linux-kernel - Re: [PATCH 08/10] KVM: SEV: define VM types for SEV and SEV-ES

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Message-ID: <bb5b0d82-6bdd-41bd-bc29-42c35698b96f@redhat.com>
Date: Thu, 15 Feb 2024 14:40:32 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Michael Roth <michael.roth@....com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, seanjc@...gle.com,
 aik@....com, isaku.yamahata@...el.com
Subject: Re: [PATCH 08/10] KVM: SEV: define VM types for SEV and SEV-ES

On 2/15/24 02:19, Michael Roth wrote:
>>   #define KVM_X86_DEFAULT_VM	0
>>   #define KVM_X86_SW_PROTECTED_VM	(KVM_X86_DEFAULT_VM | __KVM_X86_PRIVATE_MEM_TYPE)
>> +#define KVM_X86_SEV_VM		8
> Hmm... would it make sense to decouple the VM types and their associated
> capabilities? Only bit 2 is left in the lower range after this, and using any
> bits beyond TDX's bit 4 risks overflowing check_extension ioctl's 32-bit return
> value.

Yes, the idea was to leave 0..7 for vendor independent types (with 0 and 
1 in use), 8..15 for AMD (3 of them being reserved already for 
SEV/SEV-ES/SEV-SNP), 16..23 for Intel.

> Maybe a separate lookup table instead?

The mask was nice because it can be used in relatively hot paths... 
I'll keep them but move the constants away from uapi/ headers.

Paolo