linux-kernel - Re: [PATCH v12 01/24] KVM: x86: Rename kvm_{g,s}et_msr()* to show that they emulate guest accesses

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Message-ID: <aLb_BTmViawQyXbG@google.com>
Date: Tue, 2 Sep 2025 07:28:21 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Chao Gao <chao.gao@...el.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	mlevitsk@...hat.com, rick.p.edgecombe@...el.com, weijiang.yang@...el.com, 
	xin@...or.com, Mathias Krause <minipli@...ecurity.net>, John Allen <john.allen@....com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v12 01/24] KVM: x86: Rename kvm_{g,s}et_msr()* to show
 that they emulate guest accesses

On Mon, Sep 01, 2025, Xiaoyao Li wrote:
> On 8/12/2025 10:55 AM, Chao Gao wrote:
> 
> ...
> 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index f19a76d3ca0e..86e4d0b8469b 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -2149,11 +2149,11 @@ void kvm_prepare_event_vectoring_exit(struct kvm_vcpu *vcpu, gpa_t gpa);
> >   void kvm_enable_efer_bits(u64);
> >   bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);
> > -int kvm_get_msr_with_filter(struct kvm_vcpu *vcpu, u32 index, u64 *data);
> > -int kvm_set_msr_with_filter(struct kvm_vcpu *vcpu, u32 index, u64 data);
> > +int kvm_emulate_msr_read(struct kvm_vcpu *vcpu, u32 index, u64 *data);
> > +int kvm_emulate_msr_write(struct kvm_vcpu *vcpu, u32 index, u64 data);
> ...
> > -int kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data);
> > -int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data);
> > +int __kvm_emulate_msr_read(struct kvm_vcpu *vcpu, u32 index, u64 *data);
> > +int __kvm_emulate_msr_write(struct kvm_vcpu *vcpu, u32 index, u64 data);
> 
> I dislike the rename, it loses the information of filter.
> 
> can we keep the filer information and make them as below?
> 
>   kvm_get_msr_with_filter() -> kvm_emulate_msr_read_with_filter()
>   kvm_get_msr() -> kvm_emulate_msr_read()
>   kvm_set_msr_with_filter() -> kvm_emulate_msr_write_with_filter()
>   kvm_set_msr() -> kvm_emulate_msr_write()

Sorry, no.  I detest the "with_filter".  Requiring developers to add "with_filter"
suggests that emulating an access _with_ the filter is somehow exceptional.  That's
the exact opposite of the truth: emulating MSR accesses _without_ the filter should
only be done in very rare situations, e.g. when loading guest state as part of a
complex transition (RSM, SMI, VM-Enter, VM-Exit).

And if we keep "with_filter", the relationship between kvm_emulate_msr_{read,write}()
and __kvm_emulate_msr_{read,write}() will be non-obvious.