linux-kernel - Re: [PATCH v3 02/31] KVM: MMU: Introduce struct kvm_page

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Message-ID: <YVOkcn+PzZOpGRMA@google.com>
Date:   Tue, 28 Sep 2021 23:25:38 +0000
From:   David Matlack <dmatlack@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        seanjc@...gle.com, Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH v3 02/31] KVM: MMU: Introduce struct kvm_page_fault

On Fri, Sep 24, 2021 at 12:31:23PM -0400, Paolo Bonzini wrote:
> Create a single structure for arguments that are passed from
> kvm_mmu_do_page_fault to the page fault handlers.  Later
> the structure will grow to include various output parameters
> that are passed back to the next steps in the page fault
> handling.
> 
> Suggested-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/mmu.h | 34 +++++++++++++++++++++++++++++++---
>  1 file changed, 31 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index e9688a9f7b57..0553ef92946e 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -114,17 +114,45 @@ static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu)
>  					  vcpu->arch.mmu->shadow_root_level);
>  }
>  
> +struct kvm_page_fault {
> +	/* arguments to kvm_mmu_do_page_fault.  */
> +	const gpa_t addr;
> +	const u32 error_code;
> +	const bool prefault;

This is somewhat tangential to your change but... I notice KVM uses
"prefetch" and "prefault" interchangably. If we changed prefault to
prefetch here and in kvm_mmu_do_page_fault then that would make the
naming consistent throughout KVM ("prefetch" for everything).

> +
> +	/* Derived from error_code.  */
> +	const bool exec;
> +	const bool write;
> +	const bool present;
> +	const bool rsvd;
> +	const bool user;
> +
> +	/* Derived from mmu.  */
> +	const bool is_tdp;
> +};
> +
>  int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>  		       bool prefault);
>  
>  static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>  					u32 err, bool prefault)
>  {
> +	struct kvm_page_fault fault = {
> +		.addr = cr2_or_gpa,
> +		.error_code = err,
> +		.exec = err & PFERR_FETCH_MASK,
> +		.write = err & PFERR_WRITE_MASK,
> +		.present = err & PFERR_PRESENT_MASK,
> +		.rsvd = err & PFERR_RSVD_MASK,
> +		.user = err & PFERR_USER_MASK,
> +		.prefault = prefault,
> +		.is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault),
> +	};
>  #ifdef CONFIG_RETPOLINE
> -	if (likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault))
> -		return kvm_tdp_page_fault(vcpu, cr2_or_gpa, err, prefault);
> +	if (fault.is_tdp)
> +		return kvm_tdp_page_fault(vcpu, fault.addr, fault.error_code, fault.prefault);
>  #endif
> -	return vcpu->arch.mmu->page_fault(vcpu, cr2_or_gpa, err, prefault);
> +	return vcpu->arch.mmu->page_fault(vcpu, fault.addr, fault.error_code, fault.prefault);
>  }
>  
>  /*
> -- 
> 2.27.0
> 
>