linux-kernel - Re: [PATCH] sched,kvm: Fix KVM preempt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150703154245.GL25159@twins.programming.kicks-ass.net>
Date:	Fri, 3 Jul 2015 17:42:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Pontus Fuchs <pontus.fuchs@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	gleb@...nel.org
Subject: Re: [PATCH] sched,kvm: Fix KVM preempt_notifier usage

On Fri, Jul 03, 2015 at 05:38:42PM +0200, Paolo Bonzini wrote:
> So basically this.  Can you reply with SoB and maybe Acked-by?

Ah, thanks for doing that!

> ------------- 8< ---------------
> From: Peter Zijlstra <peterz@...radead.org>
> Subject: [PATCH] sched, preempt_notifier: separate notifier registration from static_key inc/dec 
> 
> Commit 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
> had two problems.  First, the preempt-notifier API needs to sleep with the
> addition of the static_key, we do however need to hold off preemption
> while modifying the preempt notifier list, otherwise a preemption could
> observe an inconsistent list state.  KVM correctly registers and
> unregisters preempt notifiers with preemption disabled, so the sleep
> caused dmesg splats.
> 
> Second, KVM registers and unregisters preemption notifiers very often
> (in vcpu_load/vcpu_put).  With a single uniprocessor guest the static key
> would move between 0 and 1 continuously, hitting the slow path on every
> userspace exit.
> 
> To fix this, wrap the static_key inc/dec in a new API, and call it from
> KVM.
> 
> Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
> Reported-by: Pontus Fuchs <pontus.fuchs@...il.com>
> Reported-by: Takashi Iwai <tiwai@...e.de>

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/