linux-kernel - Re: [PATCH v2 1/2] iommu: Prevent RESV_DIRECT devices from blocking domains

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Message-ID: <ZLqf3Q6zlnMi+woU@nvidia.com>
Date:   Fri, 21 Jul 2023 12:10:21 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Nicolin Chen <nicolinc@...dia.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] iommu: Prevent RESV_DIRECT devices from blocking
 domains

On Fri, Jul 21, 2023 at 03:07:47AM +0000, Tian, Kevin wrote:
> > @@ -974,13 +972,17 @@ static int
> > iommu_create_device_direct_mappings(struct iommu_domain *domain,
> >  		dma_addr_t start, end, addr;
> >  		size_t map_size = 0;
> > 
> > +		if (entry->type == IOMMU_RESV_DIRECT)
> > +			dev->iommu->requires_direct = 1;
> > +
> > +		if ((entry->type != IOMMU_RESV_DIRECT &&
> > +		     entry->type != IOMMU_RESV_DIRECT_RELAXABLE) ||
> > +		    !iommu_is_dma_domain(domain))
> > +			continue;
> 
> piggybacking a device attribute detection in a function which tries to
> populate domain mappings is a bit confusing.

It is, but to do otherwise we'd want to have the caller obtain the
reserved regions list and iterate it twice. Not sure it is worth the
trouble right now.

Jason