[PATCH 08/19] KVM: PPC: Book3S HV: add a VC_BASE control to the XIVE native device

[Cédric Le Goater]

On 2/4/19 5:49 AM, David Gibson wrote:
> On Wed, Jan 23, 2019 at 05:56:26PM +0100, Cédric Le Goater wrote:
>> On 1/22/19 6:14 AM, Paul Mackerras wrote:
>>> On Mon, Jan 07, 2019 at 07:43:20PM +0100, Cédric Le Goater wrote:
>>>> The ESB MMIO region controls the interrupt sources of the guest. QEMU
>>>> will query an fd (GET_ESB_FD ioctl) and map this region at a specific
>>>> address for the guest to use. The guest will obtain this information
>>>> using the H_INT_GET_SOURCE_INFO hcall. To inform KVM of the address
>>>> setting used by QEMU, add a VC_BASE control to the KVM XIVE device
>>>
>>> This needs a little more explanation.  I *think* the only way this
>>> gets used is that it gets returned to the guest by the new
>>> hypercalls.  If that is indeed the case it would be useful to mention
>>> that in the patch description, because otherwise taking a value that
>>> userspace provides and which looks like it is an address, and not
>>> doing any validation on it, looks a bit scary.
>>
>> I think we have solved this problem in another email thread. 
>>
>> The H_INT_GET_SOURCE_INFO hcall does not need to be implemented in KVM
>> as all the source information should already be available in QEMU. In
>> that case, there is no need to inform KVM of where the ESB pages are 
>> mapped in the guest address space. So we don't need that extra control
>> on the KVM device. This is good news.
> 
> Ah, good to hear.  I thought this looked strange.

yes. I didn't know which path to choose between HV real mode, HV, QEMU. 
It's clarified now. 

But now, we have nested, and this is adding quite a bit of strangeness 
to the hcall possibilities.

C.