Re: [Qemu-devel] qemu-kvm: Role of flush_icache_range on PPC

[Alexander Graf]

On 28.09.2011, at 16:23, Jan Kiszka wrote:

> Alex,
> 
> we have this diff in qemu-kvm:
> 
> diff --git a/exec.c b/exec.c
> index c1e045d..f188549 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -3950,6 +3955,11 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, 
> uint8_t *buf,
>                     cpu_physical_memory_set_dirty_flags(
>                         addr1, (0xff & ~CODE_DIRTY_FLAG));
>                 }
> +             /* qemu doesn't execute guest code directly, but kvm does
> +                therefore flush instruction caches */
> +             if (kvm_enabled())
> +                 flush_icache_range((unsigned long)ptr,
> +                                    ((unsigned long)ptr)+l);
>                 qemu_put_ram_ptr(ptr);
>             }
>         } else {
> 
> 
> flush_icache_range() is doing something only on PPC hosts. So do we need
> this upstream?

This makes sure that when device emulation overwrites code that is already 
present in the cache of a CPU, it gets flushed from the icache. I'm fairly sure 
we want that :). But let's ask Ben and David as well.


Alex