[PATCH 06/19] KVM: PPC: Book3S HV: add a GET_ESB_FD control to the XIVE native device

[Cédric Le Goater]

On 2/6/19 2:23 AM, David Gibson wrote:
> On Tue, Feb 05, 2019 at 01:55:40PM +0100, Cédric Le Goater wrote:
>> On 2/5/19 6:28 AM, David Gibson wrote:
>>> On Mon, Feb 04, 2019 at 12:30:39PM +0100, Cédric Le Goater wrote:
>>>> On 2/4/19 5:45 AM, David Gibson wrote:
>>>>> On Mon, Jan 07, 2019 at 07:43:18PM +0100, Cédric Le Goater wrote:
>>>>>> This will let the guest create a memory mapping to expose the ESB MMIO
>>>>>> regions used to control the interrupt sources, to trigger events, to
>>>>>> EOI or to turn off the sources.
>>>>>>
>>>>>> Signed-off-by: Cédric Le Goater <clg at kaod.org>
>>>>>> ---
>>>>>>  arch/powerpc/include/uapi/asm/kvm.h   |  4 ++
>>>>>>  arch/powerpc/kvm/book3s_xive_native.c | 97 +++++++++++++++++++++++++++
>>>>>>  2 files changed, 101 insertions(+)
>>>>>>
>>>>>> diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
>>>>>> index 8c876c166ef2..6bb61ba141c2 100644
>>>>>> --- a/arch/powerpc/include/uapi/asm/kvm.h
>>>>>> +++ b/arch/powerpc/include/uapi/asm/kvm.h
>>>>>> @@ -675,4 +675,8 @@ struct kvm_ppc_cpu_char {
>>>>>>  #define  KVM_XICS_PRESENTED		(1ULL << 43)
>>>>>>  #define  KVM_XICS_QUEUED		(1ULL << 44)
>>>>>>  
>>>>>> +/* POWER9 XIVE Native Interrupt Controller */
>>>>>> +#define KVM_DEV_XIVE_GRP_CTRL		1
>>>>>> +#define   KVM_DEV_XIVE_GET_ESB_FD	1
>>>>>
>>>>> Introducing a new FD for ESB and TIMA seems overkill.  Can't you get
>>>>> to both with an mmap() directly on the xive device fd?  Using the
>>>>> offset to distinguish which one to map, obviously.
>>>>
>>>> The page offset would define some sort of user API. It seems feasible.
>>>> But I am not sure this would be practical in the future if we need to 
>>>> tune the length.
>>>
>>> Um.. why not?  I mean, yes the XIVE supports rather a lot of
>>> interrupts, but we have 64-bits of offset we can play with - we can
>>> leave room for billions of ESB slots and still have room for billions
>>> of VPs.
>>
>> So the first 4 pages could be the TIMA pages and then would come  
>> the pages for the interrupt ESBs. I think that we can have different 
>> vm_fault handler for each mapping.
> 
> Um.. no, I'm saying you don't need to tightly pack them.  So you could
> have the ESB pages at 0, the TIMA at, say offset 2^60.

Well, we know that the TIMA is 4 pages wide and is "directly" related
with the KVM interrupt device. So being at offset 0 seems a good idea.
While the ESB segment is of a variable size depending on the number
of IRQs and it can come after I think.

>> I wonder how this will work out with pass-through. As Paul said in 
>> a previous email, it would be better to let QEMU request a new 
>> mapping to handle the ESB pages of the device being passed through.
>> I guess this is not a special case, just another offset and length.
> 
> Right, if we need multiple "chunks" of ESB pages we can given them
> each their own terabyte or several.  No need to be stingy with address
> space.

You can not put them anywhere. They should map the same interrupt range
of ESB pages, overlapping with the underlying segment of IPI ESB pages. 

C.