[Qemu-devel] Re: [kvm-devel] [PATCH][UPDATE] kvm-userspace: sync icache for morearchitectures

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Zhang, Xiantao wrote:
>Christian Ehrhardt wrote:
<[...]
>> @@ -2600,8 +2601,8 @@ void cpu_physical_memory_rw(target_phys_addr_t
>>                      addr, uint8_t *buf, phys_ram_dirty[addr1 >>
>>                          TARGET_PAGE_BITS] |= (0xff &
>>                  ~CODE_DIRTY_FLAG); }
>> -#ifdef __ia64__
>> -		kvm_sync_icache((unsigned long)ptr, l);
>> +#ifdef USE_KVM
>> +		flush_icache_range((unsigned long)ptr, ((unsigned
> long)ptr)+l);
> 
> Are you sure ia64 implement this function for applications ? I didn't
> find it at my side, so I write it. 
What do you mean with "implement it for applications" ?
Take a look at dyngen.h - it starts with the comment "dyngen helpers" 
and contains a lot of static functions to use them where you need.
I don't see anything obvious that would prevent these functions from
being built and the file has no own include statements which may 
change that. Therefor the include "dyngen.h" in the USE_KVM case
should be enough to have this function available for
cpu_physical_memory_rw in exec.c where we need it.
[...]
> Xiantao

---

Hollis Blanchard wrote:
> A comment to explain why the icache needs flushing only in the KVM case
> would be useful. Other than that I'm fine with it.
> 
> Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
AFAIK Plain qemu does not directly execute guest code on the processor,
so the icache is not an issue for it.
Qemu itself has the flush_icache_range function only as helper for the
dynamic code generation.
But we may now write executable guest code with our intercepted mmio
handling that is directly executed when switching back to the guest
context, therefore we need that invalidation in the kvm case.

For the case that I'm overlooking something in plain qemu, so that it
might need it too I add qemu-devel@nongnu.org for comments from there,
but currently I think to have it in #ifdef USE_KVM is the right way.


P.S. Hollis did you mean you would like to see a comment in the code
where that call takes place?

-- 

Grüsse / regards, 
Christian Ehrhardt

IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
Ehrhardt@linux.vnet.ibm.com
Ehrhardt@de.ibm.com

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