linux-kernel - Re: [PATCH v7 5/8] KVM: x86/mmu: Don't pass FOLL_GET to __kvm_follow

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Message-ID: <20230706021016.GC3894444@ls.amr.corp.intel.com>
Date:   Wed, 5 Jul 2023 19:10:16 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     David Stevens <stevensd@...omium.org>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Xu <peterx@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, isaku.yamahata@...il.com
Subject: Re: [PATCH v7 5/8] KVM: x86/mmu: Don't pass FOLL_GET to
 __kvm_follow_pfn

On Tue, Jul 04, 2023 at 04:50:50PM +0900,
David Stevens <stevensd@...omium.org> wrote:

> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index cf2c6426a6fc..46c681dc45e6 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -138,7 +138,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
>  	       const struct kvm_memory_slot *slot,
>  	       unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn,
>  	       u64 old_spte, bool prefetch, bool can_unsync,
> -	       bool host_writable, u64 *new_spte)
> +	       bool host_writable, bool is_refcounted, u64 *new_spte)
>  {
>  	int level = sp->role.level;
>  	u64 spte = SPTE_MMU_PRESENT_MASK;
> @@ -188,6 +188,8 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
>  
>  	if (level > PG_LEVEL_4K)
>  		spte |= PT_PAGE_SIZE_MASK;
> +	else if (is_refcounted)
> +		spte |= SPTE_MMU_PAGE_REFCOUNTED;

Is REFCOUNTED for 4K page only?  What guarantees that large page doesn't have
FOLL_GET? or can we set the bit for large page?


>  
>  	if (shadow_memtype_mask)
>  		spte |= static_call(kvm_x86_get_mt_mask)(vcpu, gfn,

-- 
Isaku Yamahata <isaku.yamahata@...il.com>