From: Baolu Lu <baolu.lu@linux.intel.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: baolu.lu@linux.intel.com, Robin Murphy <robin.murphy@arm.com>,
joro@8bytes.org, will@kernel.org, ewagner12@gmail.com,
suravee.suthikulpanit@amd.com, vashegde@amd.com,
iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
regressions@lists.linux.dev
Subject: Re: [PATCH] iommu: Fix def_domain_type interaction with untrusted devices
Date: Thu, 25 Apr 2024 09:41:44 +0800 [thread overview]
Message-ID: <7648b859-3685-41d7-a7b9-e137441c98a0@linux.intel.com> (raw)
In-Reply-To: <20240424143702.GH231144@ziepe.ca>
On 4/24/24 10:37 PM, Jason Gunthorpe wrote:
> On Wed, Apr 24, 2024 at 10:18:00PM +0800, Baolu Lu wrote:
>
>> For example, the intel iommu driver allows users to opt-in graphic in
>> passthrough mode, in that case def_domain_type will return
>> IOMMU_DOMAIN_IDENTITY no matter the device is trusted or not.
>>
>> if ((iommu_identity_mapping & IDENTMAP_GFX) && IS_GFX_DEVICE(pdev))
>> return IOMMU_DOMAIN_IDENTITY;
>>
>> this potentially creates same conflict as the amd driver.
> These performance policy choices should be done in the core code and
> they should interact correctly with other policy knobs like untrusted.
>
> If Intel Graphics has some performance reason to prefer IDENTITY then
> it should work the same no matter the IOMMU it is connected to. I
> think just because the GPU is co-packaged with the IOMMU isn't a good
> reason to organize the software like this.
>
> If having a policy of a performance boost to some devices is
> legitimate then I guess we'd need more levels on the command line:
> fast all IDENTITY
> fast-secure all DMA expect IDENTIY for special devices
> mostly-secure all DMA but unmapping is not strict
> secure all DMA and strict unmapping
>
> How exactly you decide when the performance reason justfies IDENTITY,
> I don't know.. Would mlx5 800G NICs that can overwhelm most IOMMUs
> also go in that bucket too?
>
> But yes, I'm quite adament that drivers should not be using
> def_domain_type as some kind of performance policy thing.
Yes. I will follow up to address this issue in the intel driver.
Best regards,
baolu
prev parent reply other threads:[~2024-04-25 1:43 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-16 13:00 [PATCH] iommu: Fix def_domain_type interaction with untrusted devices Robin Murphy
2024-04-16 14:33 ` Greg KH
2024-04-16 15:29 ` Jason Gunthorpe
2024-04-17 5:23 ` Vasant Hegde
2024-04-17 16:06 ` Jason Gunthorpe
2024-04-18 11:44 ` Vasant Hegde
2024-04-18 12:02 ` Jason Gunthorpe
2024-04-23 11:26 ` Robin Murphy
2024-04-24 13:04 ` Jason Gunthorpe
2024-04-24 14:05 ` Baolu Lu
2024-04-24 14:18 ` Baolu Lu
2024-04-24 14:37 ` Jason Gunthorpe
2024-04-25 1:41 ` Baolu Lu [this message]
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