Messages in this thread | | | Date | Mon, 18 Sep 2023 09:35:19 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH RESEND] x86/entry: Don't write to CR3 when restoring to kernel CR3 |
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* Brendan Jackman <jackmanb@google.com> wrote:
> From: Lai Jiangshan <laijs@linux.alibaba.com> > > Skip resuming KERNEL pages since it is already KERNEL CR3 > > Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com> > Signed-off-by: Brendan Jackman <jackmanb@google.com> > --- > > While staring at paranoid_exit I was confused about why we had this CR3 > write, avoiding it seems like a free optimisation. The original commit > 21e94459110252 ("x86/mm: Optimize RESTORE_CR3") says "Most NMI/paranoid > exceptions will not in fact change pagetables" but I didn't't understand > what the "most" was referring to. I then discovered this patch on the > mailing list, Andy said[1] that it looks correct so maybe now is the > time to merge it? > > Note there's another patch in [1] as well, the benefit of that one is > not obvious to me though. > > We've tested an equivalent patch in our internal kernel. > > [1] https://lore.kernel.org/lkml/20200526043507.51977-3-laijs@linux.alibaba.com/ > -- >8 -- > arch/x86/entry/calling.h | 13 ++++--------- > 1 file changed, 4 insertions(+), 9 deletions(-)
I concur that this is a good change, but it would be really nice to get an ack from Andy or Thomas as well.
Thanks,
Ingo
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