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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