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

[Avi Kivity]

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.

> 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.

-- 
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