Messages in this thread | | | Subject | Re: [PATCH v2 09/17] powerpc/mm: Add new hash_page_mm() | From | Michael Neuling <> | Date | Thu, 02 Oct 2014 17:39:23 +1000 |
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On Thu, 2014-10-02 at 13:48 +1000, Michael Ellerman wrote: > On Tue, 2014-30-09 at 10:34:58 UTC, Michael Neuling wrote: > > From: Ian Munsie <imunsie@au1.ibm.com> > > > > This adds a new function hash_page_mm() based on the existing hash_page(). > > This version allows any struct mm to be passed in, rather than assuming > > current. This is useful for servicing co-processor faults which are not in the > > context of the current running process. > > I'm not a big fan. hash_page() is already a train wreck, and this doesn't make > it any better.
I can document it to make the situation a bit better. It's certainly not clear which one to use here and under what circumstances. It's basically ask benh territory.
> > diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c > > index bbdb054..0a5c8c0 100644 > > --- a/arch/powerpc/mm/hash_utils_64.c > > +++ b/arch/powerpc/mm/hash_utils_64.c > > @@ -904,7 +904,7 @@ void demote_segment_4k(struct mm_struct *mm, unsigned long addr) > > return; > > slice_set_range_psize(mm, addr, 1, MMU_PAGE_4K); > > copro_flush_all_slbs(mm); > > - if (get_paca_psize(addr) != MMU_PAGE_4K) { > > + if ((get_paca_psize(addr) != MMU_PAGE_4K) && (current->mm == mm)) { > > get_paca()->context = mm->context; > > slb_flush_and_rebolt(); > > This is a bit fishy. > > If that mm is currently running on another cpu you just failed to update it's > paca. But I think the call to check_paca_psize() in hash_page() will save you > on that cpu. > > In fact we might be able to remove that synchronisation from > demote_segment_4k() and always leave it up to check_paca_psize()?
Aneesh asked the same thing for v1 and we convinced ourselves it was ok. I said this at the time...
I had a chat to benh offline about this and he thinks it's fine. A running process in the same mm context will either have hit this mapping or not. If it's hit it, the page will be invalidated and it'll come in via hash_page and have it's segment demoted also (and paca updated). If it hasn't hit, again it'll come into hash_page() and get demoted also.
> > @@ -989,26 +989,24 @@ static void check_paca_psize(unsigned long ea, struct mm_struct *mm, > > * -1 - critical hash insertion error > > * -2 - access not permitted by subpage protection mechanism > > */ > > -int hash_page(unsigned long ea, unsigned long access, unsigned long trap) > > +int hash_page_mm(struct mm_struct *mm, unsigned long ea, unsigned long access, unsigned long trap) > > { > > enum ctx_state prev_state = exception_enter(); > > pgd_t *pgdir; > > unsigned long vsid; > > - struct mm_struct *mm; > > pte_t *ptep; > > unsigned hugeshift; > > const struct cpumask *tmp; > > int rc, user_region = 0, local = 0; > > int psize, ssize; > > > > - DBG_LOW("hash_page(ea=%016lx, access=%lx, trap=%lx\n", > > - ea, access, trap); > > + DBG_LOW("%s(ea=%016lx, access=%lx, trap=%lx\n", > > + __func__, ea, access, trap); > > > > /* Get region & vsid */ > > switch (REGION_ID(ea)) { > > case USER_REGION_ID: > > user_region = 1; > > - mm = current->mm; > > if (! mm) { > > DBG_LOW(" user region with no mm !\n"); > > rc = 1; > > What about the VMALLOC case where we do: > mm = &init_mm; > > Is that what you want? It seems odd that you pass an mm to the routine, but > then potentially it ends up using a different mm after all depending on the > address.
Good point. We have hash_page() still. I can make that check in there and decide which mm to use and pass that to hash_page_mm(). Then we always use mm in hash_page_mm(). hash_page() will then look like this:
int hash_page(unsigned long ea, unsigned long access, unsigned long trap) { struct mm_struct *mm = current->mm;
if (REGION_ID(ea) == VMALLOC_REGION_ID) mm = &init_mm;
return hash_page_mm(mm, ea, access, trap); }
Mikey
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