linux-kernel - Re: [PATCH 11/12] KVM: MMU: remove kvm_mmu_calc_root_page

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Date:   Fri, 11 Feb 2022 17:53:34 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        vkuznets@...hat.com, mlevitsk@...hat.com, dmatlack@...gle.com
Subject: Re: [PATCH 11/12] KVM: MMU: remove kvm_mmu_calc_root_page_role

IMO, the shortlog is too literal and doesn't help understand the implications of
the change.  I prefer something like:

  KVM: x86/mmu: Always use current mmu's role when loading new PGD

On Wed, Feb 09, 2022, Paolo Bonzini wrote:
> Since the guest PGD is now loaded after the MMU has been set up
> completely, the desired role for a cache hit is simply the current
> mmu_role.  There is no need to compute it again, so __kvm_mmu_new_pgd
> can be folded in kvm_mmu_new_pgd.
> 
> For the !tdp_enabled case, it would also have been possible to use
> the role that is already in vcpu->arch.mmu.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---

With a different shortlog and newline,

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

>  arch/x86/kvm/mmu/mmu.c | 29 ++++-------------------------
>  1 file changed, 4 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index df9e0a43513c..38b40ddcaad7 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -190,8 +190,6 @@ struct kmem_cache *mmu_page_header_cache;
>  static struct percpu_counter kvm_total_used_mmu_pages;
>  
>  static void mmu_spte_set(u64 *sptep, u64 spte);
> -static union kvm_mmu_page_role
> -kvm_mmu_calc_root_page_role(struct kvm_vcpu *vcpu);
>  
>  struct kvm_mmu_role_regs {
>  	const unsigned long cr0;
> @@ -4172,9 +4170,9 @@ static bool fast_pgd_switch(struct kvm_vcpu *vcpu, gpa_t new_pgd,
>  		return cached_root_find_and_replace(vcpu, new_pgd, new_role);
>  }
>  
> -static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd,
> -			      union kvm_mmu_page_role new_role)
> +void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd)
>  {
> +	union kvm_mmu_page_role new_role = vcpu->arch.mmu->mmu_role.base;

Newline needed.

>  	if (!fast_pgd_switch(vcpu, new_pgd, new_role)) {
>  		/* kvm_mmu_ensure_valid_pgd will set up a new root.  */
>  		return;