Re: [Qemu-devel] [PATCH] kvm: First step to push iothread lock out of inner run loop

[Avi Kivity]

On 06/24/2012 05:51 PM, Jan Kiszka wrote:
> On 2012-06-24 16:46, Avi Kivity wrote:
>> On 06/24/2012 05:40 PM, Jan Kiszka wrote:
>>> On 2012-06-24 16:35, Avi Kivity wrote:
>>>> On 06/24/2012 05:08 PM, Jan Kiszka wrote:
>>>>> As a first step, I will post a series later that gets rid of
>>>>> kvm_flush_coalesced_mmio_buffer in the common vmexit path.
>>>>
>>>> If you defer this, I can think of two places that need to flush:
>>>> - anything that accesses those memory areas (such as DMA to the
>>>> framebuffer, or updating the display)
>>>
>>> - anything that accesses related areas (in case of VGA: PIO accesses to
>>> the control ports). I'm providing memory_region_set_flush_coalesced that
>>> allows to flush on non-coalesced region accesses as well. Some PIO
>>> accesses unfortunately still need open-coded
>>> qemu_flush_coalesced_mmio_buffer as they do not use memory regions yet.
>> 
>> Framebuffer access will bypass the MemoryRegionOps callbacks, did you
>> intend to hook those?
> 
> Are there really cases where the framebuffer is accessible both via MMIO
> and RAM-like mappings at the same time? If so, the current flushing on
> vmexit would help either as the direct mappings would not trigger exits.
> Or what do you mean?

I meant accesses by the display code to put the framebuffer in front of
the user's eyes.  Those just access the memory directly.  We could wrap
them with memory_region_get/put_ram_ptr() (as Xen requires anyway) and
have those issue the flush.


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