linux-kernel - Re: [PATCH 3/3] x86: context_tracking: avoid irq_save/irq

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Message-ID: <CALCETrV01xm5TPngvU1TZzhx3+Ht7eRrkOV5b3tmgU81f_o5Ug@mail.gmail.com>
Date:	Tue, 27 Oct 2015 22:22:44 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 3/3] x86: context_tracking: avoid irq_save/irq_restore on
 kernel entry and exit

On Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> x86 always calls user_enter and user_exit with interrupt disabled.
> Therefore, it is not necessary to check for exceptions, nor to
> save/restore the IRQ state, when context tracking functions are
> called by guest_enter and guest_exit.
>
> Use the previously introduced __context_tracking_entry and
> __context_tracking_exit.

x86 isn't ready for this yet.  We could do a quick-and-dirty fix with
explicit IRQs-on-and-off much protected by the static key, or we could
just wait until I finish the syscall cleanup.  I favor the latter, but
you're all welcome to do the former and I'll review it.

BTW, Frederic, I have a static key patch coming that I think you'll
like.  I'll send it tomorrow once I'm in front of a real computer.

--Andy
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