linux-kernel - Re: [RFC 3/7] iommufd: Add iommufd_device_bind

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Message-ID: <8aa35b4e-6bf1-461b-8d7a-5331dfdc3934@intel.com>
Date:   Wed, 8 Nov 2023 17:03:55 +0800
From:   Yi Liu <yi.l.liu@...el.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>,
        "Martins, Joao" <joao.m.martins@...cle.com>
Subject: Re: [RFC 3/7] iommufd: Add iommufd_device_bind_pasid()

On 2023/11/8 16:46, Tian, Kevin wrote:
>> From: Liu, Yi L <yi.l.liu@...el.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@...el.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