linux-kernel - Re: [PATCH v2 5/8] KVM: x86/mmu: Use separate namespaces for guest PTEs and shadow PTEs

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Date:   Wed, 15 Jun 2022 15:49:50 +0200
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,
        Lai Jiangshan <jiangshan.ljs@...group.com>
Subject: Re: [PATCH v2 5/8] KVM: x86/mmu: Use separate namespaces for guest
 PTEs and shadow PTEs

On 6/15/22 01:33, Sean Christopherson wrote:
> @@ -2027,8 +2013,8 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
>   	role.direct = direct;
>   	role.access = access;
>   	if (role.has_4_byte_gpte) {
> -		quadrant = gaddr >> (PAGE_SHIFT + (PT64_PT_BITS * level));
> -		quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
> +		quadrant = gaddr >> (PAGE_SHIFT + (SPTE_LEVEL_BITS * level));
> +		quadrant &= (1 << ((PT32_LEVEL_BITS - SPTE_LEVEL_BITS) * level)) - 1;
>   		role.quadrant = quadrant;

That's just a fancy 1, though, and this is just

	/*
	 * Isolate the bits of the address that have already been used by the
	 * 8-byte shadow page table structures, but not yet in the 4-byte guest
	 * page tables.  For example, a 4-byte PDE consumes bits 31:22 and an
	 * 8-byte PDE consumes bits 29:21, so bits 31:30 go in the hash
	 * key.  The hash table look up up ensures that each sPTE points to
	 * the page for the correct portion of the guest page table structure.
	 */
	quadrant = gaddr >> (PAGE_SHIFT + (SPTE_LEVEL_BITS * level));
	quadrant &= (1 << level) - 1;

(Not the best comment, understood).

Paolo