linux-kernel - Re: [PATCH 05/16] KVM: Add member to struct kvm_gfn

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Date: Fri, 17 May 2024 20:58:39 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "seanjc@...gle.com" <seanjc@...gle.com>
CC: "sagis@...gle.com" <sagis@...gle.com>, "dmatlack@...gle.com"
	<dmatlack@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>, "Aktas,
 Erdem" <erdemaktas@...gle.com>
Subject: Re: [PATCH 05/16] KVM: Add member to struct kvm_gfn_range for target
 alias

On Tue, 2024-05-14 at 17:59 -0700, Rick Edgecombe wrote:
>  
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index c3c922bf077f..f92c8b605b03 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -260,11 +260,19 @@ union kvm_mmu_notifier_arg {
>         unsigned long attributes;
>  };
>  
> +enum kvm_process {
> +       BUGGY_KVM_INVALIDATION          = 0,
> +       KVM_PROCESS_SHARED              = BIT(0),
> +       KVM_PROCESS_PRIVATE             = BIT(1),
> +       KVM_PROCESS_PRIVATE_AND_SHARED  = KVM_PROCESS_SHARED |
> KVM_PROCESS_PRIVATE,
> +};
> +

This enum and kvm_tdp_mmu_root_types are very similar. We could teach the
generic KVM code about invaliding roots instead of just private/shared. Then we
could have a single enum: kvm_tdp_mmu_root_types. This leaks arch details a
little more. But since kvm_process is only used by TDX anyway, the abstraction
seems a little excessive.

I think we should just justify it better in the log. Basically that the benefit
is to hide the detail that private and shared are actually on different roots.
And I guess to hide the existence of the mirrored EPT optimization since the
root is named KVM_MIRROR_ROOTS now. The latter seems more worthwhile.