linux-kernel - Re: [PATCH] KVM: x86: fix overlap between SPTE_MMIO

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Date:   Thu, 23 Jan 2020 13:16:53 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: fix overlap between SPTE_MMIO_MASK and
 generation

On 21/01/20 22:04, Sean Christopherson wrote:
>> Alternatively, BUILD_BUG_ON((MMIO_SPTE_GEN_HIGH_MASK |
>> MMIO_SPTE_GEN_LOW_MASK) & SPTE_(MMIO and/or SPECIAL)_MASK)
> Or add both BUILD_BUG_ONs.

In the end I decided to revert MMIO_SPTE_GEN_HIGH_START to
PT64_SECOND_AVAIL_BITS_SHIFT (it makes sense since we use it for
shadow_acc_track_saved_bits_shift, and whether to use
shadow_acc_track_saved_bits_shift or MMIO_SPTE_GEN_HIGH_START depends on
the SPTE_SPECIAL_MASK bits) and use Ben's suggested BUILD_BUG_ON.

Paolo