linux-kernel - Re: [PATCH 2/2] powerpc: Don't ignore errors from set_memory_{n}p() in __kernel_map

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Date: Thu, 22 Feb 2024 09:59:35 +1100
From: Michael Ellerman <mpe@...erman.id.au>
To: Christophe Leroy <christophe.leroy@...roup.eu>, Nicholas Piggin
 <npiggin@...il.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 2/2] powerpc: Don't ignore errors from set_memory_{n}p()
 in __kernel_map_pages()

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> Le 21/02/2024 à 13:09, Michael Ellerman a écrit :
>> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>> set_memory_p() and set_memory_np() can fail.
>>>
>>> As mentioned in linux/mm.h:
>>>
>>> /*
>>>   * To support DEBUG_PAGEALLOC architecture must ensure that
>>>   * __kernel_map_pages() never fails
>>>   */
>>>
>>> So panic in case set_memory_p() or set_memory_np() fail
>>> in __kernel_map_pages().
>>>
>>> Link: https://github.com/KSPP/linux/issues/7
>>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>>> ---
>>>   arch/powerpc/include/asm/book3s/64/hash.h |  2 +-
>>>   arch/powerpc/mm/book3s64/hash_utils.c     |  3 ++-
>>>   arch/powerpc/mm/pageattr.c                | 10 +++++++---
>>>   3 files changed, 10 insertions(+), 5 deletions(-)
>>>
>> ...
>>> diff --git a/arch/powerpc/mm/pageattr.c b/arch/powerpc/mm/pageattr.c
>>> index 16b8d20d6ca8..62b678585878 100644
>>> --- a/arch/powerpc/mm/pageattr.c
>>> +++ b/arch/powerpc/mm/pageattr.c
>>> @@ -106,17 +106,21 @@ int change_memory_attr(unsigned long addr, int numpages, long action)
>>>   #ifdef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
>>>   void __kernel_map_pages(struct page *page, int numpages, int enable)
>>>   {
>>> +	int err;
>>>   	unsigned long addr = (unsigned long)page_address(page);
>>>   
>>>   	if (PageHighMem(page))
>>>   		return;
>>>   
>>>   	if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && !radix_enabled())
>>> -		hash__kernel_map_pages(page, numpages, enable);
>>> +		err = hash__kernel_map_pages(page, numpages, enable);
>>>   	else if (enable)
>>> -		set_memory_p(addr, numpages);
>>> +		err = set_memory_p(addr, numpages);
>>>   	else
>>> -		set_memory_np(addr, numpages);
>>> +		err = set_memory_np(addr, numpages);
>>> +
>>> +	if (err)
>>> +		panic("%s: set_memory_%sp() failed\n", enable ? "" : "n");
>> 
>> This doesn't compile, it's missing __func__ I guess.
>
> Damn, I was too quick when I took into account checkpatch's feedback, 
> sorry for that.
>
>> 
>> Seems like we could keep it simpler though, it should hopefully never
>> happen anyway, eg:
>> 
>>    panic("%s: changing memory protections failed\n", __func__);
>
> Sure, let's do that. Do you want a v2 or you do the change directly ?

No need for a v2, I'll just fix it up when applying.

cheers