linux-kernel - Re: [PATCH v8 02/10] iommu/vt-d: Add nested translation helper function

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Date:   Fri, 10 Jan 2020 09:15:45 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        Eric Auger <eric.auger@...hat.com>,
        Yi L <yi.l.liu@...ux.intel.com>
Subject: Re: [PATCH v8 02/10] iommu/vt-d: Add nested translation helper
 function

Hi Jacob,

On 1/10/20 2:39 AM, Jacob Pan wrote:
> On Wed, 18 Dec 2019 10:41:53 +0800
> Lu Baolu <baolu.lu@...ux.intel.com> wrote:
> 
>> Hi again,
>>
>> On 12/17/19 3:24 AM, Jacob Pan wrote:
>>> +/**
>>> + * intel_pasid_setup_nested() - Set up PASID entry for nested
>>> translation
>>> + * which is used for vSVA. The first level page tables are used for
>>> + * GVA-GPA or GIOVA-GPA translation in the guest, second level
>>> page tables
>>> + *  are used for GPA-HPA translation.
>>> + *
>>> + * @iommu:      Iommu which the device belong to
>>> + * @dev:        Device to be set up for translation
>>> + * @gpgd:       FLPTPTR: First Level Page translation pointer in
>>> GPA
>>> + * @pasid:      PASID to be programmed in the device PASID table
>>> + * @pasid_data: Additional PASID info from the guest bind request
>>> + * @domain:     Domain info for setting up second level page tables
>>> + * @addr_width: Address width of the first level (guest)
>>> + */
>>> +int intel_pasid_setup_nested(struct intel_iommu *iommu,
>>> +			struct device *dev, pgd_t *gpgd,
>>> +			int pasid, struct
>>> iommu_gpasid_bind_data_vtd *pasid_data,
>>> +			struct dmar_domain *domain,
>>> +			int addr_width)
>>> +{
>>> +	struct pasid_entry *pte;
>>> +	struct dma_pte *pgd;
>>> +	u64 pgd_val;
>>> +	int agaw;
>>> +	u16 did;
>>> +
>>> +	if (!ecap_nest(iommu->ecap)) {
>>> +		pr_err("IOMMU: %s: No nested translation
>>> support\n",
>>> +		       iommu->name);
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	pte = intel_pasid_get_entry(dev, pasid);
>>> +	if (WARN_ON(!pte))
>>> +		return -EINVAL;
>>> +
>>> +	pasid_clear_entry(pte);
>>
>> In some cases, e.g. nested mode for GIOVA-HPA, the PASID entry might
>> have already been setup for second level translation. (This could be
>> checked with the Present bit.) Hence, it's safe to flush caches here.
>>
>> Or, maybe intel_pasid_tear_down_entry() is more suitable?
>>
> We don't allow binding the same device-PASID twice, so if the PASID
> entry was used for GIOVA/RID2PASID, it should unbind first, and
> teardown flush included, right?
> 

Fair enough. Can you please add this as a comment to this function? So
that the caller of this interface can know this. Or add a check in this
function which returns error if the pasid entry has already been bond.

Best regards,
baolu