Messages in this thread | | | Subject | Re: [PATCH 3/5] mm/hmm: Use mm_get_hmm() in hmm_range_register() | From | Ralph Campbell <> | Date | Thu, 23 May 2019 11:19:53 -0700 |
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On 5/23/19 5:51 AM, Jason Gunthorpe wrote: > On Mon, May 06, 2019 at 04:29:40PM -0700, rcampbell@nvidia.com wrote: >> From: Ralph Campbell <rcampbell@nvidia.com> >> >> In hmm_range_register(), the call to hmm_get_or_create() implies that >> hmm_range_register() could be called before hmm_mirror_register() when >> in fact, that would violate the HMM API. >> >> Use mm_get_hmm() instead of hmm_get_or_create() to get the HMM structure. >> >> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> >> Cc: John Hubbard <jhubbard@nvidia.com> >> Cc: Ira Weiny <ira.weiny@intel.com> >> Cc: Dan Williams <dan.j.williams@intel.com> >> Cc: Arnd Bergmann <arnd@arndb.de> >> Cc: Balbir Singh <bsingharora@gmail.com> >> Cc: Dan Carpenter <dan.carpenter@oracle.com> >> Cc: Matthew Wilcox <willy@infradead.org> >> Cc: Souptick Joarder <jrdr.linux@gmail.com> >> Cc: Andrew Morton <akpm@linux-foundation.org> >> mm/hmm.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/hmm.c b/mm/hmm.c >> index f6c4c8633db9..2aa75dbed04a 100644 >> +++ b/mm/hmm.c >> @@ -936,7 +936,7 @@ int hmm_range_register(struct hmm_range *range, >> range->start = start; >> range->end = end; >> >> - range->hmm = hmm_get_or_create(mm); >> + range->hmm = mm_get_hmm(mm); >> if (!range->hmm) >> return -EFAULT; > > I looked for documentation saying that hmm_range_register should only > be done inside a hmm_mirror_register and didn't see it. Did I miss it?
Yes, hmm_mirror_register() has to be called before hmm_range_register(). Look at Documentation/vm/hmm.rst for "Address space mirroring implementation and API".
> Can you add a comment?
Sure, although I think your idea to pass hmm_mirror to hmm_range_register() makes sense and makes it clear.
> It is really good to fix this because it means we can rely on mmap sem > to manage mm->hmm! > > If this is true then I also think we should change the signature of > the function to make this dependency relationship clear, and remove > some possible confusing edge cases. > > What do you think about something like this? (unfinished) > > commit 29098bd59cf481ad1915db40aefc8435dabb8b28 > Author: Jason Gunthorpe <jgg@mellanox.com> > Date: Thu May 23 09:41:19 2019 -0300 > > mm/hmm: Use hmm_mirror not mm as an argument for hmm_register_range > > Ralf observes that hmm_register_range() can only be called by a driver > while a mirror is registered. Make this clear in the API by passing > in the mirror structure as a parameter. > > This also simplifies understanding the lifetime model for struct hmm, > as the hmm pointer must be valid as part of a registered mirror > so all we need in hmm_register_range() is a simple kref_get. > > Suggested-by: Ralph Campbell <rcampbell@nvidia.com> > Signed-off-by: Jason Gunthorpe <jgg@mellanox.com> > > diff --git a/include/linux/hmm.h b/include/linux/hmm.h > index 8b91c90d3b88cb..87d29e085a69f7 100644 > --- a/include/linux/hmm.h > +++ b/include/linux/hmm.h > @@ -503,7 +503,7 @@ static inline bool hmm_mirror_mm_is_alive(struct hmm_mirror *mirror) > * Please see Documentation/vm/hmm.rst for how to use the range API. > */ > int hmm_range_register(struct hmm_range *range, > - struct mm_struct *mm, > + struct hmm_mirror *mirror, > unsigned long start, > unsigned long end, > unsigned page_shift); > @@ -539,7 +539,8 @@ static inline bool hmm_vma_range_done(struct hmm_range *range) > } > > /* This is a temporary helper to avoid merge conflict between trees. */ > -static inline int hmm_vma_fault(struct hmm_range *range, bool block) > +static inline int hmm_vma_fault(struct hmm_mirror *mirror, > + struct hmm_range *range, bool block) > { > long ret; > > @@ -552,7 +553,7 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block) > range->default_flags = 0; > range->pfn_flags_mask = -1UL; > > - ret = hmm_range_register(range, range->vma->vm_mm, > + ret = hmm_range_register(range, mirror, > range->start, range->end, > PAGE_SHIFT); > if (ret) > diff --git a/mm/hmm.c b/mm/hmm.c > index 824e7e160d8167..fa1b04fcfc2549 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -927,7 +927,7 @@ static void hmm_pfns_clear(struct hmm_range *range, > * Track updates to the CPU page table see include/linux/hmm.h > */ > int hmm_range_register(struct hmm_range *range, > - struct mm_struct *mm, > + struct hmm_mirror *mirror, > unsigned long start, > unsigned long end, > unsigned page_shift) > @@ -935,7 +935,6 @@ int hmm_range_register(struct hmm_range *range, > unsigned long mask = ((1UL << page_shift) - 1UL); > > range->valid = false; > - range->hmm = NULL; > > if ((start & mask) || (end & mask)) > return -EINVAL; > @@ -946,15 +945,12 @@ int hmm_range_register(struct hmm_range *range, > range->start = start; > range->end = end; > > - range->hmm = hmm_get_or_create(mm); > - if (!range->hmm) > - return -EFAULT; > - > /* Check if hmm_mm_destroy() was call. */ > - if (range->hmm->mm == NULL || range->hmm->dead) { > - hmm_put(range->hmm); > + if (mirror->hmm->mm == NULL || mirror->hmm->dead) > return -EFAULT; > - } > + > + range->hmm = mirror->hmm; > + kref_get(&range->hmm->kref); > > /* Initialize range to track CPU page table update */ > mutex_lock(&range->hmm->lock); >
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