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Date: Thu, 30 Aug 2018 18:48:50 -0700 From: Tony Luck <tony.luck@...el.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>, Linux Edac Mailing List <linux-edac@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, X86-ML <x86@...nel.org>, Dan Williams <dan.j.williams@...el.com>, dave.jiang@...el.com Subject: Re: [PATCH] x86/mce: Fix set_mce_nospec() to avoid #GP fault On Thu, Aug 30, 2018 at 6:30 PM Linus Torvalds <torvalds@...ux-foundation.org> wrote: > > On Thu, Aug 30, 2018 at 2:45 PM Tony Luck <tony.luck@...el.com> wrote: > > > > Fix is to move one step at a time. First mark the page not present > > (using the decoy address). Then it is safe to use the actual address > > of the 1:1 mapping to mark it "uc", and finally as present. > > Can't we do it in one step, but make sure that he clflush gets the real address? > I'd like to, but I'd need to have a way to mark the address as needing fixing as it gets passed from set_memory_uc() to _set_memory_uc() to change_page_attr_set() to change_page_attr_set_clear() Just checking "do we have a non-canonical address" at the bottom of that call stack and flipping bit 63 back on again seems like a bad idea. But adding extra flag arguments is majorly ugly too. -Tony
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