Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] KVM: mmu: Fix SPTE encoding of MMIO generation upper half
To:     Sean Christopherson <seanjc@google.com>
Cc:     "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>,
        Joerg Roedel <joro@8bytes.org>,
        Jim Mattson <jmattson@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>, linux-doc@vger.kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <156700708db2a5296c5ed7a8b9ac71f1e9765c85.1607129096.git.maciej.szmigiero@oracle.com>
 <370db207-7216-ae26-0c33-dab61e0fdaab@redhat.com>
 <X8/sWzYUjuEYwCuf@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <5e1dc1cd-b175-86be-b33e-0456ecbd50e8@redhat.com>
Date:   Wed, 9 Dec 2020 10:08:47 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.4.0
MIME-Version: 1.0
In-Reply-To: <X8/sWzYUjuEYwCuf@google.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 08/12/20 22:12, Sean Christopherson wrote:
>> #define MMIO_SPTE_GEN_MASK               GENMASK_ULL(MMIO_SPTE_GEN_LOW_BITS + MMIO_SPTE_GEN_HIGH_BITS - 1, 0)
> What if we leave MMIO_SPTE_GEN_MASK as is, GENMASK_ULL(17, 0), and instead add a
> BUILD_BUG_ON() to assert that it matches the above logic?  It's really easy to
> get lost when reading through the chain of defines, I find the explicit mask
> helps provide an anchor/reference for understand what's going on.  It'll require
> an update if/when PT64_SECOND_AVAIL_BITS_SHIFT, but that's not necessarily a bad
> thing, e.g. the comment above this block will also be stale.

Sounds good.

Paolo