Date: Wed, 5 May 2021 17:00:13 -0700 From: Ira Weiny <ira.weiny@...el.com> To: Kees Cook <keescook@...omium.org> Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>, dave.hansen@...el.com, luto@...nel.org, peterz@...radead.org, linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org, linux-hardening@...r.kernel.org, kernel-hardening@...ts.openwall.com, rppt@...nel.org, dan.j.williams@...el.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH RFC 0/9] PKS write protected page tables On Tue, May 04, 2021 at 11:25:31PM -0700, Kees Cook wrote: > On Tue, May 04, 2021 at 05:30:23PM -0700, Rick Edgecombe wrote: > > > Performance impacts > > =================== > > Setting direct map permissions on whatever random page gets allocated for a > > page table would result in a lot of kernel range shootdowns and direct map > > large page shattering. So the way the PKS page table memory is created is > > similar to this module page clustering series, where a cache of pages is > > replenished from 2MB pages such that the direct map permissions and associated > > breakage is localized on the direct map. In the PKS page tables case, a PKS > > key is pre-applied to the direct map for pages in the cache. > > > > There would be some costs of memory overhead in order to protect the direct > > map page tables. There would also be some extra kernel range shootdowns to > > replenish the cache on occasion, from setting the PKS key on the direct map of > > the new pages. I don’t have any actual performance data yet. > > What CPU models are expected to have PKS? Supervisor Memory Protection Keys (PKS) is a feature which is found on Intel’s Sapphire Rapids (and later) “Scalable Processor” Server CPUs. It will also be available in future non-server Intel parts. Also qemu has some support as well. https://www.qemu.org/2021/04/30/qemu-6-0-0/ Ira
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