linux-kernel - RE: [PATCH 1/1] iommu/vt-d: Make context clearing consistent with context mapping

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Message-ID: <BN9PR11MB5276C809A2BF1A63B92F09EA8CB2A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Tue, 14 Nov 2023 04:46:23 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Will Deacon" <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Jason Gunthorpe" <jgg@...pe.ca>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/1] iommu/vt-d: Make context clearing consistent with
 context mapping

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, November 14, 2023 11:22 AM
> 
> On 11/14/23 11:20 AM, Tian, Kevin wrote:
> >> From: Lu Baolu <baolu.lu@...ux.intel.com>
> >> Sent: Tuesday, November 14, 2023 9:11 AM
> >>
> >> In the iommu probe_device path, domain_context_mapping() allows
> setting
> >> up the context entry for a non-PCI device. However, in the iommu
> >> release_device path, domain_context_clear() only clears context entries
> >> for PCI devices.
> >>
> >> Make domain_context_clear() behave consistently with
> >> domain_context_mapping() by clearing context entries for both PCI and
> >> non-PCI devices.
> >>
> >> Fixes: 579305f75d34 ("iommu/vt-d: Update to use PCI DMA aliases")
> >> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> >
> > The code before the fix tag also has the same problem. If we really want
> > backport then let's find out the very first commit which exhibits this
> > problem.
> 
> Commit 579305f75d34 allows non-PCI devices.
> 
> +       if (!dev_is_pci(dev))
> +               return domain_context_mapping_one(domain, iommu, bus, devfn,
>                                                    translation);
> +
> +       data.domain = domain;
> +       data.iommu = iommu;
> +       data.translation = translation;
> +
> +       return pci_for_each_dma_alias(to_pci_dev(dev),
> +                                     &domain_context_mapping_cb, &data);
> 
> But it forgot to update the domain_context_clear() helper. So this is
> actually a fix for that commit.

thanks. I didn't note that side effect from commit msg.

> 
> >
> > But I wonder the actual impact w/o such fix. If there is no hot-remove
> > possible for those non-PCI devices the context entry will be leaved
> > enabled until the machine is off. Then this fix is nice-to-have then
> > probably no need to backport?
> 
> It doesn't cause real issues as far as I can see. So there's no need to
> back port it to stable kernels. That's the reason I didn't add cc-stable
> tag. But we still need a fix tag as it's actually a fix.
> 

make sense.

Reviewed-by: Kevin Tian <kevin.tian@...el.com>