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From: Michael Kelley <mhklinux@outlook.com>
To: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"iommu@lists.linux.dev" <iommu@lists.linux.dev>, "joro@8bytes.org"
	<joro@8bytes.org>
CC: "thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
	"vasant.hegde@amd.com" <vasant.hegde@amd.com>, "michael.roth@amd.com"
	<michael.roth@amd.com>, "jon.grimm@amd.com" <jon.grimm@amd.com>,
	"rientjes@google.com" <rientjes@google.com>
Subject: RE: [PATCH 0/9] iommu/amd: Add AMD IOMMU emulation support for
 SEV-SNP guest kernel
Thread-Topic: [PATCH 0/9] iommu/amd: Add AMD IOMMU emulation support for
 SEV-SNP guest kernel
Thread-Index: AQHamxKg8G3tDdy39E2idvNw1Py2z7GVp95w
Date: Mon, 13 May 2024 20:05:31 +0000
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References: <20240430152430.4245-1-suravee.suthikulpanit@amd.com>
In-Reply-To: <20240430152430.4245-1-suravee.suthikulpanit@amd.com>
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From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Sent: Tuesday, =
April 30, 2024 8:24 AM
>=20
> 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 mech=
anism is
insufficient to avoid the need for interrupt remapping?  (see function poin=
ter
"msi_ext_dest_id").  I'm unclear on whether it is or not. If it is not suff=
icient, 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 thi=
s to be
the more specific "SEV-SNP", and exclude SEV and SEV-ES. For avoid any conf=
usion,
I'd suggest using "SEV-SNP" throughout if that's what you mean.

Michael

>=20
> 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.
>=20
> Testing:
>   - Booting Linux SEV guest w/ 512 vcpus w/ QEMU emulated amd-iommu with
>     qemu-system-x86_64 option: -device amd-iommu,intremap=3Don,xtsup=3Don
>     (emulated devices only for now).
>=20
> GIT repos:
> * https://github.com/AMDESE/linux-iommu/tree/iommu_next_sev-iommu-v1
>=20
> Thanks,
> Suravee
>=20
> 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
>=20
>  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(-)
>=20
> --
> 2.34.1
>=20