linux-kernel - Re: [PATCH 10/13] PCI: revoke mappings like devmem

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Date:   Wed, 7 Oct 2020 21:24:49 +0200
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Linux MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>, linux-s390@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kees Cook <keescook@...omium.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 10/13] PCI: revoke mappings like devmem

On Wed, Oct 7, 2020 at 8:41 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> Capitalize subject, like other patches in this series and previous
> drivers/pci history.
>
> On Wed, Oct 07, 2020 at 06:44:23PM +0200, Daniel Vetter wrote:
> > Since 3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims
> > the region") /dev/kmem zaps ptes when the kernel requests exclusive
> > acccess to an iomem region. And with CONFIG_IO_STRICT_DEVMEM, this is
> > the default for all driver uses.
> >
> > Except there's two more ways to access pci bars: sysfs and proc mmap
> > support. Let's plug that hole.
>
> s/pci/PCI/ in commit logs and comments.
>
> > For revoke_devmem() to work we need to link our vma into the same
> > address_space, with consistent vma->vm_pgoff. ->pgoff is already
> > adjusted, because that's how (io_)remap_pfn_range works, but for the
> > mapping we need to adjust vma->vm_file->f_mapping. Usually that's done
> > at ->open time, but that's a bit tricky here with all the entry points
> > and arch code. So instead create a fake file and adjust vma->vm_file.
> >
> > Note this only works for ARCH_GENERIC_PCI_MMAP_RESOURCE. But that
> > seems to be a subset of architectures support STRICT_DEVMEM, so we
> > should be good.
> >
> > The only difference in access checks left is that sysfs pci mmap does
> > not check for CAP_RAWIO. But I think that makes some sense compared to
> > /dev/mem and proc, where one file gives you access to everything and
> > no ownership applies.
>
> > --- a/drivers/char/mem.c
> > +++ b/drivers/char/mem.c
> > @@ -810,6 +810,7 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
> >  }
> >
> >  static struct inode *devmem_inode;
> > +static struct vfsmount *devmem_vfs_mount;
> >
> >  #ifdef CONFIG_IO_STRICT_DEVMEM
> >  void revoke_devmem(struct resource *res)
> > @@ -843,6 +844,20 @@ void revoke_devmem(struct resource *res)
> >
> >       unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
> >  }
> > +
> > +struct file *devmem_getfile(void)
> > +{
> > +     struct file *file;
> > +
> > +     file = alloc_file_pseudo(devmem_inode, devmem_vfs_mount, "devmem",
> > +                              O_RDWR, &kmem_fops);
> > +     if (IS_ERR(file))
> > +             return NULL;
> > +
> > +     file->f_mapping = devmem_indoe->i_mapping;
>
> "devmem_indoe"?  Obviously not compiled, I guess?

Yeah apologies, I forgot to compile this with CONFIG_IO_STRICT_DEVMEM
set. The entire series is more rfc about the overall problem really, I
need to also figure out how to even this this somehow. I guess there's
nothing really ready made here?
-Daniel

> > --- a/include/linux/ioport.h
> > +++ b/include/linux/ioport.h
> > @@ -304,8 +304,10 @@ struct resource *request_free_mem_region(struct resource *base,
> >
> >  #ifdef CONFIG_IO_STRICT_DEVMEM
> >  void revoke_devmem(struct resource *res);
> > +struct file *devm_getfile(void);
> >  #else
> >  static inline void revoke_devmem(struct resource *res) { };
> > +static inline struct file *devmem_getfile(void) { return NULL; };
>
> I guess these names are supposed to match?
>
> >  #endif
> >
> >  #endif /* __ASSEMBLY__ */
> > --
> > 2.28.0
> >



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch