Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 5 Jul 2019 12:27:49 +0900 | Subject | Re: [PATCH v2 5/7] x86/mm, tracing: Fix CR2 corruption |
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On Fri, Jul 5, 2019 at 12:16 PM Andy Lutomirski <luto@amacapital.net> wrote: > > If nothing else, MOV to CR2 is architecturally serializing, so, unless there’s some fancy unwinding involved, this will be quite slow.
That's why the NMI code does this:
if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) write_cr2(this_cpu_read(nmi_cr2));
so that it normally only does a read. Only if you actually took a page fault will it restore cr2 to the old value (and if you took a page fault the performance issues will be _there_, not in the "restore cr2" part)
Linus
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