Re: [PATCH 3/5] vhost: support upto 509 memory regions

From: Paolo Bonzini
Date: Fri Jun 19 2015 - 12:44:59 EST

On 19/06/2015 18:33, Michael S. Tsirkin wrote:
> On Fri, Jun 19, 2015 at 06:26:27PM +0200, Paolo Bonzini wrote:
>> On 19/06/2015 18:20, Michael S. Tsirkin wrote:
>>>> We could, but I/O is just an example. It can be I/O, a network ring,
>>>> whatever. We cannot audit all address_space_map uses.
>>> No need to audit them all: defer device_add using an hva range until
>>> address_space_unmap drops using hvas in range drops reference count to
>>> 0.
>> That could be forever. You certainly don't want to lockup the monitor
>> forever just because a device model isn't too friendly to memory hot-unplug.
> We can defer the addition, no need to lockup the monitor.

Patches are welcome.

>> That's why you need to audit them (also, it's perfectly in the device
>> model's right to use address_space_unmap this way: it's the guest that's
>> buggy and leaves a dangling reference to a region before unplugging it).
> Then maybe it's not too bad that the guest will crash because the memory
> was unmapped.

That's a matter of taste. I strongly prefer using 12K extra memory per
VCPU to a guest crash.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
Please read the FAQ at