linux-kernel - Re: [PATCH 03/12] KVM: X86/MMU: Split a part of kvm_unsync_page() as kvm_mmu_page_mark

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Date:   Thu, 14 Jul 2022 22:19:05 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Lai Jiangshan <jiangshan.ljs@...group.com>
Subject: Re: [PATCH 03/12] KVM: X86/MMU: Split a part of kvm_unsync_page() as
 kvm_mmu_page_mark_unsync()

On Sun, Jun 05, 2022, Lai Jiangshan wrote:
> From: Lai Jiangshan <jiangshan.ljs@...group.com>
> 
> Make it as the opposite function of kvm_mmu_page_clear_unsync().
> 
> Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index c20981dfc4fd..cc0207e26f6e 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2529,12 +2529,16 @@ static int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva)
>  	return r;
>  }
>  
> -static void kvm_unsync_page(struct kvm *kvm, struct kvm_mmu_page *sp)
> +static void kvm_mmu_page_mark_unsync(struct kvm *kvm, struct kvm_mmu_page *sp)

The existing code is anything but consistent, but I think I prefer the pattern:

	kvm_mmu_<action>_<target>_<flag>

I.e. kvm_mmu_mark_page_unsync() + kvm_mmu_unmark_page_unsync() to yield:

	kvm_mmu_mark_page_unsync(kvm, sp);
	kvm_mmu_mark_parents_unsync(sp);

so that at least this code will be consistent with itself.

>  {
>  	trace_kvm_mmu_unsync_page(sp);
>  	++kvm->stat.mmu_unsync;
>  	sp->unsync = 1;
> +}
>  
> +static void kvm_unsync_page(struct kvm *kvm, struct kvm_mmu_page *sp)

Rather than keep kvm_unsync_page(), what about just open coding the calls in
mmu_try_to_unsync_pages()?  I can't imagine we'll ever have a second caller.

There won't be a direct pair to kvm_sync_page(), but that's not necessarily a bad
thing since they are really direct opposites anyway.

> +{
> +	kvm_mmu_page_mark_unsync(kvm, sp);
>  	kvm_mmu_mark_parents_unsync(sp);
>  }
>  
> -- 
> 2.19.1.6.gb485710b
>