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.
