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

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Date:   Wed, 7 Oct 2020 13:41:31 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, 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@...r.kernel.org
Subject: Re: [PATCH 10/13] PCI: revoke mappings like devmem

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?

> --- 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
>