Messages in this thread | | | Subject | Re: [PATCH 1/1] arm64: fix flush_cache_range | From | "Leizhen (ThunderTown)" <> | Date | Wed, 25 May 2016 09:20:16 +0800 |
| |
On 2016/5/24 21:02, Catalin Marinas wrote: > On Tue, May 24, 2016 at 08:19:05PM +0800, Leizhen (ThunderTown) wrote: >> 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. > > flush_cache_range() is primarily used on VIVT caches before changing the > mapping and should not really be implemented on arm64. I don't recall > why we still have the I-cache invalidation, possibly for the ASID-tagged > VIVT I-cache case, though we should have a specific check for this. > > There are some other cases where flush_cache_range() is called and no > D-cache maintenance is necessary on arm64, so I don't want to penalise > them by implementing flush_cache_range(). > >>> 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 > > The change_protection() shouldn't need to flush the caches in > flush_cache_range(). The change_pte_range() function eventually ends up > calling set_pte_at() which calls __sync_icache_dcache() if the mapping > is executable.
OK, I see. But I'm afraid it entered the "if (pte_present(oldpte))" branch in function change_pte_range. Because the test case called mmap to create pte first, then called pte_modify. I will check it later.
> > Can you be more specific about the kernel version you are using, its > configuration? > I used the latest mainline kernel version, and built with arch/arm64/configs/defconfig, ran on our D02 board. I have attached the testcase, you can simply run: sh test.sh [unhandled content-type:application/octet-stream]#!/bin/bash
i=0 while [ 1 ] do ./mprotect04 if [ $? -ne 0 ]; then echo "i=$i, failed" exit 1 fi
i=$(($i+1))
done
| |