linux-kernel - Re: [PATCH 2/2] KVM: x86/mmu: Add helper to consolidate huge page promotion

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Message-ID: <9b3e3cc3-9cd0-1f55-ee19-f33c4cfb7f8a@redhat.com>
Date:   Wed, 6 Nov 2019 18:22:29 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Adam Borowski <kilobyte@...band.pl>,
        David Hildenbrand <david@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 2/2] KVM: x86/mmu: Add helper to consolidate huge page
 promotion

On 06/11/19 18:07, Sean Christopherson wrote:
>  	 */
> -	if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
> -	    !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL &&
> -	    PageTransCompoundMap(pfn_to_page(pfn)) &&
> +	if (level == PT_PAGE_TABLE_LEVEL && kvm_is_hugepage_allowed(pfn) &&
>  	    !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
>  		unsigned long mask;
>  		/*
> @@ -5914,9 +5919,7 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
>  		 * the guest, and the guest page table is using 4K page size
>  		 * mapping if the indirect sp has level = 1.
>  		 */
> -		if (sp->role.direct && !kvm_is_reserved_pfn(pfn) &&
> -		    !kvm_is_zone_device_pfn(pfn) &&
> -		    PageTransCompoundMap(pfn_to_page(pfn))) {
> +		if (sp->role.direct && kvm_is_hugepage_allowed(pfn)) {
>  			pte_list_remove(rmap_head, sptep);

I don't think is_error_noslot_pfn(pfn) makes sense in
kvm_mmu_zap_collapsible_spte, so I'd rather keep it in
transparent_hugepage_adjust.  Actually, it must be is_noslot_pfn only at
this point---error pfns have been sieved earlier in handle_abnormal_pfn,
so perhaps

	if (WARN_ON_ONCE(is_error_pfn(pfn)) || is_noslot_pfn(pfn))
		return;

	if (level == PT_PAGE_TABLE_LEVEL &&
	    kvm_is_hugepage_allowed(pfn) &&
	    !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL))

would be the best option.

Paolo