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From: Keith Packard <keithp@keithp.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Abbott Liu" <liuwenliang@huawei.com>,
	"Alexander Sverdlin" <alexander.sverdlin@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Anshuman Khandual" <anshuman.khandual@arm.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Bjorn Andersson" <bjorn.andersson@linaro.org>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Hartley Sweeten" <hsweeten@visionengravers.com>,
	"Jens Axboe" <axboe@kernel.dk>, "Jian Cai" <jiancai@google.com>,
	"Joe Perches" <joe@perches.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski@canonical.com>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"Manivannan Sadhasivam" <mani@kernel.org>,
	"Marc Zyngier" <maz@kernel.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Miguel Ojeda" <ojeda@kernel.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Nicolas Pitre" <nico@fluxnic.net>,
	"Rob Herring" <robh@kernel.org>,
	"Russell King" <linux@armlinux.org.uk>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Valentin Schneider" <valentin.schneider@arm.com>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Wolfram Sang (Renesas)" <wsa+renesas@sang-engineering.com>,
	"YiFei Zhu" <yifeifz2@illinois.edu>
Subject: Re: [PATCH 2/3] ARM: Move thread_info into task_struct (v7 only)
Date: Tue, 07 Sep 2021 15:17:09 -0700	[thread overview]
Message-ID: <87pmtkav4q.fsf@keithp.com> (raw)
In-Reply-To: <CAMj1kXHA-GiAj2u4vRbEsnJ6O=cxiNOEgPHWHP+71dB-sp9Nww@mail.gmail.com>


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Ard Biesheuvel <ardb@kernel.org> writes:

> That is still a bit tricky, given that you now have to swap out the
> per-CPU offset when you migrate a task, and the generic code is not
> really set up for that.

Yeah, I decided to just leverage as much generic code as possible and
re-purposed the TPIDRPRW register for 'current', leaving the
per_cpu_offset data in memory. That makes the patch series pretty
compact, with a bunch of restructuring changes followed by fairly short
functional changes.

> I had a stab at this myself today (long boring day with no Internet connection).
>
> https://android-kvm.googlesource.com/linux/+log/refs/heads/ardb/arm32-ti-in-task
>
> It resembles your code in some places - I suppose we went on the same
> journey in a sense :-) We'll fix up the credits before this gets
> resubmitted.

This does look great, and preserves the optimization of keeping the
per_cpu_offset value in a register.

With the series I posted, getting the per_cpu_offset value requires
fetching the cpu value from task_struct and then using that to index the
per_cpu_offset arrray. I don't have a good feeling of how important this
optimization is? We could stick the per_cpu_offset value into
thread_info to avoid one fetch?

> Fixing the per-task stack protector plugin on top of these changes
> should be trivial but I need a coffee first.

I haven't even looked at that step yet :-)

-- 
-keith

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WARNING: multiple messages have this Message-ID (diff)
From: Keith Packard <keithp@keithp.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Abbott Liu" <liuwenliang@huawei.com>,
	"Alexander Sverdlin" <alexander.sverdlin@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Anshuman Khandual" <anshuman.khandual@arm.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Bjorn Andersson" <bjorn.andersson@linaro.org>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Hartley Sweeten" <hsweeten@visionengravers.com>,
	"Jens Axboe" <axboe@kernel.dk>, "Jian Cai" <jiancai@google.com>,
	"Joe Perches" <joe@perches.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski@canonical.com>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"Manivannan Sadhasivam" <mani@kernel.org>,
	"Marc Zyngier" <maz@kernel.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Miguel Ojeda" <ojeda@kernel.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Nicolas Pitre" <nico@fluxnic.net>,
	"Rob Herring" <robh@kernel.org>,
	"Russell King" <linux@armlinux.org.uk>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Valentin Schneider" <valentin.schneider@arm.com>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Wolfram Sang (Renesas)" <wsa+renesas@sang-engineering.com>,
	"YiFei Zhu" <yifeifz2@illinois.edu>
Subject: Re: [PATCH 2/3] ARM: Move thread_info into task_struct (v7 only)
Date: Tue, 07 Sep 2021 15:17:09 -0700	[thread overview]
Message-ID: <87pmtkav4q.fsf@keithp.com> (raw)
In-Reply-To: <CAMj1kXHA-GiAj2u4vRbEsnJ6O=cxiNOEgPHWHP+71dB-sp9Nww@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 1446 bytes --]

Ard Biesheuvel <ardb@kernel.org> writes:

> That is still a bit tricky, given that you now have to swap out the
> per-CPU offset when you migrate a task, and the generic code is not
> really set up for that.

Yeah, I decided to just leverage as much generic code as possible and
re-purposed the TPIDRPRW register for 'current', leaving the
per_cpu_offset data in memory. That makes the patch series pretty
compact, with a bunch of restructuring changes followed by fairly short
functional changes.

> I had a stab at this myself today (long boring day with no Internet connection).
>
> https://android-kvm.googlesource.com/linux/+log/refs/heads/ardb/arm32-ti-in-task
>
> It resembles your code in some places - I suppose we went on the same
> journey in a sense :-) We'll fix up the credits before this gets
> resubmitted.

This does look great, and preserves the optimization of keeping the
per_cpu_offset value in a register.

With the series I posted, getting the per_cpu_offset value requires
fetching the cpu value from task_struct and then using that to index the
per_cpu_offset arrray. I don't have a good feeling of how important this
optimization is? We could stick the per_cpu_offset value into
thread_info to avoid one fetch?

