linux-kernel - Re: [PATCH v13 19/85] KVM: Introduce kvm_follow_pfn() to eventually replace "gfn_to

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Message-ID: <Zxb/AZVD6wvk28OY@yzhao56-desk.sh.intel.com>
Date: Tue, 22 Oct 2024 09:25:21 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, 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>, "Michael Ellerman" <mpe@...erman.id.au>, Anup Patel
	<anup@...infault.org>, "Paul Walmsley" <paul.walmsley@...ive.com>, 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>,
	<kvm@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<kvmarm@...ts.linux.dev>, <loongarch@...ts.linux.dev>,
	<linux-mips@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<kvm-riscv@...ts.infradead.org>, <linux-riscv@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Alex Bennée
	<alex.bennee@...aro.org>, David Matlack <dmatlack@...gle.com>, David Stevens
	<stevensd@...omium.org>, Andrew Jones <ajones@...tanamicro.com>
Subject: Re: [PATCH v13 19/85] KVM: Introduce kvm_follow_pfn() to eventually
 replace "gfn_to_pfn" APIs

On Mon, Oct 21, 2024 at 11:08:49AM -0700, Sean Christopherson wrote:
> On Mon, Oct 21, 2024, Yan Zhao wrote:
> > On Thu, Oct 10, 2024 at 11:23:21AM -0700, Sean Christopherson wrote:
> > > --- a/virt/kvm/pfncache.c
> > > +++ b/virt/kvm/pfncache.c
> > > @@ -159,6 +159,12 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
> > >  	kvm_pfn_t new_pfn = KVM_PFN_ERR_FAULT;
> > >  	void *new_khva = NULL;
> > >  	unsigned long mmu_seq;
> > > +	struct kvm_follow_pfn kfp = {
> > > +		.slot = gpc->memslot,
> > > +		.gfn = gpa_to_gfn(gpc->gpa),
> > > +		.flags = FOLL_WRITE,
> > > +		.hva = gpc->uhva,
> > > +	};
> > Is .map_writable uninitialized?
> 
> Nope, per C99, "subobjects without explicit initializers are initialized to zero",
> i.e. map_writable is initialized to "false".
Ah, thanks, good to know that!