linux-kernel - Re: [PATCH v5 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active

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Date:   Thu, 6 Sep 2018 11:45:03 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Brijesh Singh <brijesh.singh@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v5 5/5] x86/kvm: Avoid dynamic allocation of pvclock data
 when SEV is active

On Thu, Sep 06, 2018 at 08:33:34PM +0200, Borislav Petkov wrote:
> On Thu, Sep 06, 2018 at 08:54:52AM -0700, Sean Christopherson wrote:
> > My thought was that we could simply define a second array for the SEV
> > case to statically allocate for NR_CPUS since __decrypted has a big
> > chunk of memory that would be ununsed anyways[1]. And since the second
> > array is only used for SEV it can be freed if !SEV.
> 
> Lemme see if I get it straight:
> 
> __decrypted:
> 
>  4K
> 
> __decrypted_XXX:
> 
>  ((num_possible_cpus() * 32) / 4K) pages
> 
> __decrypted_end:
> 
> Am I close?

Yep, though because the 4k chunk in __decrypted is @hv_clock_boot 
that's used for cpus 0-127, __decrypted_XXX would effectively be:

   (((num_possible_cpus() * 32) / 4k) - 1) pages