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Date: Wed, 15 May 2024 02:02:12 +0700
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Subject: Re: [PATCH 0/9] iommu/amd: Add AMD IOMMU emulation support for
 SEV-SNP guest kernel
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To: Michael Kelley <mhklinux@outlook.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>,
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References: <20240430152430.4245-1-suravee.suthikulpanit@amd.com>
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From: "Suthikulpanit, Suravee" <suravee.suthikulpanit@amd.com>
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On 5/14/2024 3:05 AM, Michael Kelley wrote:
> From: Suravee Suthikulpanit<suravee.suthikulpanit@amd.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.

In case of running a Linux VM w/ QEMU/KVM as hypervisor, the 
qemu-system-x86_64 option kvm-msi-ext-dest-id=on would allow booting the 
VM w/ x2APIC ID > 255. However, for other hypervisor, it might not 
support this feature.

>> 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.

Actually, The CC_ATTR_GUEST_MEM_ENCRYPT attribute is true for all SEV 
guests, so this will enable IOMMU emulation for all SEV guests.

Thanks,
Suravee

> Michael