[PATCH 2/2] powerpc/mm: Warn if W+X pages found on boot

[Christophe Leroy]

Le 02/05/2019 à 07:51, Russell Currey a écrit :
>>>>> +	if (radix_enabled())
>>>>> +		st.start_address = PAGE_OFFSET;
>>>>> +	else
>>>> +		st.start_address = KERN_VIRT_START;
>>>>
>>>> KERN_VIRT_START doesn't exist on PPC32.
>>>>
>>>> Christophe
>>>>
>>> Thanks a lot for the review!  Applied all your suggestions.  What
>>> should I use on PPC32 instead?
>>
>> Indeed it looks like KERN_VIRT_START is defined as 0 for PPC32 at
>> the
>> top of ptdump.c, which look strange to me.
>>
>> I guess PAGE_OFFSET should be the good value for KERN_VIRT_START on
>> PPC32.
>>
>> Christophe
> 
> git blame says you put it there :) I'll set it to PAGE_OFFSET instead
> of zero.  Cheers
> 

Finally it seems that I was right at first place. KERN_VIRT_START should 
be 0 because in walk_pagetables(), it starts with:

pgd_t *pgd = pgd_offset_k(0UL);

Now that KERN_VIRT_START has changed to 0xc0000000, I get a shift of 
0xc0000000 in the display, ie the kernel pages are displayed starting at 
0x80000000 instead of 0xc0000000 (0x80000000 = 0xc0000000 + 0xc0000000)

Since we only want to display kernel pages, I guess we should use

pgd_t *pgd = pgd_offset_k(KERN_VIRT_START); but then we can't use the 
for () loop as it is.

Does it work properly on PPC64 ? If so, that's surprising.

Christophe