Re: Regression with v5.18-rc1 tag on STM32F7 and STM32H7 based boards

[Greg Ungerer <gerg@linux-m68k.org>]

Hi Geert,

On 21/4/22 00:44, Geert Uytterhoeven wrote:
> On Wed, Apr 20, 2022 at 3:53 PM Greg Ungerer <gerg@linux-m68k.org> wrote:
>> On 16/4/22 10:58, Hugh Dickins wrote:
>>> Just to wrap up this thread: the tentative arch/ patches below did not
>>> go into 5.18-rc2, but 5.18-rc3 will contain
>>> 1bdec44b1eee ("tmpfs: fix regressions from wider use of ZERO_PAGE")
>>> which fixes a further issue, and deletes the line which gave you trouble.
>>>
>>> With arch/h8300 removed from linux-next, and arch/arm losing a page by
>>> the patch below, I don't think it's worth my arguing for those changes.
>>> I'd still prefer arch/m68k to expose its empty_zero_page in ZERO_PAGE(),
>>> or else not allocate it; but I won't be pursuing this further.
>>
>> Thanks for pointing this out. It certainly does look wrong to me for
>> the m68k nommu case. I am not aware of any existing issues caused by
>> this - but there is no good reason not to fix it.
>>
>> So I propose this change. Build and run tested on my m68knommu targets.
>>
>> Regards
>> Greg
>>
>>
>>   From f809fb8fbca9e5e637b8fda380955bd799bb3926 Mon Sep 17 00:00:00 2001
>> From: Greg Ungerer <gerg@linux-m68k.org>
>> Date: Wed, 20 Apr 2022 23:27:47 +1000
>> Subject: [PATCH] m68knommu: set ZERO_PAGE() allocated zeroed page
>>
>> The non-MMU m68k pagetable ZERO_PAGE() macro is being set to the
>> somewhat non-sensical value of "virt_to_page(0)". The zeroth page
>> is not in any way guaranteed to be a page full of "0". So the result
>> is that ZERO_PAGE() will almost certainly contain random values.
>>
>> We already allocate a real "empty_zero_page" in the mm setup code shared
>> between MMU m68k and non-MMU m68k. It is just not hooked up to the
>> ZERO_PAGE() macro for the non-MMU m68k case.
>>
>> Fix ZERO_PAGE() to use the allocated "empty_zero_page" pointer.
>>
>> I am not aware of any specific issues caused by the old code.
>>
>> Link: https://lore.kernel.org/linux-m68k/2a462b23-5b8e-bbf4-ec7d-778434a3b9d7@google.com/T/#t
>> Reported-by: Hugh Dickens <hughd@google.com>
>> Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>
>> ---
>>    arch/m68k/include/asm/pgtable_no.h | 3 ++-
>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/m68k/include/asm/pgtable_no.h b/arch/m68k/include/asm/pgtable_no.h
>> index 87151d67d91e..bce5ca56c388 100644
>> --- a/arch/m68k/include/asm/pgtable_no.h
>> +++ b/arch/m68k/include/asm/pgtable_no.h
>> @@ -42,7 +42,8 @@ extern void paging_init(void);
>>     * ZERO_PAGE is a global shared page that is always zero: used
>>     * for zero-mapped memory areas etc..
>>     */
>> -#define ZERO_PAGE(vaddr)       (virt_to_page(0))
>> +extern void *empty_zero_page;
>> +#define ZERO_PAGE(vaddr)       (virt_to_page(empty_zero_page))
>>
>>    /*
>>     * All 32bit addresses are effectively valid for vmalloc...
> 
> And after that (or combined with this?), this can be factored
> out from arch/m68k/include/asm/pgtable_{mm,no}.h into
> arch/m68k/include/asm/pgtable.h.

I think a new patch to do that work on top of this one would be best.
I will work on that.

Regards
Greg



> 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