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Subject: Re: [RFC PATCH 3/3] nSVM: use svm->nested.save to load vmcb12
 registers and avoid TOC/TOU races
To:     Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org
References: <20210903102039.55422-1-eesposit@redhat.com>
 <20210903102039.55422-4-eesposit@redhat.com>
 <21d2bf8c4e3eb3fc5d297fd13300557ec686b625.camel@redhat.com>
From:   Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-ID: <73b5a5bb-48f2-3a08-c76b-a82b5b69c406@redhat.com>
Date:   Tue, 14 Sep 2021 10:20:32 +0200
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On 12/09/2021 12:42, Maxim Levitsky wrote:
>>   
>> -	if (!nested_vmcb_valid_sregs(vcpu, &vmcb12->save) ||
>> +	if (!nested_vmcb_valid_sregs(vcpu, &svm->nested.save) ||
>>   	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl)) {

> If you use a different struct for the copied fields, then it makes
> sense IMHO to drop the 'control' parameter from nested_vmcb_check_controls,
> and just use the svm->nested.save there directly.
> 

Ok, what you say in patch 2 makes sense to me. I can create a new struct 
vmcb_save_area_cached, but I need to keep nested.ctl because 1) it is 
used also elsewhere, and different fields from the one checked here are 
read/set and 2) using another structure (or the same 
vmcb_save_area_cached) in its place would just duplicate the same fields 
of nested.ctl, creating even more confusion and possible inconsistency.

Let me know if you disagree.

Thank you,
Emanuele