linux-kernel - Re: [RFC PATCH v3 46/59] KVM: VMX: Move register caching logic to common code

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Date:   Thu, 25 Nov 2021 21:17:47 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>, isaku.yamahata@...el.com,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     isaku.yamahata@...il.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC PATCH v3 46/59] KVM: VMX: Move register caching logic to
 common code

On 11/25/21 21:11, Thomas Gleixner wrote:
>>
>> Use kvm_x86_ops.cache_reg() in ept_update_paging_mode_cr0() rather than
>> trying to expose vt_cache_reg() to vmx.c, even though it means taking a
>> retpoline.  The code runs if and only if EPT is enabled but unrestricted
>> guest.
> This sentence does not parse because it's not a proper sentence.
> 
>> Only one generation of CPU, Nehalem, supports EPT but not
>> unrestricted guest, and disabling unrestricted guest without also
>> disabling EPT is, to put it bluntly, dumb.
> This one is only significantly better and lacks an explanation what this
> means for the dumb case.

Well, it means a retpoline (see paragraph before).  However, I'm not 
sure why it one wouldn't create a vt.h header with all vt_* functions.

Paolo