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From: "Kalra, Ashish" <ashish.kalra@amd.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
	joro@8bytes.org, robin.murphy@arm.com, thomas.lendacky@amd.com,
	vasant.hegde@amd.com, jon.grimm@amd.com
Subject: Re: [PATCH 1/4] iommu/amd: Introduce Protection-domain flag VFIO
Date: Fri, 20 Jan 2023 13:55:38 -0600	[thread overview]
Message-ID: <da56ae0c-8f72-b39f-95b8-8870ec9fb336@amd.com> (raw)
In-Reply-To: <Y8rUYTjVhksAu+i9@ziepe.ca>

On 1/20/2023 11:50 AM, Jason Gunthorpe wrote:
> On Fri, Jan 20, 2023 at 11:01:21AM -0600, Kalra, Ashish wrote:
> 
>> We basically get the RMP #PF from the IOMMU because there is a page size
>> mismatch between the RMP table and the IOMMU page table. The RMP table's
>> large page entry has been smashed to 4K PTEs to handle page state change to
>> shared on 4K mappings, so this change has to be synced up with the IOMMU
>> page table, otherwise there is now a page size mismatch between RMP table
>> and IOMMU page table which causes the RMP #PF.
> 
> I understand that, you haven't answered my question:
> 
> Why is the IOMMU being programmed with pages it cannot access in the
> first place?
>

I believe the IOMMU page tables are setup as part of device pass-through 
to be able to do DMA to all of the guest memory, but i am not an IOMMU 
expert, so i will let Suravee elaborate on this.

Thanks,
Ashish

> Don't do that is the obvious solution there, and preserves huge page
> IO performance.
> 
> Jason
> 

  reply	other threads:[~2023-01-20 19:55 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-10 14:31 [PATCH 0/4] iommu/amd: Force SNP-enabled VFIO domain to 4K page size Suravee Suthikulpanit
2023-01-10 14:31 ` [PATCH 1/4] iommu/amd: Introduce Protection-domain flag VFIO Suravee Suthikulpanit
2023-01-11  3:31   ` kernel test robot
2023-01-13 15:33   ` Jason Gunthorpe
2023-01-19  8:54     ` Kalra, Ashish
2023-01-19 17:44       ` Jason Gunthorpe
2023-01-20 15:12         ` Kalra, Ashish
2023-01-20 16:13           ` Jason Gunthorpe
2023-01-20 17:01             ` Kalra, Ashish
2023-01-20 17:50               ` Jason Gunthorpe
2023-01-20 19:55                 ` Kalra, Ashish [this message]
2023-01-20 22:42                   ` Tom Lendacky
2023-01-21  0:09                     ` Jason Gunthorpe
2023-01-10 14:31 ` [PATCH 2/4] iommu/amd: Introduce structure amd_iommu_svm_ops.is_snp_guest() Suravee Suthikulpanit
2023-01-10 14:31 ` [PATCH 3/4] iommu: Introduce IOMMU call-back for processing struct KVM assigned to VFIO Suravee Suthikulpanit
2023-01-10 15:11   ` Robin Murphy
2023-01-17  4:20     ` Suthikulpanit, Suravee
2023-01-17 12:51       ` Robin Murphy
2023-01-13 15:35   ` Jason Gunthorpe
2023-01-17  5:31     ` Suthikulpanit, Suravee
2023-01-17 14:19       ` Jason Gunthorpe
2023-01-10 14:31 ` [PATCH 4/4] iommu/amd: Force SNP-enabled VFIO domain to 4K page size Suravee Suthikulpanit
2023-01-17 13:10   ` Eric van Tassell
2023-01-16 13:17 ` [PATCH 0/4] " Eric van Tassell

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