Module Name: src
Committed By: riastradh
Date: Sun Oct 30 10:26:48 UTC 2022
Modified Files:
src/sys/arch/aarch64/aarch64: pmap.c
Log Message:
aarch64/pmap(9): Teach pmap_protect about pmap_kenter_pa mappings.
Pages mapped with pmap_kenter_pa are necessarily unmanaged, so there
are no P->V records, and pmap_kenter_pa leaves pp->pp_pv.pv_va zero
with no modified/referenced state.
However, pmap_protect erroneously examined pp->pp_pv.pv_va to
ascertain the modified/referenced state -- and if the page was not
marked referenced, pmap_protect would clear the LX_BLKPAG_AF bit
(Access Flag), with the effect that subsequent uses of the page fault
and require a detour through pmap_fault_fixup.
This caused problems for the kernel module loader:
- When loading the text section, kobj_load first allocates kva with
uvm_km_alloc(UVM_KMF_WIRED|UVM_KMF_EXEC), which creates ptes with
pmap_kenter_pa. These ptes are writable, so we can copy the text
section into them, and have LX_BLKPAG_AF set so there will be no
fault when they are used by the kernel.
- But then kobj_affix makes the text section read/execute-only (and
nonwritable) with uvm_km_protect(VM_PROT_READ|VM_PROT_EXECUTE),
which updates the ptes with pmap_protect. This _should_ leave
LX_BLKPAG_AF set, but by inadvertently treating the page as managed
when it should be unmanaged, pmap_protect cleared it instead.
- Most of the time, clearing LX_BLKPAG_AF caused no problem, because
pmap_fault_fixup would silently resolve it. But if a hard
interrupt handler tried to use any page in the module's text (or
rodata, I suspect) that was not yet fixed up, the CPU would fault
and enter pmap_fault_fixup -- which would promptly crash (or hang)
by trying to take the pmap lock in interrupt context, which is
forbidden.
I observed this by loading dtrace.kmod early at boot and trying to
dtrace hard interrupt handlers.
With this change, pmap_protect now recognizes wired mappings (as
created by pmap_kenter_pa) before consulting pp->pp_pv.pv_va, and
preserves then LX_BLKPAG_AF bit in that case.
ok skrll
To generate a diff of this commit:
cvs rdiff -u -r1.145 -r1.146 src/sys/arch/aarch64/aarch64/pmap.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/aarch64/aarch64/pmap.c
diff -u src/sys/arch/aarch64/aarch64/pmap.c:1.145 src/sys/arch/aarch64/aarch64/pmap.c:1.146
--- src/sys/arch/aarch64/aarch64/pmap.c:1.145 Sat Oct 29 07:21:41 2022
+++ src/sys/arch/aarch64/aarch64/pmap.c Sun Oct 30 10:26:48 2022
@@ -1,4 +1,4 @@
-/* $NetBSD: pmap.c,v 1.145 2022/10/29 07:21:41 skrll Exp $ */
+/* $NetBSD: pmap.c,v 1.146 2022/10/30 10:26:48 riastradh Exp $ */
/*
* Copyright (c) 2017 Ryo Shimizu <r...@nerv.org>
@@ -27,7 +27,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.145 2022/10/29 07:21:41 skrll Exp $");
+__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.146 2022/10/30 10:26:48 riastradh Exp $");
#include "opt_arm_debug.h"
#include "opt_cpuoptions.h"
@@ -1410,9 +1410,7 @@ pmap_protect(struct pmap *pm, vaddr_t sv
#ifdef UVMHIST
pt_entry_t opte;
#endif
- struct vm_page *pg;
struct pmap_page *pp;
- paddr_t pa;
uint32_t mdattr;
bool executable;
@@ -1428,24 +1426,30 @@ pmap_protect(struct pmap *pm, vaddr_t sv
continue;
}
- pa = lxpde_pa(pte);
- pg = PHYS_TO_VM_PAGE(pa);
- if (pg != NULL) {
- pp = VM_PAGE_TO_PP(pg);
- PMAP_COUNT(protect_managed);
- } else {
+ if (pte & LX_BLKPAG_NG) {
+ const paddr_t pa = lxpde_pa(pte);
+ struct vm_page *const pg = PHYS_TO_VM_PAGE(pa);
+
+ if (pg != NULL) {
+ pp = VM_PAGE_TO_PP(pg);
+ PMAP_COUNT(protect_managed);
+ } else {
#ifdef __HAVE_PMAP_PV_TRACK
- pp = pmap_pv_tracked(pa);
+ pp = pmap_pv_tracked(pa);
#ifdef PMAPCOUNTERS
- if (pp != NULL)
- PMAP_COUNT(protect_pvmanaged);
- else
- PMAP_COUNT(protect_unmanaged);
+ if (pp != NULL)
+ PMAP_COUNT(protect_pvmanaged);
+ else
+ PMAP_COUNT(protect_unmanaged);
#endif
#else
+ pp = NULL;
+ PMAP_COUNT(protect_unmanaged);
+#endif /* __HAVE_PMAP_PV_TRACK */
+ }
+ } else { /* kenter */
pp = NULL;
PMAP_COUNT(protect_unmanaged);
-#endif /* __HAVE_PMAP_PV_TRACK */
}
if (pp != NULL) {
