linux-kernel - Re: [PATCH v3 13/25] KVM: TDX: Fold tdx_mem_page_record_premap

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Message-ID: <aQAOdiSUktmAJKsw@google.com>
Date: Mon, 27 Oct 2025 17:29:42 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>, 
	Huacai Chen <chenhuacai@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>, 
	Anup Patel <anup@...infault.org>, Paul Walmsley <pjw@...nel.org>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, 
	Claudio Imbrenda <imbrenda@...ux.ibm.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	"Kirill A. Shutemov" <kas@...nel.org>, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, kvm@...r.kernel.org, loongarch@...ts.linux.dev, 
	linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, 
	kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org, 
	x86@...nel.org, linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Ira Weiny <ira.weiny@...el.com>, Kai Huang <kai.huang@...el.com>, 
	Michael Roth <michael.roth@....com>, Yan Zhao <yan.y.zhao@...el.com>, 
	Vishal Annapurve <vannapurve@...gle.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Ackerley Tng <ackerleytng@...gle.com>
Subject: Re: [PATCH v3 13/25] KVM: TDX: Fold tdx_mem_page_record_premap_cnt()
 into its sole caller

On Mon, Oct 27, 2025, Binbin Wu wrote:
> 
> 
> On 10/25/2025 12:33 AM, Sean Christopherson wrote:
> > On Fri, Oct 24, 2025, Binbin Wu wrote:
> > > 
> > > On 10/17/2025 8:32 AM, Sean Christopherson wrote:
> > > > Fold tdx_mem_page_record_premap_cnt() into tdx_sept_set_private_spte() as
> > > > providing a one-off helper for effectively three lines of code is at best a
> > > > wash, and splitting the code makes the comment for smp_rmb()  _extremely_
> > > > confusing as the comment talks about reading kvm->arch.pre_fault_allowed
> > > > before kvm_tdx->state, but the immediately visible code does the exact
> > > > opposite.
> > > > 
> > > > Opportunistically rewrite the comments to more explicitly explain who is
> > > > checking what, as well as _why_ the ordering matters.
> > > > 
> > > > No functional change intended.
> > > > 
> > > > Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> > > > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > > Reviewed-by: Binbin Wu <binbin.wu@...ux.intel.com>
> > > 
> > > One nit below.
> > > 
> > > [...]
> > > > +	/*
> > > > +	 * If the TD isn't finalized/runnable, then userspace is initializing
> > > > +	 * the VM image via KVM_TDX_INIT_MEM_REGION.  Increment the number of
> > > > +	 * pages that need to be mapped and initialized via TDH.MEM.PAGE.ADD.
> > > > +	 * KVM_TDX_FINALIZE_VM checks the counter to ensure all mapped pages
> > >                                                                     ^
> > >                                                  Nit: Is pre-mapped better?
> > Yeah, updated (and then it gets deleted a few commits later :-) ).
> Oh, right, nr_premapped will be dropped later.
> 
> Since the whole nr_premapped will be dropped, do we still need a cleanup patch
> like patch 12 which will be dropped finally?

We don't strictly "need" the cleanups, but IMO intermediate cleanups are often
worth doing even if they get thrown away, soo that the code is in a (hopefully)
better state when the "big" functional change comes along.  I.e. if code 'X' is
easier to understand than code 'Y', then theoretically/hopefully X=>Z is also
easier to understand than Y=>Z.