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Date: Fri, 14 Jun 2019 16:21:43 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Andy Lutomirski <luto@...capital.net>
cc: Dave Hansen <dave.hansen@...el.com>, 
    Marius Hillenbrand <mhillenb@...zon.de>, kvm@...r.kernel.org, 
    linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com, 
    linux-mm@...ck.org, Alexander Graf <graf@...zon.de>, 
    David Woodhouse <dwmw@...zon.co.uk>, 
    the arch/x86 maintainers <x86@...nel.org>, 
    Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC 00/10] Process-local memory allocations for hiding KVM
 secrets

On Wed, 12 Jun 2019, Andy Lutomirski wrote:
> > On Jun 12, 2019, at 12:55 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> > 
> >> On 6/12/19 10:08 AM, Marius Hillenbrand wrote:
> >> This patch series proposes to introduce a region for what we call
> >> process-local memory into the kernel's virtual address space. 
> > 
> > It might be fun to cc some x86 folks on this series.  They might have
> > some relevant opinions. ;)
> > 
> > A few high-level questions:
> > 
> > Why go to all this trouble to hide guest state like registers if all the
> > guest data itself is still mapped?
> > 
> > Where's the context-switching code?  Did I just miss it?
> > 
> > We've discussed having per-cpu page tables where a given PGD is only in
> > use from one CPU at a time.  I *think* this scheme still works in such a
> > case, it just adds one more PGD entry that would have to context-switched.
>
> Fair warning: Linus is on record as absolutely hating this idea. He might
> change his mind, but it’s an uphill battle.

Yes I know, but as a benefit we could get rid of all the GSBASE horrors in
the entry code as we could just put the percpu space into the local PGD.

Thanks,

	tglx

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