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

From: "Cédric Le Goater" <clg@kaod.org>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
	Paul Mackerras <paulus@samba.org>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 06/19] KVM: PPC: Book3S HV: add a GET_ESB_FD control to the XIVE native device
Date: Tue, 5 Feb 2019 13:55:40 +0100	[thread overview]
Message-ID: <4d565738-a99b-0333-8533-037677358faa@kaod.org> (raw)
In-Reply-To: <20190205052822.GE22661@umbus.fritz.box>

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@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.

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.

I will give it a try.

Thanks,

C. 