linux-kernel - Re: [PATCH v2 1/4] KVM: x86/mmu: Track TDP MMU NX huge pages separately

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Message-ID: <20240903202646.GA423248.vipinsh@google.com>
Date: Tue, 3 Sep 2024 13:26:46 -0700
From: Vipin Sharma <vipinsh@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: pbonzini@...hat.com, dmatlack@...gle.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] KVM: x86/mmu: Track TDP MMU NX huge pages
 separately

On 2024-08-29 13:18:27, Sean Christopherson wrote:
> On Thu, Aug 29, 2024, Vipin Sharma wrote:
> > @@ -871,8 +871,17 @@ void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp)
> >  		return;
> >  
> >  	++kvm->stat.nx_lpage_splits;
> > -	list_add_tail(&sp->possible_nx_huge_page_link,
> > -		      &kvm->arch.possible_nx_huge_pages);
> > +	if (is_tdp_mmu_page(sp)) {
> > +#ifdef CONFIG_X86_64
> > +		++kvm->arch.tdp_mmu_possible_nx_huge_pages_count;
> > +		list_add_tail(&sp->possible_nx_huge_page_link,
> > +			      &kvm->arch.tdp_mmu_possible_nx_huge_pages);
> > +#endif
> 
> Pass in the count+list, that way there's no #ifdef and no weird questions for
> what happens if the impossible happens (is_tdp_mmu_page() on 32-bit KVM).
> 
> void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
> 				 u64 *nr_pages, struct list_head *pages)
> {
> 	/*
> 	 * If it's possible to replace the shadow page with an NX huge page,
> 	 * i.e. if the shadow page is the only thing currently preventing KVM
> 	 * from using a huge page, add the shadow page to the list of "to be
> 	 * zapped for NX recovery" pages.  Note, the shadow page can already be
> 	 * on the list if KVM is reusing an existing shadow page, i.e. if KVM
> 	 * links a shadow page at multiple points.
> 	 */
> 	if (!list_empty(&sp->possible_nx_huge_page_link))
> 		return;
> 
> 	++kvm->stat.nx_lpage_splits;
> 	++(*nr_pages);
> 	list_add_tail(&sp->possible_nx_huge_page_link, pages);
> }
> 
Sounds good, I was not sure if passing pointers and incrementing count
via pointer will be accepted.