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SubjectRe: [PATCH v2 5/7] x86/mm, tracing: Fix CR2 corruption
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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