netdev - Re: [PATCH 7/8] iommu/intel: Support the gfp argument to the map

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y8aijhHjqqf6hjwL@nvidia.com>
Date:   Tue, 17 Jan 2023 09:28:46 -0400
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>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "ath10k@...ts.infradead.org" <ath10k@...ts.infradead.org>,
        "ath11k@...ts.infradead.org" <ath11k@...ts.infradead.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-remoteproc@...r.kernel.org" <linux-remoteproc@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 7/8] iommu/intel: Support the gfp argument to the
 map_pages op

On Tue, Jan 17, 2023 at 03:38:51AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Saturday, January 7, 2023 12:43 AM
> > 
> > @@ -2368,7 +2372,7 @@ static int iommu_domain_identity_map(struct
> > dmar_domain *domain,
> > 
> >  	return __domain_mapping(domain, first_vpfn,
> >  				first_vpfn, last_vpfn - first_vpfn + 1,
> > -				DMA_PTE_READ|DMA_PTE_WRITE);
> > +				DMA_PTE_READ|DMA_PTE_WRITE,
> > GFP_KERNEL);
> >  }
> 
> Baolu, can you help confirm whether switching from GFP_ATOMIC to
> GFP_KERNEL is OK in this path? it looks fine to me in a quick glance
> but want to be conservative here.

I checked it carefully myself as well, good to check again.

> > @@ -4333,7 +4337,8 @@ static size_t intel_iommu_unmap(struct
> > iommu_domain *domain,
> > 
> >  	/* Cope with horrid API which requires us to unmap more than the
> >  	   size argument if it happens to be a large-page mapping. */
> > -	BUG_ON(!pfn_to_dma_pte(dmar_domain, iova >> VTD_PAGE_SHIFT,
> > &level));
> > +	BUG_ON(!pfn_to_dma_pte(dmar_domain, iova >> VTD_PAGE_SHIFT,
> > &level,
> > +			       GFP_ATOMIC));
> 
> with level==0 it implies it's only lookup w/o pgtable allocation. From this
> angle it reads better to use a more relaxed gfp e.g. GFP_KERNEL here.

We should only write GFP_KERNEL if it is actually a sleepable context
because it will be mighty confusing if it isn't. I couldn't tell what
the context is so I left it as ATOMIC.

You are correct this is only just a lookup and so the value is never
used / doesn't matter.

Jason