linux-kernel - Re: [PATCH] KVM: mmu: Fix SPTE encoding of MMIO generation upper half

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Date:   Wed, 9 Dec 2020 10:08:47 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>,
        Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: mmu: Fix SPTE encoding of MMIO generation upper half

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