From: Catalin Marinas <catalin.marinas@arm.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
Marc Zyngier <maz@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Qais Yousef <qais.yousef@arm.com>,
Suren Baghdasaryan <surenb@google.com>,
Quentin Perret <qperret@google.com>,
kernel-team@android.com
Subject: Re: [PATCH v2 5/6] arm64: Advertise CPUs capable of running 32-bit applications in sysfs
Date: Tue, 10 Nov 2020 10:57:02 +0000 [thread overview]
Message-ID: <X6px/gsuzIFLTIQ7@trantor> (raw)
In-Reply-To: <X6pfISu1PE5lelNL@kroah.com>
On Tue, Nov 10, 2020 at 10:36:33AM +0100, Greg Kroah-Hartman wrote:
> On Tue, Nov 10, 2020 at 09:28:43AM +0000, Catalin Marinas wrote:
> > On Tue, Nov 10, 2020 at 08:04:26AM +0100, Greg Kroah-Hartman wrote:
> > > On Mon, Nov 09, 2020 at 09:30:21PM +0000, Will Deacon wrote:
> > > > Since 32-bit applications will be killed if they are caught trying to
> > > > execute on a 64-bit-only CPU in a mismatched system, advertise the set
> > > > of 32-bit capable CPUs to userspace in sysfs.
> > > >
> > > > Signed-off-by: Will Deacon <will@kernel.org>
> > > > ---
> > > > .../ABI/testing/sysfs-devices-system-cpu | 9 +++++++++
> > > > arch/arm64/kernel/cpufeature.c | 19 +++++++++++++++++++
> > > > 2 files changed, 28 insertions(+)
> > >
> > > I still think the "kill processes that can not run on this CPU" is crazy
> >
> > I agree it's crazy, though we try to keep the kernel support simple
> > while making it a user-space problem. The alternative is to
> > force-migrate such process to a more capable CPU, potentially against
> > the desired user cpumask. In addition, we'd have to block CPU hot-unplug
> > in case the last 32-bit capable CPU disappears.
>
> You should block CPU hot-unplug for the last 32bit capable CPU, why
> would you not want that if there are any active 32bit processes running?
That's been done in one of the versions submitted to the Android kernel
(which also handles automatic task placement, though by overriding the
user cpumask):
https://android-review.googlesource.com/c/kernel/common/+/1437100/7
I think preventing CPU offlining makes sense only together with forcing
32-bit task placement from the kernel. If we decide to go for the
SIGKILL approach with user-driven affinity, careful CPU offlining should
also be handled by user-space.
--
Catalin
next prev parent reply other threads:[~2020-11-10 10:57 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-09 21:30 [PATCH v2 0/6] An alternative series for asymmetric AArch32 systems Will Deacon
2020-11-09 21:30 ` [PATCH v2 1/6] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2020-11-09 21:30 ` [PATCH v2 2/6] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2020-11-11 19:10 ` Catalin Marinas
2020-11-13 9:36 ` Will Deacon
2020-11-13 10:26 ` Catalin Marinas
2020-11-09 21:30 ` [PATCH v2 3/6] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2020-11-10 9:33 ` Marc Zyngier
2020-11-09 21:30 ` [PATCH v2 4/6] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2020-11-09 21:30 ` [PATCH v2 5/6] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2020-11-10 7:04 ` Greg Kroah-Hartman
2020-11-10 9:28 ` Catalin Marinas
2020-11-10 9:36 ` Greg Kroah-Hartman
2020-11-10 9:53 ` Marc Zyngier
2020-11-10 10:10 ` Greg Kroah-Hartman
2020-11-10 10:46 ` Marc Zyngier
2020-11-10 10:57 ` Catalin Marinas [this message]
2020-11-09 21:30 ` [PATCH v2 6/6] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
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