Hi Ard,

On Thu, Dec 23, 2021 at 3:30 PM Ard Biesheuvel [off-list ref] wrote:

On Tue, 21 Dec 2021 at 22:56, Marek Szyprowski [off-list ref] wrote:

quoted

On 21.12.2021 17:20, Ard Biesheuvel wrote:

quoted

On Tue, 21 Dec 2021 at 14:51, Marek Szyprowski [off-list ref] wrote:

quoted

On 21.12.2021 14:34, Ard Biesheuvel wrote:

quoted

On Tue, 21 Dec 2021 at 12:15, Marek Szyprowski [off-list ref] wrote:

quoted

On 21.12.2021 11:44, Ard Biesheuvel wrote:

quoted

On Tue, 21 Dec 2021 at 11:39, Marek Szyprowski [off-list ref] wrote:

quoted

On 22.11.2021 10:28, Ard Biesheuvel wrote:

quoted

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 <redacted>

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.

quoted

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... :/

Thanks.

As i don't have access to this hardware, I am going to have to rely on
someone who does to debug this further. The only alternative is
marking CONFIG_VMAP_STACK broken on MACH_EXYNOS but that would be
unfortunate.

Wish I had seen this thread before...

I've just bisected a resume after s2ram failure on R-Car Gen2 to the same
commit a1c510d0adc604bb ("ARM: implement support for vmap'ed stacks")
in arm/for-next.

Expected output:

    PM: suspend entry (deep)
    Filesystems sync: 0.000 seconds
    Freezing user space processes ... (elapsed 0.010 seconds) done.
    OOM killer disabled.
    Freezing remaining freezable tasks ... (elapsed 0.009 seconds) done.
    Disabling non-boot CPUs ...

[system suspended, this is also where it hangs on failure]

    Enabling non-boot CPUs ...
    CPU1 is up
    sh-eth ee700000.ethernet eth0: Link is Down
    Micrel KSZ8041RNLI ee700000.ethernet-ffffffff:01: attached PHY
driver (mii_bus:phy_addr=ee700000.ethernet-ffffffff:01, irq=193)
    OOM killer enabled.
    Restarting tasks ... done.
    PM: suspend exit

Both wake-on-LAN and wake-up by gpio-keys fail.
Nothing interesting in the kernel log, cfr. above.

Disabling CONFIG_VMAP_STACK fixes the issue for me.

Just like arch/arm/mach-exynos/ (and others), arch/arm/mach-shmobile/
has several *.S files related to secondary CPU bringup.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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