linux-kernel - RE: [PATCH 0/9] iommu/amd: Add AMD IOMMU emulation support for SEV-SNP guest kernel

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Message-ID:
 <SN6PR02MB4157E795C636EBE75CC806A1D4E22@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Mon, 13 May 2024 20:05:31 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, "joro@...tes.org"
	<joro@...tes.org>
CC: "thomas.lendacky@....com" <thomas.lendacky@....com>,
	"vasant.hegde@....com" <vasant.hegde@....com>, "michael.roth@....com"
	<michael.roth@....com>, "jon.grimm@....com" <jon.grimm@....com>,
	"rientjes@...gle.com" <rientjes@...gle.com>
Subject: RE: [PATCH 0/9] iommu/amd: Add AMD IOMMU emulation support for
 SEV-SNP guest kernel

From: Suravee Suthikulpanit <suravee.suthikulpanit@....com> Sent: Tuesday, April 30, 2024 8:24 AM
> 
> To boot a VM w/ x2APIC ID > 255, guest interrupt remapping emulation
> is required.

Top-level question:  Is there a reason the MSI extended destination ID mechanism is
insufficient to avoid the need for interrupt remapping?  (see function pointer
"msi_ext_dest_id").  I'm unclear on whether it is or not. If it is not sufficient, perhaps
you could explain why.

> For SEV guest, this can be achieved using an emulated
> AMD IOMMU.

You've used "SEV" here and in several other places.  I think you intend this to be
the more specific "SEV-SNP", and exclude SEV and SEV-ES. For avoid any confusion,
I'd suggest using "SEV-SNP" throughout if that's what you mean.

Michael

> 
> In order to support emulated AMD IOMMU in SEV guest, memory pages used
> by the guest IOMMU data structures must be in decrypted mode. Also GPAs
> for these pages must not have the memory encryption bit set.
> 
> Testing:
>   - Booting Linux SEV guest w/ 512 vcpus w/ QEMU emulated amd-iommu with
>     qemu-system-x86_64 option: -device amd-iommu,intremap=on,xtsup=on
>     (emulated devices only for now).
> 
> GIT repos:
> * https://github.com/AMDESE/linux-iommu/tree/iommu_next_sev-iommu-v1
> 
> Thanks,
> Suravee
> 
> Suravee Suthikulpanit (9):
>   iommu/amd: Introduce helper functions for managing IOMMU memory
>   iommu/amd: Convert Device Table pointer to use struct amd_iommu_mem
>   iommu/amd: Convert Command Buffer pointer to use struct amd_iommu_mem
>   iommu/amd: Convert Completion-Wait Semaphore pointer to use struct
>     amd_iommu_mem
>   iommu/amd: Convert Event Log pointer to use struct amd_iommu_mem
>   iommu/amd: Convert PPR Log pointer to use the struct amd_iommu_mem
>   iommu/amd: Remove iommu_alloc_4k_pages() helper function
>   iommu/amd: Decrypt interrupt remapping table for AMD IOMMU emulation
>     in SEV guest
>   iommu/amd: Set default domain to IDENTITY_DOMAIN when running in SEV
>     guest
> 
>  drivers/iommu/amd/amd_iommu.h       |  31 +++++-
>  drivers/iommu/amd/amd_iommu_types.h |  28 ++++--
>  drivers/iommu/amd/init.c            | 144 +++++++++++++++-------------
>  drivers/iommu/amd/iommu.c           | 133 +++++++++++++++++++------
>  drivers/iommu/amd/ppr.c             |  22 +++--
>  5 files changed, 246 insertions(+), 112 deletions(-)
> 
> --
> 2.34.1
>