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Subject: Re: [PATCH 02/22] kvm: mmu: Introduce tdp_iter
To:     Eric van Tassell <evantass@amd.com>,
        Ben Gardon <bgardon@google.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     Cannon Matthews <cannonmatthews@google.com>,
        Peter Xu <peterx@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Peter Shier <pshier@google.com>,
        Peter Feiner <pfeiner@google.com>,
        Junaid Shahid <junaids@google.com>,
        Jim Mattson <jmattson@google.com>,
        Yulei Zhang <yulei.kernel@gmail.com>,
        Wanpeng Li <kernellwp@gmail.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Xiao Guangrong <xiaoguangrong.eric@gmail.com>
References: <20200925212302.3979661-1-bgardon@google.com>
 <20200925212302.3979661-3-bgardon@google.com>
 <4a74aafe-9613-4bf2-47a1-cad0aad34323@amd.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <2d43d29f-d29c-3dd7-1709-4414f34d27da@redhat.com>
Date:   Thu, 1 Oct 2020 01:34:53 +0200
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On 01/10/20 01:20, Eric van Tassell wrote:
>>
>> +int is_shadow_present_pte(u64 pte)
>>   {
>>       return (pte != 0) && !is_mmio_spte(pte);
> From <Figure 28-1: Formats of EPTP and EPT Paging-Structure Entries" of
> the manual I don't have at my fingertips right now, I believe you should
> only check the low 3 bits(mask = 0x7). Since the upper bits are ignored,
> might that not mean they're not guaranteed to be 0?

No, this a property of the KVM MMU (and how it builds its PTEs) rather
than the hardware present check.

Paolo