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Date: Wed, 21 May 2014 22:32:53 +0000 From: "Luck, Tony" <tony.luck@...el.com> To: Andy Lutomirski <luto@...capital.net> CC: Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>, "Thomas Gleixner" <tglx@...utronix.de>, Linus Torvalds <torvalds@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, "Andi Kleen" <andi@...stfloor.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org> Subject: RE: [RFC] x86_64: A real proposal for iret-less return to kernel >> The recovery path has to do more than just send a signal - it needs to walk processes and >> "mm"s to see which have mapped the physical address that the h/w told us has gone bad. > > I still feel like I'm missing something. If we interrupted user space > code, then the context we're in should be identical to the context > we'll get when we're about to return to userspace. True. And this far along in do_machine_check() we have set all the other cpus free, so the are heading back to whatever context we interrupted them in. So we might be able to do all that other stuff inline here ... we interrupted user mode, so we know we don't hold any locks. Other cpus are running, so they can complete what they are doing to release any locks we might need. But it will take a while (to scan all those processes). And we haven't yet cleared MCG_STATUS ... so another machine check before we do that would be fatal (x86 doesn't allow nesting). Even if we moved the work after the clear of MCG_STATUS we'd still be vulnerable to a new machine check on x86_64 because we are sitting on the one & only machine check stack. -Tony
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