linux-kernel - Re: [PATCH v2 8/8] KVM: SVM: Allocate SEV command structures on local stack

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Date:   Wed, 7 Apr 2021 17:05:07 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        John Allen <john.allen@....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-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 8/8] KVM: SVM: Allocate SEV command structures on
 local stack

On Wed, Apr 07, 2021, Borislav Petkov wrote:
> First of all, I'd strongly suggest you trim your emails when you reply -
> that would be much appreciated.
> 
> On Wed, Apr 07, 2021 at 07:24:54AM +0200, Christophe Leroy wrote:
> > > @@ -258,7 +240,7 @@ static int sev_issue_cmd(struct kvm *kvm, int id, void *data, int *error)
> > >   static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
> > >   {
> > >   	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > > -	struct sev_data_launch_start *start;
> > > +	struct sev_data_launch_start start;
> > 
> > struct sev_data_launch_start start = {0, 0, 0, 0, 0, 0, 0};
> 
> I don't know how this is any better than using memset...
> 
> Also, you can do
> 
> 	... start = { };
> 
> which is certainly the only other alternative to memset, AFAIK.
> 
> But whatever you do, you need to look at the resulting asm the compiler
> generates. So let's do that:

I'm ok with Boris' version, I'm not a fan of having to count zeros.  I used
memset() to defer initialization until after the various sanity checks, and
out of habit.