> Fixing the per-task stack protector plugin on top of these changes
> should be trivial but I need a coffee first.

I haven't even looked at that step yet :-)

-- 
-keith

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  reply	other threads:[~2021-09-07 22:19 UTC|newest]

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-02 15:54 [PATCH 0/2]: ARM: Enable THREAD_INFO_IN_TASK Keith Packard
2021-09-02 15:54 ` Keith Packard
2021-09-02 15:54 ` [PATCH 1/2] ARM: Add per-cpu variable holding cpu number Keith Packard
2021-09-02 15:54   ` Keith Packard
2021-09-02 15:54 ` [PATCH 2/2] ARM: Move thread_info into task_struct Keith Packard
2021-09-02 15:54   ` Keith Packard
2021-09-02 16:07 ` [PATCH 0/2]: ARM: Enable THREAD_INFO_IN_TASK Kees Cook
2021-09-02 16:07   ` Kees Cook
2021-09-02 16:18   ` Ard Biesheuvel
2021-09-02 16:18     ` Ard Biesheuvel
2021-09-02 17:37     ` Kees Cook
2021-09-02 17:37       ` Kees Cook
2021-09-02 16:54   ` Russell King (Oracle)
2021-09-02 16:54     ` Russell King (Oracle)
2021-09-02 16:53 ` Russell King (Oracle)
2021-09-02 16:53   ` Russell King (Oracle)
2021-09-02 17:35   ` Kees Cook
2021-09-02 17:35     ` Kees Cook
2021-09-02 17:58   ` Keith Packard
2021-09-02 17:58     ` Keith Packard
2021-09-04  6:09 ` [PATCH 0/2] ARM: support THREAD_INFO_IN_TASK (v7 only) (v2) Keith Packard
2021-09-04  6:09   ` Keith Packard
2021-09-04  6:09   ` [PATCH 1/3] ARM: Pass cpu number to secondary_start_kernel Keith Packard
2021-09-04  6:09     ` Keith Packard
2021-09-05 20:25     ` Ard Biesheuvel
2021-09-05 20:25       ` Ard Biesheuvel
2021-09-04  6:09   ` [PATCH 2/3] ARM: Move thread_info into task_struct (v7 only) Keith Packard
2021-09-04  6:09     ` Keith Packard
2021-09-05 20:56     ` Ard Biesheuvel
2021-09-05 20:56       ` Ard Biesheuvel
2021-09-06  6:14       ` Keith Packard
2021-09-06  6:14         ` Keith Packard
2021-09-06  7:49         ` Ard Biesheuvel
2021-09-06  7:49           ` Ard Biesheuvel
2021-09-07 15:24           ` Keith Packard
2021-09-07 15:24             ` Keith Packard
2021-09-07 16:05             ` Ard Biesheuvel
2021-09-07 16:05               ` Ard Biesheuvel
2021-09-07 22:17               ` Keith Packard [this message]
2021-09-07 22:17                 ` Keith Packard
2021-09-06  6:20       ` Keith Packard
2021-09-06  6:20         ` Keith Packard
2021-09-04  6:09   ` [PATCH 3/3] ARM: Add per-cpu variable cpu_number " Keith Packard
2021-09-04  6:09     ` Keith Packard
2021-09-07 22:00   ` [PATCH 0/7] ARM: support THREAD_INFO_IN_TASK (v3) Keith Packard
2021-09-07 22:00     ` Keith Packard
2021-09-07 22:00     ` [PATCH 1/7] ARM: Pass cpu number to secondary_start_kernel Keith Packard
2021-09-07 22:00       ` Keith Packard
2021-09-07 22:00     ` [PATCH 2/7] ARM: Pass task " Keith Packard
2021-09-07 22:00       ` Keith Packard
2021-09-07 22:00     ` [PATCH 3/7] ARM: Use smp_processor_id() in vfp_pm_suspend instead of ti->cpu Keith Packard
2021-09-07 22:00       ` Keith Packard
2021-09-07 22:00     ` [PATCH 4/7] ARM: Use hack from powerpc to get current cpu number Keith Packard
2021-09-07 22:00       ` Keith Packard
2021-09-08  7:45       ` Ard Biesheuvel
2021-09-08  7:45         ` Ard Biesheuvel
2021-09-07 22:00     ` [PATCH 5/7] ARM: Stop using TPIDRPRW to hold per_cpu_offset Keith Packard
2021-09-07 22:00       ` Keith Packard
2021-09-09 13:54       ` Ard Biesheuvel
2021-09-09 13:54         ` Ard Biesheuvel
2021-09-07 22:00     ` [PATCH 6/7] ARM: Use TPIDRPRW for current Keith Packard
2021-09-07 22:00       ` Keith Packard
2021-09-09 13:56       ` Ard Biesheuvel
2021-09-09 13:56         ` Ard Biesheuvel
2021-09-07 22:00     ` [PATCH 7/7] ARM: Move thread_info into task_struct (v7 only) Keith Packard
2021-09-07 22:00       ` Keith Packard
2021-09-08  7:01     ` [PATCH 0/7] ARM: support THREAD_INFO_IN_TASK (v3) Krzysztof Kozlowski
2021-09-08  7:01       ` Krzysztof Kozlowski
2021-09-08  7:47       ` Ard Biesheuvel
2021-09-08  7:47         ` Ard Biesheuvel
2021-09-08  7:50         ` Geert Uytterhoeven
2021-09-08  7:50           ` Geert Uytterhoeven

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