Re: [PATCH] vfio/iommu_type1: report the IOMMU aperture info

[Pierre Morel <pmorel@linux.vnet.ibm.com>]

On 30/11/2017 19:30, Alex Williamson wrote:
> On Thu, 30 Nov 2017 16:11:35 +0100
> Pierre Morel <pmorel@linux.vnet.ibm.com> wrote:
> 
>> On 30/11/2017 15:08, Alex Williamson wrote:
>>> On Thu, 30 Nov 2017 12:34:38 +0100
>>> Pierre Morel <pmorel@linux.vnet.ibm.com> wrote:
>>>    
>>>> When userland VFIO defines a new IOMMU for a guest it may
>>>> want to specify to the guest the physical limits of
>>>> the underlying host IOMMU to avoid access to forbidden
>>>> memory ranges.
>>>>
>>>> Currently, the vfio_iommu_type1 driver does not report this
>>>> information to userland.
>>>>
>>>> Let's extend the vfio_iommu_type1_info structure reported
>>>> by the ioctl VFIO_IOMMU_GET_INFO command to report the
>>>> IOMMU limits as new uint64_t entries aperture_start and
>>>> aperture_end.
>>>>
>>>> Let's also extend the flags bit map to add a flag specifying
>>>> if this extension of the info structure is reported or not.
>>>>
>>>> Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
>>>> ---
>>>>    drivers/vfio/vfio_iommu_type1.c | 42 +++++++++++++++++++++++++++++++++++++++++
>>>>    include/uapi/linux/vfio.h       |  3 +++
>>>>    2 files changed, 45 insertions(+)
>>>>
>>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>>>> index 8549cb1..7da5fe0 100644
>>>> --- a/drivers/vfio/vfio_iommu_type1.c
>>>> +++ b/drivers/vfio/vfio_iommu_type1.c
>>>> @@ -1526,6 +1526,40 @@ static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
>>>>    	return ret;
>>>>    }
>>>>    
>>>> +/**
>>>> + * vfio_get_aperture - report minimal aperture of a vfio_iommu
>>>> + * @iommu: the current vfio_iommu
>>>> + * @start: a pointer to the aperture start
>>>> + * @end  : a pointer to the aperture end
>>>> + *
>>>> + * This function iterate on the domains using the given vfio_iommu
>>>> + * and restrict the aperture to the minimal aperture common
>>>> + * to all domains sharing this vfio_iommu.
>>>> + */
>>>> +static void vfio_get_aperture(struct vfio_iommu *iommu, uint64_t *start,
>>>> +				uint64_t *end)
>>>> +{
>>>> +	struct iommu_domain_geometry geometry;
>>>> +	struct vfio_domain *domain;
>>>> +
>>>> +	*start = 0;
>>>> +	*end = U64_MAX;
>>>> +
>>>> +	mutex_lock(&iommu->lock);
>>>> +	/* loop on all domains using this vfio_iommu */
>>>> +	list_for_each_entry(domain, &iommu->domain_list, next) {
>>>> +		iommu_domain_get_attr(domain->domain, DOMAIN_ATTR_GEOMETRY,
>>>> +					&geometry);
>>>> +		if (geometry.force_aperture) {
>>>> +			if (geometry.aperture_start > *start)
>>>> +				*start = geometry.aperture_start;
>>>> +			if (geometry.aperture_end < *end)
>>>> +				*end = geometry.aperture_end;
>>>> +		}
>>>> +	}
>>>> +	mutex_unlock(&iommu->lock);
>>>> +}
>>>> +
>>>>    static long vfio_iommu_type1_ioctl(void *iommu_data,
>>>>    				   unsigned int cmd, unsigned long arg)
>>>>    {
>>>> @@ -1560,6 +1594,14 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>>>    
>>>>    		info.iova_pgsizes = vfio_pgsize_bitmap(iommu);
>>>>    
>>>> +		minsz = min_t(size_t, info.argsz, sizeof(info));
>>>> +		if (minsz >= offsetofend(struct vfio_iommu_type1_info,
>>>> +					 aperture_end)) {
>>>> +			info.flags |= VFIO_IOMMU_INFO_APERTURE;
>>>> +			vfio_get_aperture(iommu, &info.aperture_start,
>>>> +					  &info.aperture_end);
>>>> +		}
>>>> +
>>>>    		return copy_to_user((void __user *)arg, &info, minsz) ?
>>>>    			-EFAULT : 0;
>>>>    
>>>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>>>> index 0fb25fb..780d909 100644
>>>> --- a/include/uapi/linux/vfio.h
>>>> +++ b/include/uapi/linux/vfio.h
>>>> @@ -519,6 +519,9 @@ struct vfio_iommu_type1_info {
>>>>    	__u32	flags;
>>>>    #define VFIO_IOMMU_INFO_PGSIZES (1 << 0)	/* supported page sizes info */
>>>>    	__u64	iova_pgsizes;		/* Bitmap of supported page sizes */
>>>> +#define VFIO_IOMMU_INFO_APERTURE (1 << 1)	/* supported aperture info */
>>>> +	__u64   aperture_start;		/* start of DMA aperture */
>>>> +	__u64   aperture_end;		/* end of DMA aperture */
>>>>    };
>>>>    
>>>>    #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
>>>
>>> This only supports the most simple topology, even x86 cannot claim to
>>> have a single contiguous aperture, it's typically bisected by an MSI
>>> window.  I think we need an API that supports one or more apertures
>>> out of the box.  Also as Eric indicates, a capability is probably the
>>> better option for creating a flexible structure.  Thanks,
>>>
>>> Alex
>>>    
>>
>>
>> Yes, I understand that a capability here is a must, I will follow this way.
>>
>> For having multiple aperture and MSI protection, I understood it was
>> done using windows and reserved regions.
>> Can you point me to my error?
> 
> See the thread from Huawei, I don't think that's a solved problem:
> 
> https://lists.gnu.org/archive/html/qemu-arm/2017-11/msg00237.html
> 
> If you want sysfs to be consumed separately by the user and fed into
> new QEMU command line options for creating a VM layout, perhaps that's
> sufficient, but I think the vfio api for the iommu should encompass
> describing available ranges of mappable iova space without cobbling
> together arbitrary info from sysfs.  Thanks,
> 
> Alex
> 

Hi Alex,

I resume to see if I understood you well:

We may have physical IOMMUs with a more complex access that can not be 
specified by only defining the start and end of a read/write region.

Windows can be used to reserve regions for the VM but it is not what we 
want. What we want is to know what the host can offer which is a mix of 
aperture and windows.

To report this we can use capabilities in a positive way, describing 
what the host offers not what it can not provide.

To achieve this we have to use two interfaces:
- VFIO user interface with VFIO_IOMMU_GET_INFO and capabilities
- Physical IOMMU interface with both geometry and window iommu_ops 
callbacks.

If it is sufficiently near from what you thought I will provide a new 
version in this direction.

Regards,

Pierre



-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany