Re: [PATCH 06/12] KVM: X86/MMU: Rename mmu_unsync_walk() to mmu_unsync_walk_and_clear()

From: Sean Christopherson <seanjc@google.com>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Maxim Levitsky <mlevitsk@redhat.com>,
	Lai Jiangshan <jiangshan.ljs@antgroup.com>
Subject: Re: [PATCH 06/12] KVM: X86/MMU: Rename mmu_unsync_walk() to mmu_unsync_walk_and_clear()
Date: Tue, 19 Jul 2022 20:07:59 +0000	[thread overview]
Message-ID: <YtcPHx3TYVJzdiN3@google.com> (raw)
In-Reply-To: <20220605064342.309219-7-jiangshanlai@gmail.com>

On Sun, Jun 05, 2022, Lai Jiangshan wrote:
> From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
> 
> mmu_unsync_walk() and __mmu_unsync_walk() requires the caller to clear
> unsync for the shadow pages in the resulted pvec by synching them or
> zapping them.
> 
> All callers does so.
> 
> Otherwise mmu_unsync_walk() and __mmu_unsync_walk() can't work because
> they always walk from the beginning.
> 
> And mmu_unsync_walk() and __mmu_unsync_walk() directly clear unsync bits
> now, rename it.

What about mmu_gather_unsync_shadow_pages()?  I agree that "walk" isn't a great
name, but IMO that's true regardless of when it updates the unsync bitmap.  And
similar to a previous complaint about "clear" being ambiguous, I don't think it's
realistic that we'll be able to come up with a name the precisely and unambiguously
describes what exactly is being cleared.

Instead, regardless of what name we settle on, add a function comment.  Probably
in the patch that changes the clear_unsync_child_bit behavior.  That's a better
place to document the implementation detail.

> Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 2446ede0b7b9..a56d328365e4 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1773,7 +1773,7 @@ static inline void clear_unsync_child_bit(struct kvm_mmu_page *sp, int idx)
>  	__clear_bit(idx, sp->unsync_child_bitmap);
>  }
>  
> -static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
> +static int __mmu_unsync_walk_and_clear(struct kvm_mmu_page *sp,
>  			   struct kvm_mmu_pages *pvec)
>  {
>  	int i, ret, nr_unsync_leaf = 0;
> @@ -1793,7 +1793,7 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
>  			if (mmu_pages_add(pvec, child, i))
>  				return -ENOSPC;
>  
> -			ret = __mmu_unsync_walk(child, pvec);
> +			ret = __mmu_unsync_walk_and_clear(child, pvec);
>  			if (ret < 0)
>  				return ret;
>  			nr_unsync_leaf += ret;
> @@ -1818,7 +1818,7 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
>  
>  #define INVALID_INDEX (-1)
>  
> -static int mmu_unsync_walk(struct kvm_mmu_page *sp,
> +static int mmu_unsync_walk_and_clear(struct kvm_mmu_page *sp,
>  			   struct kvm_mmu_pages *pvec)

Please align indentation.

>  {
>  	pvec->nr = 0;
> @@ -1826,7 +1826,7 @@ static int mmu_unsync_walk(struct kvm_mmu_page *sp,
>  		return 0;
>  
>  	mmu_pages_add(pvec, sp, INVALID_INDEX);
> -	return __mmu_unsync_walk(sp, pvec);
> +	return __mmu_unsync_walk_and_clear(sp, pvec);
>  }
>  
>  static void kvm_mmu_page_clear_unsync(struct kvm *kvm, struct kvm_mmu_page *sp)
> @@ -1962,7 +1962,7 @@ static int mmu_sync_children(struct kvm_vcpu *vcpu,
>  	LIST_HEAD(invalid_list);
>  	bool flush = false;
>  
> -	while (mmu_unsync_walk(parent, &pages)) {
> +	while (mmu_unsync_walk_and_clear(parent, &pages)) {
>  		bool protected = false;
>  
>  		for_each_sp(pages, sp, parents, i)
> @@ -2279,7 +2279,7 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
>  	if (parent->role.level == PG_LEVEL_4K)
>  		return 0;
>  
> -	while (mmu_unsync_walk(parent, &pages)) {
> +	while (mmu_unsync_walk_and_clear(parent, &pages)) {
>  		struct kvm_mmu_page *sp;
>  
>  		for_each_sp(pages, sp, parents, i) {
> -- 
> 2.19.1.6.gb485710b
> 