> Date: Wed, 8 Sep 2021 10:45:53 +0200
> From: Martin Pieuchot <[email protected]>
>
> On 07/09/21(Tue) 14:19, Patrick Wildt wrote:
> > Hi,
> >
> > I was playing around a little with the mutex code and found that on
> > arm64 there some uninitialized mutexes out there.
> >
> > I think the arm64 specific one is comparatively easy to solve. We
> > either initialize the mtx when we initialize the rest of the pmap, or
> > we move it into the global definition of those. I opted for the former
> > version.
>
> Is the kernel pmap mutex supposed to be used? On i386 it isn't so the
> mutex's IPL is set to -1 and we added a KASSERT() in splraise() to spot
> any mistake.
Indeed. The kernel pmap is special:
* It can never disappear.
* Page table pages are pre-allocated and are never freed.
* Mappings are (largely) unmanaged (by uvm).
Therefore the per-pmap lock isn't used for the kernel map on most
(all?) architectures.
> > The other one prolly needs more discussion/debugging. So uvm_init()
> > calls first pmap_init() and then uvm_km_page_init(). The latter does
> > initialize the mutex, but arm64's pmap_init() already uses pools, which
> > uses km_alloc, which then uses that mutex. Now one easy fix would be
> > to just initialize the definition right away instead of during runtime.
> >
> > But there might be the question if arm64's pmap is allowed to use pools
> > and km_alloc during pmap_init.
>
> That's a common question for the family of pmaps calling pool_setlowat()
> in pmap_init(). That's where pool_prime() is called from.
>
> > #0 0xffffff800073f984 in mtx_enter (mtx=0xffffff8000f3b048 <uvm_km_pages>)
> > at /usr/src/sys/kern/kern_lock.c:281
> > #1 0xffffff8000937e6c in km_alloc (sz=<error reading variable: Unhandled
> > dwarf expression opcode 0xa3>, kv=0xffffff8000da6a30 <kv_page>,
> > kp=0xffffff8000da6a48 <kp_dirty>, kd=0xffffff8000e934d8)
> > at /usr/src/sys/uvm/uvm_km.c:899
> > #2 0xffffff800084d804 in pool_page_alloc (pp=<error reading variable:
> > Unhandled dwarf expression opcode 0xa3>, flags=<error reading variable:
> > Unhandled dwarf expression opcode 0xa3>,
> > slowdown=<error reading variable: Unhandled dwarf expression opcode
> > 0xa3>) at /usr/src/sys/kern/subr_pool.c:1633
> > #3 0xffffff800084f8dc in pool_allocator_alloc (pp=0xffffff8000ea6e40
> > <pmap_pmap_pool>, flags=65792, slowdown=0xffffff80026cd098) at
> > /usr/src/sys/kern/subr_pool.c:1602
> > #4 0xffffff800084ef08 in pool_p_alloc (pp=0xffffff8000ea6e40
> > <pmap_pmap_pool>, flags=2, slowdown=0xffffff8000e9359c) at
> > /usr/src/sys/kern/subr_pool.c:926
> > #5 0xffffff800084f808 in pool_prime (pp=<optimized out>, n=<error reading
> > variable: Unhandled dwarf expression opcode 0xa3>) at
> > /usr/src/sys/kern/subr_pool.c:896
> > #6 0xffffff800048c20c in pmap_init () at
> > /usr/src/sys/arch/arm64/arm64/pmap.c:1682
> > #7 0xffffff80009384dc in uvm_init () at /usr/src/sys/uvm/uvm_init.c:118
> > #8 0xffffff800048e664 in main (framep=<error reading variable: Unhandled
> > dwarf expression opcode 0xa3>) at /usr/src/sys/kern/init_main.c:235
> >
> > diff --git a/sys/arch/arm64/arm64/pmap.c b/sys/arch/arm64/arm64/pmap.c
> > index 79a344cc84e..f070f4540ec 100644
> > --- a/sys/arch/arm64/arm64/pmap.c
> > +++ b/sys/arch/arm64/arm64/pmap.c
> > @@ -1308,10 +1308,12 @@ pmap_bootstrap(long kvo, paddr_t lpt1, long
> > kernelstart, long kernelend,
> > pmap_kernel()->pm_vp.l1 = (struct pmapvp1 *)va;
> > pmap_kernel()->pm_privileged = 1;
> > pmap_kernel()->pm_asid = 0;
> > + mtx_init(&pmap_kernel()->pm_mtx, IPL_VM);
> >
> > pmap_tramp.pm_vp.l1 = (struct pmapvp1 *)va + 1;
> > pmap_tramp.pm_privileged = 1;
> > pmap_tramp.pm_asid = 0;
> > + mtx_init(&pmap_tramp.pm_mtx, IPL_VM);
> >
> > /* Mark ASID 0 as in-use. */
> > pmap_asid[0] |= (3U << 0);
> > diff --git a/sys/uvm/uvm_km.c b/sys/uvm/uvm_km.c
> > index 4a60377e9d7..e77afeda832 100644
> > --- a/sys/uvm/uvm_km.c
> > +++ b/sys/uvm/uvm_km.c
> > @@ -644,7 +644,7 @@ uvm_km_page_lateinit(void)
> > * not zero filled.
> > */
> >
> > -struct uvm_km_pages uvm_km_pages;
> > +struct uvm_km_pages uvm_km_pages = { .mtx = MUTEX_INITIALIZER(IPL_VM) };
> >
> > void uvm_km_createthread(void *);
> > void uvm_km_thread(void *);
> > @@ -664,7 +664,6 @@ uvm_km_page_init(void)
> > int len, bulk;
> > vaddr_t addr;
> >
> > - mtx_init(&uvm_km_pages.mtx, IPL_VM);
> > if (!uvm_km_pages.lowat) {
> > /* based on physmem, calculate a good value here */
> > uvm_km_pages.lowat = physmem / 256;
> >
>
>
