linux-kernel - Re: [PATCH v3 17/17] KVM: x86/tdp_mmu: Take root types for kvm_tdp_mmu_invalidate_all

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Message-ID: <886ebfebf435d40f4f1eabd79515e6a1ddf50ca6.camel@intel.com>
Date: Tue, 9 Jul 2024 22:52:13 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Zhao, Yan Y" <yan.y.zhao@...el.com>
CC: "Gao, Chao" <chao.gao@...el.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"Huang, Kai" <kai.huang@...el.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Aktas, Erdem"
	<erdemaktas@...gle.com>, "dmatlack@...gle.com" <dmatlack@...gle.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH v3 17/17] KVM: x86/tdp_mmu: Take root types for
 kvm_tdp_mmu_invalidate_all_roots()

On Fri, 2024-07-05 at 09:16 +0800, Yan Zhao wrote:
> To keep the existing direct root behavior the same, I think specifying
> KVM_DIRECT_ROOTS | KVM_INVALID_ROOTS in kvm_tdp_mmu_zap_all() is enough.

Right.

> 
> No need to modify tdp_mmu_root_match() do distinguish between invalid direct
> roots and invalid mirror roots. As long as a root is invalid, guest is no
> longer
> affected by it and KVM will not use it any more. The last remaining operation
> to the invalid root is only zapping.
> 
> Distinguishing between invalid direct roots and invalid mirror roots would
> make the code to zap invalid roots unnecessarily complex, e.g.

I'm not sure that it is more complicated. One requires a big comment to explain,
and the other is self explanatory...

> 
> kvm_tdp_mmu_zap_invalidated_roots() is called both in kvm_mmu_uninit_tdp_mmu()
> and kvm_mmu_zap_all_fast().
> 
> - When called in the former, both invalid direct and invalid mirror roots are
>   required to zap;
> - when called in the latter, only invalid direct roots are required to zap.

It might help to put together a full fixup at this point. We have a couple diffs
in this thread, and I'm not 100% which base patch we are talking about at this
point.