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

[Pranith Kumar]

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

Thanks,
--
Pranith