linux-kernel - Re: [PATCH v2 5/8] KVM: x86: Reduce the number of emulator GPRs to '8' for 32-bit KVM

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Date:   Tue, 31 May 2022 11:04:17 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Robert Dinse <nanook@...imo.com>
Subject: Re: [PATCH v2 5/8] KVM: x86: Reduce the number of emulator GPRs to
 '8' for 32-bit KVM

On Thu, May 26, 2022 at 09:08:14PM +0000, Sean Christopherson wrote:
> Reduce the number of GPRs emulated by 32-bit KVM from 16 to 8.  KVM does
> not support emulating 64-bit mode on 32-bit host kernels, and so should
> never generate accesses to R8-15.
> 
> Opportunistically use NR_EMULATOR_GPRS in rsm_load_state_{32,64}() now
> that it is precise and accurate for both flavors.
> 
> Wrap the definition with full #ifdef ugliness; sadly, IS_ENABLED()
> doesn't guarantee a compile-time constant as far as BUILD_BUG_ON() is
> concerned.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook