linux-kernel - Re: [PATCH v2 7/9] KVM: x86/mmu: Add try_get_mt_mask to x86

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Message-ID: <YlXTSQ1k+glvT83K@google.com>
Date:   Tue, 12 Apr 2022 19:30:17 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        David Matlack <dmatlack@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Dunn <daviddunn@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Junaid Shahid <junaids@...gle.com>
Subject: Re: [PATCH v2 7/9] KVM: x86/mmu: Add try_get_mt_mask to x86_ops

On Mon, Apr 11, 2022, Sean Christopherson wrote:
> It's obviously not a hard dependency, but using a u64 for the mask here and then
> undoing the whole thing is rather silly.  Compile tested only at this point, I'll
> test on an actual system ASAP and let you know if I did something stupid.
> 
> From: Sean Christopherson <seanjc@...gle.com>
> Date: Mon, 11 Apr 2022 15:12:16 -0700
> Subject: [PATCH] KVM: x86: Restrict get_mt_mask() to a u8, use
>  KVM_X86_OP_OPTIONAL_RET0

Verified this works as expected when patching in RET0 on a 32-bit kernel (returning
a u64 results in reserved bits in the upper half being set due to EDX not being cleared).