linux-kernel - Re: SEV guest regression in 4.18

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Date:   Wed, 22 Aug 2018 08:00:34 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Brijesh Singh <brijesh.singh@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: SEV guest regression in 4.18

On Wed, Aug 22, 2018 at 10:14:17AM +0200, Borislav Petkov wrote:
> Dropping Pavel as it bounces.
> 
> On Tue, Aug 21, 2018 at 11:07:38AM -0500, Brijesh Singh wrote:
> > The tsc_early_init() is called before setup_arch() -> init_mem_mapping.
> 
> Ok, I see it, thanks for explaining.
> 
> So back to your original ideas - I'm wondering whether we should define
> a chunk of memory which the hypervisor and guest can share and thus
> communicate over... Something ala SEV-ES also with strictly defined
> layout and put all those variables there. And then the guest can map
> decrypted.

What about creating a data section specifically for shared memory?
The section would be PMD aligned and sized so that it could be mapped
appropriately without having to fracture the page.  Then define a
macro to easily declare data in the new section, a la __read_mostly.
 
> There might be something similar though, I dunno.
> 
> Maybe Paolo has a better idea...
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
> --