linux-kernel - Re: [PATCH 01/14] KVM: x86/mmu: Expand collapsible SPTE zap for TDP MMU to ZONE

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Date:   Thu, 18 Feb 2021 13:36:21 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.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, Ben Gardon <bgardon@...gle.com>,
        Makarand Sonare <makarandsonare@...gle.com>
Subject: Re: [PATCH 01/14] KVM: x86/mmu: Expand collapsible SPTE zap for TDP
 MMU to ZONE_DEVICE pages

On 13/02/21 01:50, Sean Christopherson wrote:
> Zap SPTEs that are backed by ZONE_DEVICE pages when zappings SPTEs to
> rebuild them as huge pages in the TDP MMU.  ZONE_DEVICE huge pages are
> managed differently than "regular" pages and are not compound pages.
> 
> Cc: Ben Gardon <bgardon@...gle.com>
> Fixes: 14881998566d ("kvm: x86/mmu: Support disabling dirty logging for the tdp MMU")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/mmu/tdp_mmu.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 71e100a5670f..3cc332ed099d 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1348,7 +1348,8 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
>   
>   		pfn = spte_to_pfn(iter.old_spte);
>   		if (kvm_is_reserved_pfn(pfn) ||
> -		    !PageTransCompoundMap(pfn_to_page(pfn)))
> +		    (!PageTransCompoundMap(pfn_to_page(pfn)) &&
> +		     !kvm_is_zone_device_pfn(pfn)))
>   			continue;
>   
>   		tdp_mmu_set_spte(kvm, &iter, 0);
> 

I added a note to the commit message that a similar check is found in 
kvm_mmu_zap_collapsible_spte.

Paolo