Re: [RFC PATCH v3 2/2] arm: kernel: fix pci_mmap_page_range() offset calculation

[Bjorn Helgaas <bhelgaas@google.com>]

On Thu, Nov 13, 2014 at 11:19:16AM +0000, Lorenzo Pieralisi wrote:
> The pci_mmap_page_range() API should be written to expect offset
> values representing PCI memory resource addresses as seen by user
> space, through the pci_resource_to_user() API.
> 
> ARM relies on the standard implementation of pci_resource_to_user()
> which actually is an identity map and exports to user space
> PCI memory resources as they are stored in PCI devices resources
> structures, which represent CPU physical addresses (fixed-up using
> BUS to CPU address conversions) not PCI bus addresses.
> 
> Therefore, on ARM platforms where the mapping between CPU and BUS
> address is not a 1:1 the current pci_mmap_page_range() implementation is
> erroneous, in that an additional shift is applied to an already fixed-up
> offset passed from userspace.
> 
> Hence, this patch removes the mem_offset from the pgoff calculation
> since the offset as passed from user space already represents the CPU
> physical address corresponding to the resource to be mapped, ie no
> additional offset should be applied.
> 
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Russell King <linux@arm.linux.org.uk>
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  arch/arm/kernel/bios32.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/kernel/bios32.c b/arch/arm/kernel/bios32.c
> index 17a26c1..b56fa2d 100644
> --- a/arch/arm/kernel/bios32.c
> +++ b/arch/arm/kernel/bios32.c
> @@ -626,21 +626,15 @@ int pcibios_enable_device(struct pci_dev *dev, int mask)
>  int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
>  			enum pci_mmap_state mmap_state, int write_combine)
>  {
> -	struct pci_sys_data *root = dev->sysdata;
> -	unsigned long phys;
> -
> -	if (mmap_state == pci_mmap_io) {
> +	if (mmap_state == pci_mmap_io)
>  		return -EINVAL;
> -	} else {
> -		phys = vma->vm_pgoff + (root->mem_offset >> PAGE_SHIFT);
> -	}
>  
>  	/*
>  	 * Mark this as IO
>  	 */
>  	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>  
> -	if (remap_pfn_range(vma, vma->vm_start, phys,
> +	if (remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
>  			     vma->vm_end - vma->vm_start,
>  			     vma->vm_page_prot))
>  		return -EAGAIN;
> -- 
> 2.1.2
> 
> --
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