Re: [PATCHv2 1/9] mm: Introduce new vm_insert_range and vm_insert_range_buggy API

[Mike Rapoport]

On Thu, Jan 31, 2019 at 03:43:39PM +0530, Souptick Joarder wrote:
> On Thu, Jan 31, 2019 at 2:09 PM Mike Rapoport <rppt@xxxxxxxxxxxxx> wrote:
> >
> > On Thu, Jan 31, 2019 at 08:38:12AM +0530, Souptick Joarder wrote:
> > > Previouly drivers have their own way of mapping range of
> > > kernel pages/memory into user vma and this was done by
> > > invoking vm_insert_page() within a loop.
> > >
> > > As this pattern is common across different drivers, it can
> > > be generalized by creating new functions and use it across
> > > the drivers.
> > >
> > > vm_insert_range() is the API which could be used to mapped
> > > kernel memory/pages in drivers which has considered vm_pgoff
> > >
> > > vm_insert_range_buggy() is the API which could be used to map
> > > range of kernel memory/pages in drivers which has not considered
> > > vm_pgoff. vm_pgoff is passed default as 0 for those drivers.
> > >
> > > We _could_ then at a later "fix" these drivers which are using
> > > vm_insert_range_buggy() to behave according to the normal vm_pgoff
> > > offsetting simply by removing the _buggy suffix on the function
> > > name and if that causes regressions, it gives us an easy way to revert.
> > >
> > > Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> > > Suggested-by: Russell King <linux@xxxxxxxxxxxxxxx>
> > > Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > > ---
> > >  include/linux/mm.h |  4 +++
> > >  mm/memory.c        | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  mm/nommu.c         | 14 ++++++++++
> > >  3 files changed, 99 insertions(+)
> > >
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index 80bb640..25752b0 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -2565,6 +2565,10 @@ unsigned long change_prot_numa(struct vm_area_struct *vma,
> > >  int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
> > >                       unsigned long pfn, unsigned long size, pgprot_t);
> > >  int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
> > > +int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> > > +                             unsigned long num);
> > > +int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
> > > +                             unsigned long num);
> > >  vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
> > >                       unsigned long pfn);
> > >  vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
> > > diff --git a/mm/memory.c b/mm/memory.c
> > > index e11ca9d..0a4bf57 100644
> > > --- a/mm/memory.c
> > > +++ b/mm/memory.c
> > > @@ -1520,6 +1520,87 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
> > >  }
> > >  EXPORT_SYMBOL(vm_insert_page);
> > >
> > > +/**
> > > + * __vm_insert_range - insert range of kernel pages into user vma
> > > + * @vma: user vma to map to
> > > + * @pages: pointer to array of source kernel pages
> > > + * @num: number of pages in page array
> > > + * @offset: user's requested vm_pgoff
> > > + *
> > > + * This allows drivers to insert range of kernel pages they've allocated
> > > + * into a user vma.
> > > + *
> > > + * If we fail to insert any page into the vma, the function will return
> > > + * immediately leaving any previously inserted pages present.  Callers
> > > + * from the mmap handler may immediately return the error as their caller
> > > + * will destroy the vma, removing any successfully inserted pages. Other
> > > + * callers should make their own arrangements for calling unmap_region().
> > > + *
> > > + * Context: Process context.
> > > + * Return: 0 on success and error code otherwise.
> > > + */
> > > +static int __vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> > > +                             unsigned long num, unsigned long offset)
> > > +{
> > > +     unsigned long count = vma_pages(vma);
> > > +     unsigned long uaddr = vma->vm_start;
> > > +     int ret, i;
> > > +
> > > +     /* Fail if the user requested offset is beyond the end of the object */
> > > +     if (offset > num)
> > > +             return -ENXIO;
> > > +
> > > +     /* Fail if the user requested size exceeds available object size */
> > > +     if (count > num - offset)
> > > +             return -ENXIO;
> > > +
> > > +     for (i = 0; i < count; i++) {
> > > +             ret = vm_insert_page(vma, uaddr, pages[offset + i]);
> > > +             if (ret < 0)
> > > +                     return ret;
> > > +             uaddr += PAGE_SIZE;
> > > +     }
> > > +
> > > +     return 0;
> > > +}
> > > +
> > > +/**
> > > + * vm_insert_range - insert range of kernel pages starts with non zero offset
> > > + * @vma: user vma to map to
> > > + * @pages: pointer to array of source kernel pages
> > > + * @num: number of pages in page array
> > > + *
> > > + * Maps an object consisting of `num' `pages', catering for the user's
> > > + * requested vm_pgoff
> > > + *
> >
> > The elaborate description you've added to __vm_insert_range() is better put
> > here, as this is the "public" function.
> 
> Ok, will add it in v3. Which means __vm_insert_range() still needs a short
> description ?

It won't hurt ;-)

> >
> > > + * Context: Process context. Called by mmap handlers.
> > > + * Return: 0 on success and error code otherwise.
> > > + */
> > > +int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> > > +                             unsigned long num)
> > > +{
> > > +     return __vm_insert_range(vma, pages, num, vma->vm_pgoff);
> > > +}
> > > +EXPORT_SYMBOL(vm_insert_range);
> > > +
> > > +/**
> > > + * vm_insert_range_buggy - insert range of kernel pages starts with zero offset
> > > + * @vma: user vma to map to
> > > + * @pages: pointer to array of source kernel pages
> > > + * @num: number of pages in page array
> > > + *
> > > + * Maps a set of pages, always starting at page[0]
> >
> > Here I'd add something like:
> >
> > Similar to vm_insert_range(), except that it explicitly sets @vm_pgoff to
> > 0. This function is intended for the drivers that did not consider
> > @vm_pgoff.
> 
> Ok.
> 
> >
> > > vm_insert_range_buggy() is the API which could be used to map
> > > range of kernel memory/pages in drivers which has not considered
> > > vm_pgoff. vm_pgoff is passed default as 0 for those drivers.
> >
> > > + *
> > > + * Context: Process context. Called by mmap handlers.
> > > + * Return: 0 on success and error code otherwise.
> > > + */
> > > +int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
> > > +                             unsigned long num)
> > > +{
> > > +     return __vm_insert_range(vma, pages, num, 0);
> > > +}
> > > +EXPORT_SYMBOL(vm_insert_range_buggy);
> > > +
> > >  static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
> > >                       pfn_t pfn, pgprot_t prot, bool mkwrite)
> > >  {
> > > diff --git a/mm/nommu.c b/mm/nommu.c
> > > index 749276b..21d101e 100644
> > > --- a/mm/nommu.c
> > > +++ b/mm/nommu.c
> > > @@ -473,6 +473,20 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
> > >  }
> > >  EXPORT_SYMBOL(vm_insert_page);
> > >
> > > +int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> > > +                     unsigned long num)
> > > +{
> > > +     return -EINVAL;
> > > +}
> > > +EXPORT_SYMBOL(vm_insert_range);
> > > +
> > > +int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
> > > +                             unsigned long num)
> > > +{
> > > +     return -EINVAL;
> > > +}
> > > +EXPORT_SYMBOL(vm_insert_range_buggy);
> > > +
> > >  /*
> > >   *  sys_brk() for the most part doesn't need the global kernel
> > >   *  lock, except when an application is doing something nasty
> > > --
> > > 1.9.1
> > >
> >
> > --
> > Sincerely yours,
> > Mike.
> >
> 

-- 
Sincerely yours,
Mike.