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

[Souptick Joarder <jrdr.linux@xxxxxxxxx>]

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 ?
>
> > + * 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.
>

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