linux-kernel - RE: [PATCH v3 04/10] iommu/vt-d: Add helper to setup pasid nested translation

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Date:   Wed, 7 Jun 2023 08:34:22 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "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>
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>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: RE: [PATCH v3 04/10] iommu/vt-d: Add helper to setup pasid nested
 translation

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Friday, May 26, 2023 12:16 PM

> >> +
> >> +	/* First level PGD (in GPA) must be supported by the second level. */
> >> +	if ((uintptr_t)s1_gpgd > (1ULL << s2_domain->gaw)) {
> >> +		dev_err_ratelimited(dev,
> >> +				    "Guest PGD %lx not supported,
> >> max %llx\n",
> >> +				    (uintptr_t)s1_gpgd, s2_domain-
> >>> max_addr);
> >> +		return -EINVAL;
> >> +	}
> >
> > I'm not sure how useful this check is. Even if the pgd is sane the
> > lower level PTEs could include unsupported GPA's. If a guest really
> > doesn't want to follow the GPA restriction which vIOMMU reports,
> > it can easily cause IOMMU fault in many ways.
> 
> You are right.
> 
> > Then why treating pgd specially?
> 
> I have no memory about this check for now. Yi, any thought?

I don’t think there is another special reason. Just want to ensure the page table
base address follows the GPA restriction. But as Kevin mentioned, hw can detect
it anyway. So, I think this check can be dropped.

Regards,
Yi Liu