linux-kernel - Re: [PATCH V2 3/10] KVM/MMU: Add last_level in the struct mmu_spte

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Message-ID: <572a6ce3-23f6-7b16-a070-4d4a81ee4335@redhat.com>
Date:   Thu, 14 Feb 2019 17:32:17 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     lantianyu1986@...il.com
Cc:     Lan Tianyu <Tianyu.Lan@...rosoft.com>, christoffer.dall@....com,
        marc.zyngier@....com, linux@...linux.org.uk,
        catalin.marinas@....com, will.deacon@....com, jhogan@...nel.org,
        ralf@...ux-mips.org, paul.burton@...s.com, paulus@...abs.org,
        benh@...nel.crashing.org, mpe@...erman.id.au, rkrcmar@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, kvm@...r.kernel.org,
        michael.h.kelley@...rosoft.com, kys@...rosoft.com,
        vkuznets@...hat.com
Subject: Re: [PATCH V2 3/10] KVM/MMU: Add last_level in the struct
 mmu_spte_page

On 02/02/19 02:38, lantianyu1986@...il.com wrote:
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index ce770b446238..70cafd3f95ab 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2918,6 +2918,9 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>  
>  	if (level > PT_PAGE_TABLE_LEVEL)
>  		spte |= PT_PAGE_SIZE_MASK;
> +
> +	sp->last_level = is_last_spte(spte, level);

Wait, I wasn't thinking straight.  If a struct kvm_mmu_page exists, it
is never the last level.  Page table entries for the last level do not
have a struct kvm_mmu_page.

Therefore you don't need the flag after all.  I suspect your
calculations in patch 2 are off by one, and you actually need

	hlist_for_each_entry(sp, range->flush_list, flush_link) {
		int pages = KVM_PAGES_PER_HPAGE(sp->role.level + 1);
		...
	}

For example, if sp->role.level is 1 then the struct kvm_mmu_page is for
a page containing PTEs and covers an area of 2 MiB.

Thanks,

Paolo

>  	if (tdp_enabled)
>  		spte |= kvm_x86_ops->get_mt_mask(vcpu, gfn,
>  			kvm_is_mmio_pfn(pfn));