Re: [RFC 3/7] iommufd: Add iommufd_device_bind_pasid()

[Yi Liu <yi.l.liu@intel.com>]

On 2023/11/8 16:46, Tian, Kevin wrote:
>> From: Liu, Yi L <yi.l.liu@intel.com>
>> Sent: Wednesday, November 8, 2023 3:45 PM
>>
>> On 2023/10/10 16:19, Tian, Kevin wrote:
>>>> From: Liu, Yi L <yi.l.liu@intel.com>
>>>> Sent: Monday, October 9, 2023 4:51 PM
>>>>
>>>> +struct iommufd_device *iommufd_device_bind_pasid(struct
>> iommufd_ctx
>>>> *ictx,
>>>> +						 struct device *dev,
>>>> +						 u32 pasid, u32 *id)
>>>> +{
>>>> +	struct iommufd_device *idev;
>>>> +	int rc;
>>>> +
>>>> +	/*
>>>> +	 * iommufd always sets IOMMU_CACHE because we offer no way for
>>>> userspace
>>>> +	 * to restore cache coherency.
>>>> +	 */
>>>> +	if (!device_iommu_capable(dev, IOMMU_CAP_CACHE_COHERENCY))
>>>> +		return ERR_PTR(-EINVAL);
>>>> +
>>>> +	/*
>>>> +	 * No iommu supports pasid-granular msi message today. Here we
>>>> +	 * just check whether the parent device can do safe interrupts.
>>>> +	 * Isolation between virtual devices within the parent device
>>>> +	 * relies on the parent driver to enforce.
>>>> +	 */
>>>> +	if (!iommufd_selftest_is_mock_dev(dev) &&
>>>> +	    !msi_device_has_isolated_msi(dev)) {
>>>> +		rc = iommufd_allow_unsafe_interrupts(dev);
>>>> +		if (rc)
>>>> +			return ERR_PTR(rc);
>>>> +	}
>>>> +
>>>
>>> Only MemWr w/o pasid can be interpreted as an interrupt message
>>> then we need msi isolation to protect.
>>
>> yes.
>>
>>>
>>> But for SIOV all MemWr's are tagged with a pasid hence can never
>>> trigger an interrupt. From this angle looks this check is unnecessary.
>>
>> But the interrupts out from a SIOV virtual device do not have pasid (at
>> least today). Seems still need a check here if we consider this bind for
>> a SIOV virtual device just like binding a physical device.
>>
> 
> this check assumes the device is trusted. as long as there is no way
> for malicious guest to generate arbitrary interrupt messages then
> it's fine.
> 
> for physical device a MemWr can be interpreted as interrupt so
> we need msi isolation.
> 
> for SIOV all MemWr has pasid then we don't have such worry.
> IMS is under host's control so interrupt messages are already
> sanitized.

sure. this makes sense to me now.:)

-- 
Regards,
Yi Liu