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

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Date:   Thu, 30 Nov 2017 15:17:36 +0100
From:   Pierre Morel <pmorel@...ux.vnet.ibm.com>
To:     Auger Eric <eric.auger@...hat.com>, alex.williamson@...hat.com
Cc:     cohuck@...hat.com, borntraeger@...ibm.com,
        zyimin@...ux.vnet.ibm.com, pasic@...ux.vnet.ibm.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio/iommu_type1: report the IOMMU aperture info

On 30/11/2017 14:22, Auger Eric wrote:
> Hi Pierre,
> On 30/11/17 12:34, Pierre Morel 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@...ux.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)
>>
> 
> In the past I was told by Alex that using the capability chain
> extensions to add some new capabilities was a better approach:
> 
> https://lkml.org/lkml/2016/4/6/751
> 
> I did that kind of exercise in
> [PATCH v9 7/7] vfio/type1: return MSI geometry through
> VFIO_IOMMU_GET_INFO capability chains
> 
> https://lists.linuxfoundation.org/pipermail/iommu/2016-May/016892.html
> 
> The patch was not used eventually but maybe that can help.
> 
> Thanks
> 
> Eric
> 

indeed interesting, I will go this way.
Thanks and also thanks for the pointers.

Pierre

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