linux-kernel - Re: [RFC PATCH v5 08/11] VFIO_PLATFORM: Support MMAP of MMIO regions

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Date:	Tue, 29 Apr 2014 15:28:43 +0200
From:	Antonios Motakis <a.motakis@...tualopensystems.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	kvm-arm <kvmarm@...ts.cs.columbia.edu>,
	Linux IOMMU <iommu@...ts.linux-foundation.org>,
	VirtualOpenSystems Technical Team <tech@...tualopensystems.com>,
	alvise rigo <a.rigo@...tualopensystems.com>,
	KVM devel mailing list <kvm@...r.kernel.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Kim Phillips <kim.phillips@...escale.com>,
	Stuart Yoder <stuart.yoder@...escale.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v5 08/11] VFIO_PLATFORM: Support MMAP of MMIO regions

On Mon, Apr 28, 2014 at 7:27 PM, Alex Williamson
<alex.williamson@...hat.com> wrote:
> On Mon, 2014-04-28 at 17:52 +0200, Antonios Motakis wrote:
>> Allow to memory map the MMIO regions of the device so userspace can
>> directly access them.
>>
>> Signed-off-by: Antonios Motakis <a.motakis@...tualopensystems.com>
>> ---
>>  drivers/vfio/platform/vfio_platform.c | 40 ++++++++++++++++++++++++++++++++++-
>>  1 file changed, 39 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/platform/vfio_platform.c b/drivers/vfio/platform/vfio_platform.c
>> index 7c01ced..37beff3 100644
>> --- a/drivers/vfio/platform/vfio_platform.c
>> +++ b/drivers/vfio/platform/vfio_platform.c
>> @@ -58,6 +58,11 @@ static int vfio_platform_regions_init(struct vfio_platform_device *vdev)
>>               region.flags = VFIO_REGION_INFO_FLAG_READ
>>                               | VFIO_REGION_INFO_FLAG_WRITE;
>>
>> +             /* Only regions addressed with PAGE granularity can be MMAPed
>> +              * securely. */
>> +             if (!(region.addr & ~PAGE_MASK) && !(region.size & ~PAGE_MASK))
>> +                     region.flags |= VFIO_REGION_INFO_FLAG_MMAP;
>> +
>
> Ok, so the security is only that we need page alignment.  Maybe that
> could be made more clear in the previous patch.  PCI has regions like
> the MSI-X table that we need to protect from userspace access beyond
> page alignment requirements.  Thanks,

Ack, I will make the previous description more clear.

>
> Alex
>
>>               vdev->region[i] = region;
>>       }
>>
>> @@ -268,7 +273,40 @@ err:
>>
>>  static int vfio_platform_mmap(void *device_data, struct vm_area_struct *vma)
>>  {
>> -     return -EINVAL;
>> +     struct vfio_platform_device *vdev = device_data;
>> +     unsigned int index;
>> +     u64 req_len, pgoff, req_start;
>> +     struct vfio_platform_region region;
>> +
>> +     index = vma->vm_pgoff >> (VFIO_PLATFORM_OFFSET_SHIFT - PAGE_SHIFT);
>> +
>> +     if (vma->vm_end < vma->vm_start)
>> +             return -EINVAL;
>> +     if ((vma->vm_flags & VM_SHARED) == 0)
>> +             return -EINVAL;
>> +     if (index >= vdev->num_regions)
>> +             return -EINVAL;
>> +     if (vma->vm_start & ~PAGE_MASK)
>> +             return -EINVAL;
>> +     if (vma->vm_end & ~PAGE_MASK)
>> +             return -EINVAL;
>> +
>> +     region = vdev->region[index];
>> +
>> +     req_len = vma->vm_end - vma->vm_start;
>> +     pgoff = vma->vm_pgoff &
>> +             ((1U << (VFIO_PLATFORM_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
>> +     req_start = pgoff << PAGE_SHIFT;
>> +
>> +     if (region.size < PAGE_SIZE || req_start + req_len > region.size)
>> +             return -EINVAL;
>> +
>> +     vma->vm_private_data = vdev;
>> +     vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>> +     vma->vm_pgoff = (region.addr >> PAGE_SHIFT) + pgoff;
>> +
>> +     return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
>> +                            req_len, vma->vm_page_prot);
>>  }
>>
>>  static const struct vfio_device_ops vfio_platform_ops = {
>
>
>



-- 
Antonios Motakis
Virtual Open Systems
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