linux-kernel - Re: [PATCH v6 4/4] KVM: nSVM: implement on demand allocation of the nested state

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Message-ID: <20201001002657.GD2988@linux.intel.com>
Date:   Wed, 30 Sep 2020 17:26:57 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH v6 4/4] KVM: nSVM: implement on demand allocation of the
 nested state

On Wed, Sep 30, 2020 at 06:35:40PM +0300, Maxim Levitsky wrote:
> On Mon, 2020-09-28 at 22:15 -0700, Sean Christopherson wrote:
> > Side topic, do we actually need 'initialized'?  Wouldn't checking for a
> > valid nested.msrpm or nested.hsave suffice?
> 
> It a matter of taste - I prefer to have a single variable controlling this,
> rather than two. 
> a WARN_ON(svm->nested.initialized && !svm->nested.msrpm || !svm->nested.hsave))
> would probably be nice to have. IMHO I rather leave this like it is if you
> don't object.

I don't have a strong preference.  I wouldn't bother with the second WARN_ON.
Unless you take action, e.g. bail early, a NULL pointer will likely provide a
stack trace soon enough :-).