[PATCH v4 7/7] ARM: implement support for vmap'ed stacks

[Krzysztof Kozlowski]

On 21/12/2021 11:38, Marek Szyprowski wrote:
> Hi,
> 
> 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 at kernel.org>
>> Tested-by: Keith Packard <keithpac at 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.
> 
> 

Maybe this one would help?
https://lore.kernel.org/lkml/20211218085843.212497-2-cuigaosheng1@huawei.com/


Best regards,
Krzysztof