From: Michael Ellerman <patch-notifications@ellerman•id.au>
To: Paul Mackerras <paulus@ozlabs•org>, linuxppc-dev@ozlabs•org
Cc: "Shreyas B. Prabhu" <shreyas@linux•vnet.ibm.com>
Subject: Re: [1/2] powerpc/64: Re-fix race condition between going idle and entering guest
Date: Wed, 26 Oct 2016 21:21:06 +1100 (AEDT) [thread overview]
Message-ID: <3t3mJL3D45z9sf9@ozlabs.org> (raw)
In-Reply-To: <20161021090305.GA3809@fergus.ozlabs.ibm.com>
On Fri, 2016-21-10 at 09:03:05 UTC, Paul Mackerras wrote:
> Commit 8117ac6a6c2f ("powerpc/powernv: Switch off MMU before entering
> nap/sleep/rvwinkle mode", 2014-12-10) fixed a race condition where one
> thread entering a KVM guest could switch the MMU context to the guest
> while another thread was still in host kernel context with the MMU on.
> That commit moved the point where a thread entering a power-saving
> mode set its kvm_hstate.hwthread_state field in its PACA to
> KVM_HWTHREAD_IN_IDLE from a point where the MMU was on to after the
> MMU had been switched off. That commit also added a comment
> explaining that we have to switch to real mode before setting
> hwthread_state to avoid this race.
>
> Nevertheless, commit 4eae2c9ae54a ("powerpc/powernv: Make
> pnv_powersave_common more generic", 2016-07-08) subsequently moved
> the setting of hwthread_state back to a point where the MMU is on,
> thus reintroducing the race, despite the comment saying that this
> should not be done being included in full in the context lines of
> the patch that did it.
>
> This fixes the race again and adds a bigger and shoutier comment
> explaining the potential race condition.
>
> Cc: stable@vger•kernel.org # v4.8
> Fixes: 4eae2c9ae54a
> Signed-off-by: Paul Mackerras <paulus@ozlabs•org>
Applied to powerpc fixes, thanks.
https://git.kernel.org/powerpc/c/56c46222af0d09149fadec2a3ce9d4
cheers
prev parent reply other threads:[~2016-10-26 10:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-21 9:03 [PATCH 1/2] powerpc/64: Re-fix race condition between going idle and entering guest Paul Mackerras
2016-10-21 9:04 ` [PATCH 2/2] powerpc/64: Fix race condition in setting lock bit in idle/wakeup code Paul Mackerras
2016-10-25 11:46 ` Gautham R Shenoy
2016-10-26 10:21 ` [2/2] " Michael Ellerman
2016-10-21 12:32 ` [PATCH 1/2] powerpc/64: Re-fix race condition between going idle and entering guest Shreyas B. Prabhu
2016-10-25 10:24 ` Gautham R Shenoy
2016-10-26 10:21 ` Michael Ellerman [this message]
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