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Message-ID: <CAFqt6za9xA_8OKiaaHXcO9go+RtPdjLY5Bz_fgQL+DZbermNhA@mail.gmail.com>
Date: Thu, 7 Feb 2019 21:19:47 +0530
From: Souptick Joarder <jrdr.linux@...il.com>
To: Mike Rapoport <rppt@...ux.ibm.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
Michal Hocko <mhocko@...e.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
vbabka@...e.cz, Rik van Riel <riel@...riel.com>,
Stephen Rothwell <sfr@...b.auug.org.au>,
rppt@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>,
Russell King - ARM Linux <linux@...linux.org.uk>,
robin.murphy@....com, iamjoonsoo.kim@....com, treding@...dia.com,
Kees Cook <keescook@...omium.org>,
Marek Szyprowski <m.szyprowski@...sung.com>,
stefanr@...6.in-berlin.de, hjc@...k-chips.com,
Heiko Stuebner <heiko@...ech.de>, airlied@...ux.ie,
oleksandr_andrushchenko@...m.com, joro@...tes.org,
pawel@...iak.com, Kyungmin Park <kyungmin.park@...sung.com>,
mchehab@...nel.org, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
Linux-MM <linux-mm@...ck.org>,
linux-arm-kernel@...ts.infradead.org,
linux1394-devel@...ts.sourceforge.net,
dri-devel@...ts.freedesktop.org,
linux-rockchip@...ts.infradead.org, xen-devel@...ts.xen.org,
iommu@...ts.linux-foundation.org, linux-media@...r.kernel.org
Subject: Re: [PATCHv2 1/9] mm: Introduce new vm_insert_range and
vm_insert_range_buggy API
Hi Mike,
On Thu, Jan 31, 2019 at 2:09 PM Mike Rapoport <rppt@...ux.ibm.com> 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@...il.com>
> > Suggested-by: Russell King <linux@...linux.org.uk>
> > Suggested-by: Matthew Wilcox <willy@...radead.org>
> > ---
> > 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.
>
> > + * 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.
Just thought to take opinion for documentation before placing it in v3.
Does it looks fine ?
+/**
+ * __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 allow drivers to insert range of kernel pages into a user vma.
+ *
+ * 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)
+/**
+ * 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
+ *
+ * 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. 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)
+/**
+ * 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
+ *
+ * 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.
+ *
+ * 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)
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