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From: Marek Szyprowski <m.szyprowski@samsung.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Russell King <linux@armlinux.org.uk>,
	Nicolas Pitre <nico@fluxnic.net>, Arnd Bergmann <arnd@arndb.de>,
	Kees Cook <keescook@chromium.org>,
	Keith Packard <keithpac@amazon.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Tony Lindgren <tony@atomide.com>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Linux Samsung SOC <linux-samsung-soc@vger.kernel.org>
Subject: Re: [PATCH v4 7/7] ARM: implement support for vmap'ed stacks
Date: Tue, 21 Dec 2021 22:56:21 +0100	[thread overview]
Message-ID: <f469726d-86fb-cf54-2775-d4658d2f3a5d@samsung.com> (raw)
In-Reply-To: <CAMj1kXHQrqZSE1kHaQyQyK6R58EV3cUyvJFmM1JYifaMemyUhQ@mail.gmail.com>

Hi,

On 21.12.2021 17:20, Ard Biesheuvel wrote:
> On Tue, 21 Dec 2021 at 14:51, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>> On 21.12.2021 14:34, Ard Biesheuvel wrote:
>>> On Tue, 21 Dec 2021 at 12:15, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>>>> On 21.12.2021 11:44, Ard Biesheuvel wrote:
>>>>> On Tue, 21 Dec 2021 at 11:39, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>>>>>> On 22.11.2021 10:28, Ard Biesheuvel wrote:
>>>>>>> Wire up the generic support for managing task stack allocations via vmalloc,
>>>>>>> and implement the entry code that detects whether we faulted because of a
>>>>>>> stack overrun (or future stack overrun caused by pushing the pt_regs array)
>>>>>>>
>>>>>>> While this adds a fair amount of tricky entry asm code, it should be
>>>>>>> noted that it only adds a TST + branch to the svc_entry path. The code
>>>>>>> implementing the non-trivial handling of the overflow stack is emitted
>>>>>>> out-of-line into the .text section.
>>>>>>>
>>>>>>> Since on ARM, we rely on do_translation_fault() to keep PMD level page
>>>>>>> table entries that cover the vmalloc region up to date, we need to
>>>>>>> ensure that we don't hit such a stale PMD entry when accessing the
>>>>>>> stack. So we do a dummy read from the new stack while still running from
>>>>>>> the old one on the context switch path, and bump the vmalloc_seq counter
>>>>>>> when PMD level entries in the vmalloc range are modified, so that the MM
>>>>>>> switch fetches the latest version of the entries.
>>>>>>>
>>>>>>> Note that we need to increase the per-mode stack by 1 word, to gain some
>>>>>>> space to stash a GPR until we know it is safe to touch the stack.
>>>>>>> However, due to the cacheline alignment of the struct, this does not
>>>>>>> actually increase the memory footprint of the struct stack array at all.
>>>>>>>
>>>>>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>>>>>> Tested-by: Keith Packard <keithpac@amazon.com>
>>>>>> This patch landed recently in linux-next 20211220 as commit a1c510d0adc6
>>>>>> ("ARM: implement support for vmap'ed stacks"). Sadly it breaks
>>>>>> suspend/resume operation on all ARM 32bit Exynos SoCs. Probably the
>>>>>> suspend/resume related code must be updated somehow (it partially works
>>>>>> on physical addresses and disabled MMU), but I didn't analyze it yet. If
>>>>>> you have any hints, let me know.
>>>>>>
>>>>> Are there any such systems in KernelCI? We caught a suspend/resume
>>>>> related issue in development, which is why the hunk below was added.
>>>> I think that some Exynos-based Odroids (U3 and XU3) were some time ago
>>>> available in KernelCI, but I don't know if they are still there.
>>>>
>>>>
>>>>> In general, any virt-to-phys translation involving and address on the
>>>>> stack will become problematic.
>>>>>
>>>>> Could you please confirm whether the issue persists with the patch
>>>>> applied but with CONFIG_VMAP_STACK turned off? Just so we know we are
>>>>> looking in the right place?
>>>> I've just checked. After disabling CONFIG_VMAP_STACK suspend/resume
>>>> works fine both on commit a1c510d0adc6 and linux-next 20211220.
>>>>
>>> Thanks. Any other context you can provide beyond 'does not work' ?
>> Well, the board properly suspends, but it doesn't wake then (tested
>> remotely with rtcwake command). So far I cannot provide anything more.
>>
> Thanks. Does the below help? Or otherwise, could you try doubling the
> size of the overflow stack at arch/arm/include/asm/thread_info.h:34?

I've tried both (but not at the same time) on the current linux-next and 
none helped. This must be something else... :/


Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland


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  reply	other threads:[~2021-12-21 21:58 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-22  9:28 [PATCH v4 0/7] ARM: add vmap'ed stack support Ard Biesheuvel
2021-11-22  9:28 ` [PATCH v4 1/7] ARM: memcpy: use frame pointer as unwind anchor Ard Biesheuvel
2021-11-22  9:28 ` [PATCH v4 2/7] ARM: memmove: " Ard Biesheuvel
2021-11-22  9:28 ` [PATCH v4 3/7] ARM: memset: clean up unwind annotations Ard Biesheuvel
2021-11-22  9:28 ` [PATCH v4 4/7] ARM: unwind: disregard unwind info before stack frame is set up Ard Biesheuvel
2021-11-22  9:28 ` [PATCH v4 5/7] ARM: switch_to: clean up Thumb2 code path Ard Biesheuvel
2021-11-22  9:28 ` [PATCH v4 6/7] ARM: entry: rework stack realignment code in svc_entry Ard Biesheuvel
2021-11-22  9:28 ` [PATCH v4 7/7] ARM: implement support for vmap'ed stacks Ard Biesheuvel
     [not found]   ` <CGME20211221103854eucas1p2592e38fcc84c1c3506fce87f1dab6739@eucas1p2.samsung.com>
2021-12-21 10:38     ` Marek Szyprowski
2021-12-21 10:42       ` Krzysztof Kozlowski
2021-12-21 10:46         ` Marek Szyprowski
2021-12-21 10:44       ` Ard Biesheuvel
2021-12-21 11:15         ` Marek Szyprowski
2021-12-21 13:34           ` Ard Biesheuvel
2021-12-21 13:51             ` Marek Szyprowski
2021-12-21 16:20               ` Ard Biesheuvel
2021-12-21 21:56                 ` Marek Szyprowski [this message]
2021-12-23 14:23                   ` Ard Biesheuvel
2021-12-28 14:39                     ` Geert Uytterhoeven
2021-12-28 16:12                       ` Geert Uytterhoeven
2021-12-28 16:27                         ` Ard Biesheuvel
2022-01-05 11:08                       ` Jon Hunter
2022-01-05 11:12                         ` Ard Biesheuvel
2022-01-05 11:33                           ` Jon Hunter
2022-01-05 13:53                             ` Russell King (Oracle)
2022-01-05 16:49                           ` Jon Hunter
2022-01-05 17:02                             ` Ard Biesheuvel

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