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Date: Thu, 14 Dec 2017 13:03:37 +0100 (CET) From: Thomas Gleixner <tglx@...utronix.de> To: Peter Zijlstra <peterz@...radead.org> cc: linux-kernel@...r.kernel.org, x86@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>, Andy Lutomirsky <luto@...nel.org>, Dave Hansen <dave.hansen@...el.com>, Borislav Petkov <bpetkov@...e.de>, Greg KH <gregkh@...uxfoundation.org>, keescook@...gle.com, hughd@...gle.com, Brian Gerst <brgerst@...il.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Denys Vlasenko <dvlasenk@...hat.com>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Juergen Gross <jgross@...e.com>, David Laight <David.Laight@...lab.com>, Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com, Will Deacon <will.deacon@....com>, linux-mm@...ck.org, kirill.shutemov@...ux.intel.com, dan.j.williams@...el.com Subject: Re: [PATCH v2 00/17] x86/ldt: Use a VMA based read only mapping On Thu, 14 Dec 2017, Peter Zijlstra wrote: > So here's a second posting of the VMA based LDT implementation; now without > most of the crazy. > > I took out the write fault handler and the magic LAR touching code. > > Additionally there are a bunch of patches that address generic vm issue. > > - gup() access control; In specific I looked at accessing !_PAGE_USER pages > because these patches rely on not being able to do that. > > - special mappings; A whole bunch of mmap ops don't make sense on special > mappings so disallow them. > > Both things make sense independent of the rest of the series. Similarly, the > patches that kill that rediculous LDT inherit on exec() are also unquestionably > good. > > So I think at least the first 6 patches are good, irrespective of the > VMA approach. > > On the whole VMA approach, Andy I know you hate it with a passion, but I really > rather like how it ties the LDT to the process that it belongs to and it > reduces the amount of 'special' pages in the whole PTI mapping. > > I'm not the one going to make the decision on this; but I figured I at least > post a version without the obvious crap parts of the last one. > > Note: if we were to also disallow munmap() for special mappings (which I > suppose makes perfect sense) then we could further reduce the actual LDT > code (we'd no longer need the sm::close callback and related things). That makes a lot of sense for the other special mapping users like VDSO and kprobes. Thanks, tglx
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