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

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Message-ID: <56E7CD25.8070507@redhat.com>
Date:	Tue, 15 Mar 2016 09:51:49 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
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 14/03/2016 20:23, Andy Lutomirski wrote:
> On Tue, Oct 27, 2015 at 10:22 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> 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.
>>
> 
> Once Linus pulls tip:x86/asm, x86 should be ready for this.  Want to try again?

Yup, it's on my todo list. :)

Paolo