Date: Wed, 5 May 2021 13:56:16 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Vlastimil Babka <vbabka@...e.cz> Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>, dave.hansen@...el.com, luto@...nel.org, linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org, linux-hardening@...r.kernel.org, kernel-hardening@...ts.openwall.com, ira.weiny@...el.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 Wed, May 05, 2021 at 01:08:35PM +0200, Vlastimil Babka wrote: > On 5/5/21 2:30 AM, Rick Edgecombe wrote: > > Why use PKS for this? > > ===================== > > PKS is an upcoming CPU feature that allows supervisor virtual memory > > permissions to be changed without flushing the TLB, like PKU does for user > > memory. Protecting page tables would normally be really expensive because you > > would have to do it with paging itself. PKS helps by providing a way to toggle > > the writability of the page tables with just a per-cpu MSR. > > I can see in patch 8/9 that you are flipping the MSR around individual > operations on page table entries. In my patch I hooked making the page table > writable to obtaining the page table lock (IIRC I had only the PTE level fully > handled though). Wonder if that would be better tradeoff even for your MSR approach? There's also the HIGHPTE code we could abuse to kmap an alias while we're at it.
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