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From: Marc Zyngier <maz@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: Quentin Perret <qperret@google.com>,
	linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Qais Yousef <qais.yousef@arm.com>,
	Suren Baghdasaryan <surenb@google.com>, Tejun Heo <tj@kernel.org>,
	Li Zefan <lizefan@huawei.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	kernel-team@android.com
Subject: Re: [PATCH v4 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched EL0 support
Date: Wed, 02 Dec 2020 08:18:03 +0000	[thread overview]
Message-ID: <5e59a8f5bc84403ce2c8f26aa874cb1b@kernel.org> (raw)
In-Reply-To: <20201201165707.GF27783@willie-the-truck>

On 2020-12-01 16:57, Will Deacon wrote:
> On Fri, Nov 27, 2020 at 06:16:35PM +0000, Marc Zyngier wrote:
>> On 2020-11-27 17:24, Quentin Perret wrote:
>> > On Friday 27 Nov 2020 at 17:14:11 (+0000), Marc Zyngier wrote:
>> 
>> [...]
>> 
>> > > Yeah, the sanitized read feels better, if only because that is
>> > > what we are going to read in all the valid cases, unfortunately.
>> > > read_sanitised_ftr_reg() is sadly not designed to be called on
>> > > a fast path, meaning that 32bit guests will do a bsearch() on
>> > > the ID-regs every time they exit...
>> > >
>> > > I guess we will have to evaluate how much we loose with this.
>> >
>> > Could we use the trick we have for arm64_ftr_reg_ctrel0 to speed this
>> > up?
>> 
>> Maybe. I want to first verify whether this has any measurable impact.
>> Another possibility would be to cache the last 
>> read_sanitised_ftr_reg()
>> access, just to see if that helps. There shouldn't be that many code
>> paths hammering it.
> 
> We don't have huge numbers of ID registers, so the bsearch shouldn't be
> too expensive. However, I'd like to remind myself why we can't index 
> into
> the feature register array directly as we _should_ know all of this 
> stuff
> at compile time, right?

Simply because it's not indexed by ID reg. It's just an ordered 
collection,
similar to the for sys_reg emulation in KVM. You can compute the index
ahead of time, but just not at compile time. At least not with the
way the arm64_ftr_regs array is built.

         M.
-- 
Jazz is not dead. It just smells funny...

  reply	other threads:[~2020-12-02  8:18 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-24 15:50 [PATCH v4 00/14] An alternative series for asymmetric AArch32 systems Will Deacon
2020-11-24 15:50 ` [PATCH v4 01/14] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2020-11-24 15:50 ` [PATCH v4 02/14] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2020-11-27 10:25   ` Marc Zyngier
2020-11-27 11:50     ` Will Deacon
2020-11-27 13:09   ` Qais Yousef
2020-12-01 16:56     ` Will Deacon
2020-12-02 13:16       ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2020-11-27 10:26   ` Marc Zyngier
2020-11-27 11:53     ` Will Deacon
2020-11-27 17:14       ` Marc Zyngier
2020-11-27 17:24         ` Quentin Perret
2020-11-27 18:16           ` Marc Zyngier
2020-12-01 16:57             ` Will Deacon
2020-12-02  8:18               ` Marc Zyngier [this message]
2020-12-02 17:27                 ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 04/14] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2020-11-27 13:12   ` Qais Yousef
2020-12-01 16:56     ` Will Deacon
2020-12-02 13:52       ` Qais Yousef
2020-12-02 17:42         ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 05/14] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2020-11-24 15:50 ` [PATCH v4 06/14] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
2020-11-27 13:17   ` Qais Yousef
2020-12-01 16:56     ` Will Deacon
2020-11-24 15:50 ` [PATCH v4 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity Will Deacon
2020-11-27  9:49   ` Quentin Perret
2020-11-27 13:19   ` Qais Yousef
2020-12-01 16:56     ` Will Deacon
2020-12-02 13:06       ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon
2020-11-27 10:01   ` Quentin Perret
2020-11-27 13:23   ` Qais Yousef
2020-12-01 16:55     ` Will Deacon
2020-12-02 14:07       ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 09/14] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon
2020-11-27 13:32   ` Qais Yousef
2020-11-30 17:05     ` Qais Yousef
2020-11-30 17:36       ` Quentin Perret
2020-12-01 11:58         ` Qais Yousef
2020-12-01 12:37           ` Quentin Perret
2020-12-01 14:11             ` Qais Yousef
2020-12-01 15:56               ` Quentin Perret
2020-12-01 22:30                 ` Will Deacon
2020-12-02 11:34                   ` Qais Yousef
2020-12-02 11:33                 ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 10/14] sched: Introduce arch_task_cpu_possible_mask() to limit fallback rq selection Will Deacon
2020-11-24 15:50 ` [PATCH v4 11/14] sched: Reject CPU affinity changes based on arch_task_cpu_possible_mask() Will Deacon
2020-11-27  9:54   ` Quentin Perret
2020-11-24 15:50 ` [PATCH v4 12/14] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon
2020-11-27 13:41   ` Qais Yousef
2020-12-01 22:13     ` Will Deacon
2020-12-02 12:59       ` Qais Yousef
2020-12-02 17:42         ` Will Deacon
2020-12-02 18:08           ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 13/14] arm64: Implement arch_task_cpu_possible_mask() Will Deacon
2020-11-27 13:41   ` Qais Yousef
2020-11-24 15:50 ` [PATCH v4 14/14] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon
2020-11-27 13:58 ` [PATCH v4 00/14] An alternative series for asymmetric AArch32 systems Qais Yousef
2020-12-05 20:43 ` Pavel Machek

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