Re: [PATCH 1/1] arm64: fix flush_cache_range

From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Xinwei Hu <huxinwei@huawei.com>, Zefan Li <lizefan@huawei.com>,
	Hanjun Guo <guohanjun@huawei.com>,
	Tianhong Ding <dingtianhong@huawei.com>
Subject: Re: [PATCH 1/1] arm64: fix flush_cache_range
Date: Tue, 24 May 2016 20:19:05 +0800	[thread overview]
Message-ID: <574446B9.8040105@huawei.com> (raw)
In-Reply-To: <20160524113727.GD25374@leverpostej>


On 2016/5/24 19:37, Mark Rutland wrote:
> On Tue, May 24, 2016 at 07:16:37PM +0800, Zhen Lei wrote:
>> When we ran mprotect04(a test case in LTP) infinitely, it would always
>> failed after a few seconds. The case can be described briefly that: copy
>> a empty function from code area into a new memory area(created by mmap),
>> then call mprotect to change the protection to PROT_EXEC. The syscall
>> sys_mprotect will finally invoke flush_cache_range, but this function
>> currently only invalid icache, the operation of flush dcache is missed.
> 
> In the LTP code I see powerpc-specific D-cache / I-cache synchronisation
> (i.e. d-cache cleaning followed by I-cache invalidation), so there
> appears to be some expectation of userspace maintenance. Hoever, there
> is no such ARM-specific I-cache maintenance.
But I see some other platforms have D-cache maintenance, like: arch/nios2/mm/cacheflush.c
And according to the name of flush_cache_range, it should do this, I judged. Otherwise,
mprotect04 will be failed on more platforms, it's easy to discover. Only PPC have specific
cache synchronization, maybe it meets some hardware limitation. It's impossible a programmer
fixed a common bug on only one platform but leave others unchanged.

> 
> It looks like the test may be missing I-cache maintenance regardless of
> the semantics of mprotect in this case.
> 
> I have not yet devled into flush_cache_range and how it is called.

SYSCALL_DEFINE3(mprotect ---> mprotect_fixup ---> change_protection ---> change_protection_range --> flush_cache_range

> 
> Thanks,
> Mark.
> 
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
>>  arch/arm64/mm/flush.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
>> index dbd12ea..eda4124 100644
>> --- a/arch/arm64/mm/flush.c
>> +++ b/arch/arm64/mm/flush.c
>> @@ -31,7 +31,7 @@ void flush_cache_range(struct vm_area_struct *vma, unsigned long start,
>>  		       unsigned long end)
>>  {
>>  	if (vma->vm_flags & VM_EXEC)
>> -		__flush_icache_all();
>> +		flush_icache_range(start, end);
>>  }
>>
>>  static void sync_icache_aliases(void *kaddr, unsigned long len)
>> --
>> 2.5.0
>>
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
> 
> .
>