Subject: Re: [PATCH 3/3] powerpc/mm: Use VMALLOC_START to validate addr

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 27 Jun 2022 10:19:15 +0530

Christophe Leroy <[email-masked]> writes:

> Le 23/06/2022 à 14:29, Aneesh Kumar K.V a écrit :
>> Instead of high_memory use VMALLOC_START to validate that the address is
>> not in the vmalloc range.
>
> What's the reason for using VMALLOC_START instead ?
> The gap between high_memory and VMALLOC_START should not be seen as 
> valid memory either, should it ?

Yes and that invalid range should be captured by the pfn_valid check.
Commit ffa0b64e3be5 intended to skip the vmalloc range.
Unfortunately, that resulted in kernel crash due to architecture not
updating high_memory after a memory hotplug. That should be fixed by
patch 1 in this series. patch 3 was added merely as a cleanup to
switch from high_memory to a more familiar VMALLOC_START variable.

>
> If the problem is book3s/64, commit ffa0b64e3be5 ("powerpc: Fix 
> virt_addr_valid() for 64-bit Book3E & 32-bit") says that those 
> additional tests are superfluous for boo3s/64. Maybe it's time to drop 
> unnecessary tests for book3s/64 ?

They are not specific book3s/64. IIUC virt_addr_valid will return false
for an addr after memory hotplug on other platforms too. Patch 1
describe those details.

>
>> 
>> Cc: Kefeng Wang <[email-masked]>
>> Cc: Christophe Leroy <[email-masked]>
>> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
>> ---
>>   arch/powerpc/include/asm/page.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
>> index e5f75c70eda8..256cad69e42e 100644
>> --- a/arch/powerpc/include/asm/page.h
>> +++ b/arch/powerpc/include/asm/page.h
>> @@ -134,7 +134,7 @@ static inline bool pfn_valid(unsigned long pfn)
>>   
>>   #define virt_addr_valid(vaddr)	({					\
>>   	unsigned long _addr = (unsigned long)vaddr;			\
>> -	_addr >= PAGE_OFFSET && _addr < (unsigned long)high_memory &&	\
>> +	_addr >= PAGE_OFFSET && _addr < (unsigned long)VMALLOC_START &&	\
>>   	pfn_valid(virt_to_pfn(_addr));					\
>>   })
>>