Re: [Qemu-devel] [big lock] Discussion about the convention of device's DMA each other after breaking down biglock

[liu ping fan]

On Sun, Sep 30, 2012 at 4:13 PM, Avi Kivity <address@hidden> wrote:
> On 09/29/2012 11:20 AM, liu ping fan wrote:
>>
>> Do we have iommus in qemu now,
>
> We do, but they're hacked into the scsi layer, see hw/sun4m_iommu.c.  I
> don't know if it's a standalone iommu on real hardware or whether it is
> part of the HBA.
>
>> since there are no separate phys_maps
>> for real address and dev's virt address, and I think the iommu is only
>> needed by host, not guest, so need not emulated by qemu.
>
> Eventually we will emulate iommus for x86 too, so we need to consider them.
>
For nested guest?  The address translation is like nested mmu?
>> If no, we
>> can just reject the nested DMA, and the c_p_m_rw() can only be nested
>> once, so if introduce a wrapper for c_p_m_rw(), we can avoid
>> recursive big lock, right?
>
> Don't we need that for other reasons?  If not, we can drop it for now.
>
Yes, there is another reason is about the unplug process as you
suggest, DeviceState::uninit() can call del timer with nested biglock.
 Or as alternative, we del timer when unplug and check the valid of
timer when mmio-dispatch in e1000.

Regards,
pingfan
> --
> error compiling committee.c: too many arguments to function