly && (backing_object = object->backing_object) != NULL) { /* - * Allow fallback to backing objects if we are reading. + * Unless the source mapping is read-only or + * it is presently being upgraded from + * read-only, the first object in the shadow + * chain should provide all of the pages. In + * other words, this loop body should never be + * executed when the source mapping is already + * read/write. */ + KASSERT((src_entry->protection & VM_PROT_WRITE) == 0 || + upgrade, + ("vm_fault_copy_entry: main object missing page")); + VM_OBJECT_RLOCK(backing_object); pindex += OFF_TO_IDX(object->backing_object_offset); VM_OBJECT_RUNLOCK(object); object = backing_object; } - if (src_m == NULL) - panic("vm_fault_copy_wired: page missing"); + KASSERT(src_m != NULL, ("vm_fault_copy_entry: page missing")); pmap_copy_page(src_m, dst_m); VM_OBJECT_RUNLOCK(object); dst_m->valid = VM_PAGE_BITS_ALL; -- 2.45.0