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Date: Thu, 30 Aug 2018 21:25:03 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Tony Luck <tony.luck@...el.com> Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Peter Anvin <hpa@...or.com>, Borislav Petkov <bp@...en8.de>, linux-edac <linux-edac@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "the arch/x86 maintainers" <x86@...nel.org>, Dan Williams <dan.j.williams@...el.com>, Dave Jiang <dave.jiang@...el.com> Subject: Re: [PATCH] x86/mce: Fix set_mce_nospec() to avoid #GP fault On Thu, Aug 30, 2018 at 6:49 PM Tony Luck <tony.luck@...el.com> wrote: > > 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. You could literally do something like /* Make it canonical in case we flipped the high bit */ addr = (long)(addr<<1)>>1; in the call to clflush and it magically does the right thing. Pretty? No. But with a big comment about what is going on and why it's done, I think it's prettier than your much bigger patch. I dunno. It does strike me as a bit hacky, but I'd rather have a *small* one-liner hack that generates two instructions, than add a complex hack that modifies the page tables three times and has a serializing instruction in it. Both are subtle fixes for a subtle issue, but one seems pretty harmless in comparison. Hmm? But I'll bow to the x86 maintainers. Linus
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