Re: [Qemu-devel] [PATCH v5 28/33] cputlb: make tlb_flush_by_mmuidx safe for MTTCG

[Alex Bennée]

Pranith Kumar <address@hidden> writes:

> Hi Alex,
>
> Alex Bennée writes:
>
>> These flushes allow a per-mmuidx granularity to the TLB flushing and are
>> currently only used by the ARM model. As it is possible to hammer the
>> other vCPU threads with flushes (and build up long queues of identical
>> flushes) we extend mechanism used for the global tlb_flush and set a
>> bitmap describing all the pending flushes. The updates are done
>> atomically to avoid corruption of the bitmap but repeating a flush is
>> certainly not a problem.
>>
>> Signed-off-by: Alex Bennée <address@hidden>
>
> <snip>
>
>>
>>  static inline void tlb_flush_entry(CPUTLBEntry *tlb_entry, target_ulong 
>> addr)
>> @@ -233,16 +288,50 @@ void tlb_flush_page(CPUState *cpu, target_ulong addr)
>>      }
>>  }
>>
>> -void tlb_flush_page_by_mmuidx(CPUState *cpu, target_ulong addr, ...)
>> +/* As we are going to hijack the bottom bits of the page address for a
>> + * mmuidx bit mask we need to fail to build if we can't do that
>> + */
>> +QEMU_BUILD_BUG_ON(NB_MMU_MODES > TARGET_PAGE_BITS);
>> +
>
> FYI, this is causing a build error on my system with gcc 6.2.
>
>   CC      aarch64-softmmu/cputlb.o
> In file included from 
> /home/pranith/devops/code/qemu/include/qemu/osdep.h:36:0,
>                  from /home/pranith/devops/code/qemu/cputlb.c:20:
> /home/pranith/devops/code/qemu/include/exec/cpu-all.h:196:26: error: 
> braced-group within expression allowed only inside a function
>  #define TARGET_PAGE_BITS ({ assert(target_page_bits_decided); \
>                           ^
> /home/pranith/devops/code/qemu/include/qemu/compiler.h:89:54: note: in 
> definition of macro ‘QEMU_BUILD_BUG_ON’
>      typedef char glue(qemu_build_bug_on__,__LINE__)[(x)?-1:1] 
> __attribute__((unused));
>                                                       ^
> /home/pranith/devops/code/qemu/cputlb.c:293:34: note: in expansion of macro 
> ‘TARGET_PAGE_BITS’
>  QEMU_BUILD_BUG_ON(NB_MMU_MODES > TARGET_PAGE_BITS);
>                                   ^~~~~~~~~~~~~~~~
> /home/pranith/devops/code/qemu/rules.mak:60: recipe for target 'cputlb.o' 
> failed
> make[1]: *** [cputlb.o] Error 1
> Makefile:202: recipe for target 'subdir-aarch64-softmmu' failed
> make: *** [subdir-aarch64-softmmu] Error 2

Odd. I'll look into it. What was you configure string and host architecture?

>
> Thanks,


--
Alex Bennée