linux-kernel - Re: [RFC PATCH 16/21] KVM: x86/mmu: Introduce kvm_split_boundary

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Message-ID: <e731cff1fb840aef22f406e620b28414c583f225.camel@intel.com>
Date: Fri, 16 May 2025 22:16:48 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "quic_eberman@...cinc.com" <quic_eberman@...cinc.com>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "Shutemov, Kirill" <kirill.shutemov@...el.com>,
	"Hansen, Dave" <dave.hansen@...el.com>, "david@...hat.com"
	<david@...hat.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>, "tabba@...gle.com" <tabba@...gle.com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>, "michael.roth@....com"
	<michael.roth@....com>, "seanjc@...gle.com" <seanjc@...gle.com>, "Weiny, Ira"
	<ira.weiny@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"ackerleytng@...gle.com" <ackerleytng@...gle.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "vbabka@...e.cz" <vbabka@...e.cz>, "Peng, Chao P"
	<chao.p.peng@...el.com>, "Du, Fan" <fan.du@...el.com>,
	"binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>, "Annapurve, Vishal"
	<vannapurve@...gle.com>, "jroedel@...e.de" <jroedel@...e.de>, "Miao, Jun"
	<jun.miao@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pgonda@...gle.com" <pgonda@...gle.com>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 16/21] KVM: x86/mmu: Introduce
 kvm_split_boundary_leafs() to split boundary leafs

On Fri, 2025-05-16 at 19:44 +0800, Yan Zhao wrote:
> > > What do you think about relying on tdp_mmu_split_huge_pages_root() and
> > > moving
> > > this to an optimization patch at the end?
> > > 
> > > Or what about just two calls to tdp_mmu_split_huge_pages_root() at the
> > > boundaries?
> > Though the two generally look like the same, relying on
> > tdp_mmu_split_huge_pages_root() will create several minor changes scattering
> > in tdp_mmu_split_huge_pages_root().
> > 
> > e.g. update flush after tdp_mmu_iter_cond_resched(), check
> > iter_split_required(), set "iter.yielded = true".
> > 
> > So, it may be hard to review as a initial RFC.
> > 
> > I prefer to do that after Paolo and Sean have taken a look of it :)
> 
> Oh, I might misunderstood your meaning.
> Yes, if necessary, we can provide a separate patch at the end to combine code
> of
> tdp_mmu_split_huge_pages_root() and tdp_mmu_split_boundary_leafs().

Hmm, I'm not sure if they will look at this version or wait until Intel folks
work through it a bit. As for reviewability, the log could simply explain that
tdp_mmu_split_huge_pages_root() is the simple option and an optimization patch
will follow. I think it's helpful to separate optimization from implementation.
It can be confusing what is for which purpose.