linux-kernel - Re: [PATCH 0/5] Introduce a quirk to control memslot zap behavior

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Date: Thu, 13 Jun 2024 20:01:07 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "sagis@...gle.com"
	<sagis@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "dmatlack@...gle.com" <dmatlack@...gle.com>,
	"Huang, Kai" <kai.huang@...el.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "Aktas, Erdem" <erdemaktas@...gle.com>
Subject: Re: [PATCH 0/5] Introduce a quirk to control memslot zap behavior

On Thu, 2024-06-13 at 14:06 +0800, Yan Zhao wrote:
>       a) Add a condition for TDX VM type in kvm_arch_flush_shadow_memslot()
>          besides the testing of kvm_check_has_quirk(). It is similar to
>          "all new VM types have the quirk disabled". e.g.
> 
>          static inline bool kvm_memslot_flush_zap_all(struct kvm
> *kvm)                    
>         
> {                                                                             
>    
>               return kvm->arch.vm_type != KVM_X86_TDX_VM
> &&                               
>                      kvm_check_has_quirk(kvm,
> KVM_X86_QUIRK_SLOT_ZAP_ALL);                
>          }
>          
>       b) Init the disabled_quirks based on VM type in kernel, extend
>          disabled_quirk querying/setting interface to enforce the quirk to
>          be disabled for TDX.

I'd prefer to go with option (a) here. Because we don't have any behavior
defined yet for KVM_X86_TDX_VM, we don't really need to "disable a quirk" of it.

Instead we could just define KVM_X86_QUIRK_SLOT_ZAP_ALL to be about the behavior
of the existing vm_types. It would be a few lines of documentation to save
implementing and maintaining a whole interface with special logic for TDX. So to
me it doesn't seem worth it, unless there is some other user for a new more
complex quirk interface.