Re: [PATCH 15/19] KVM: PPC: Book3S HV: add get/set accessors for the source configuration

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Feb 07, 2019 at 10:13:48AM +0100, Cédric Le Goater wrote:
> On 2/7/19 3:48 AM, David Gibson wrote:
> > On Wed, Feb 06, 2019 at 08:07:36AM +0100, Cédric Le Goater wrote:
> >> On 2/6/19 2:24 AM, David Gibson wrote:
> >>> On Wed, Feb 06, 2019 at 12:23:29PM +1100, David Gibson wrote:
> >>>> On Tue, Feb 05, 2019 at 02:03:11PM +0100, Cédric Le Goater wrote:
> >>>>> On 2/5/19 6:32 AM, David Gibson wrote:
> >>>>>> On Mon, Feb 04, 2019 at 05:07:28PM +0100, Cédric Le Goater wrote:
> >>>>>>> On 2/4/19 6:21 AM, David Gibson wrote:
> >>>>>>>> On Mon, Jan 07, 2019 at 07:43:27PM +0100, Cédric Le Goater wrote:
> >>>>>>>>> Theses are use to capure the XIVE EAS table of the KVM device, the
> >>>>>>>>> configuration of the source targets.
> >>>>>>>>>
> >>>>>>>>> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> >>>>>>>>> ---
> >>>>>>>>>  arch/powerpc/include/uapi/asm/kvm.h   | 11 ++++
> >>>>>>>>>  arch/powerpc/kvm/book3s_xive_native.c | 87 +++++++++++++++++++++++++++
> >>>>>>>>>  2 files changed, 98 insertions(+)
> >>>>>>>>>
> >>>>>>>>> diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
> >>>>>>>>> index 1a8740629acf..faf024f39858 100644
> >>>>>>>>> --- a/arch/powerpc/include/uapi/asm/kvm.h
> >>>>>>>>> +++ b/arch/powerpc/include/uapi/asm/kvm.h
> >>>>>>>>> @@ -683,9 +683,20 @@ struct kvm_ppc_cpu_char {
> >>>>>>>>>  #define   KVM_DEV_XIVE_SAVE_EQ_PAGES	4
> >>>>>>>>>  #define KVM_DEV_XIVE_GRP_SOURCES	2	/* 64-bit source attributes */
> >>>>>>>>>  #define KVM_DEV_XIVE_GRP_SYNC		3	/* 64-bit source attributes */
> >>>>>>>>> +#define KVM_DEV_XIVE_GRP_EAS		4	/* 64-bit eas attributes */
> >>>>>>>>>  
> >>>>>>>>>  /* Layout of 64-bit XIVE source attribute values */
> >>>>>>>>>  #define KVM_XIVE_LEVEL_SENSITIVE	(1ULL << 0)
> >>>>>>>>>  #define KVM_XIVE_LEVEL_ASSERTED		(1ULL << 1)
> >>>>>>>>>  
> >>>>>>>>> +/* Layout of 64-bit eas attribute values */
> >>>>>>>>> +#define KVM_XIVE_EAS_PRIORITY_SHIFT	0
> >>>>>>>>> +#define KVM_XIVE_EAS_PRIORITY_MASK	0x7
> >>>>>>>>> +#define KVM_XIVE_EAS_SERVER_SHIFT	3
> >>>>>>>>> +#define KVM_XIVE_EAS_SERVER_MASK	0xfffffff8ULL
> >>>>>>>>> +#define KVM_XIVE_EAS_MASK_SHIFT		32
> >>>>>>>>> +#define KVM_XIVE_EAS_MASK_MASK		0x100000000ULL
> >>>>>>>>> +#define KVM_XIVE_EAS_EISN_SHIFT		33
> >>>>>>>>> +#define KVM_XIVE_EAS_EISN_MASK		0xfffffffe00000000ULL
> >>>>>>>>> +
> >>>>>>>>>  #endif /* __LINUX_KVM_POWERPC_H */
> >>>>>>>>> diff --git a/arch/powerpc/kvm/book3s_xive_native.c b/arch/powerpc/kvm/book3s_xive_native.c
> >>>>>>>>> index f2de1bcf3b35..0468b605baa7 100644
> >>>>>>>>> --- a/arch/powerpc/kvm/book3s_xive_native.c
> >>>>>>>>> +++ b/arch/powerpc/kvm/book3s_xive_native.c
> >>>>>>>>> @@ -525,6 +525,88 @@ static int kvmppc_xive_native_sync(struct kvmppc_xive *xive, long irq, u64 addr)
> >>>>>>>>>  	return 0;
> >>>>>>>>>  }
> >>>>>>>>>  
> >>>>>>>>> +static int kvmppc_xive_native_set_eas(struct kvmppc_xive *xive, long irq,
> >>>>>>>>> +				      u64 addr)
> >>>>>>>>
> >>>>>>>> I'd prefer to avoid the name "EAS" here.  IIUC these aren't "raw" EAS
> >>>>>>>> values, but rather essentially the "source config" in the terminology
> >>>>>>>> of the PAPR hcalls.  Which, yes, is basically implemented by setting
> >>>>>>>> the EAS, but since it's the PAPR architected state that we need to
> >>>>>>>> preserve across migration, I'd prefer to stick as close as we can to
> >>>>>>>> the PAPR terminology.
> >>>>>>>
> >>>>>>> But we don't have an equivalent name in the PAPR specs for the tuple 
> >>>>>>> (prio, server). We could use the generic 'target' name may be ? even 
> >>>>>>> if this is usually referring to a CPU number.
> >>>>>>
> >>>>>> Um.. what?  That's about terminology for one of the fields in this
> >>>>>> thing, not about the name for the thing itself.
> >>>>>>
> >>>>>>> Or, IVE (Interrupt Vector Entry) ? which makes some sense. 
> >>>>>>> This is was the former name in HW. I think we recycle it for KVM.
> >>>>>>
> >>>>>> That's a terrible idea, which will make a confusing situation even
> >>>>>> more confusing.
> >>>>>
> >>>>> Let's use SOURCE_CONFIG and QUEUE_CONFIG. The KVM ioctls are very 
> >>>>> similar to the hcalls anyhow.
> >>>>
> >>>> Yes, I think that's a good idea.
> >>>
> >>> Actually... AIUI the SET_CONFIG hcalls shouldn't be a fast path.  
> >>
> >> No indeed. I have move them to standard hcalls in the current version.
> >>
> >>> Can
> >>> we simplify things further by removing the hcall implementation from
> >>> the kernel entirely, and have qemu implement them by basically just
> >>> forwarding them to the appropriate SET_CONFIG ioctl()?
> >>
> >> Yes. I think we could. 
> > 
> > Great!
> > 
> >> The hcalls H_INT_SET_SOURCE_CONFIG and H_INT_SET_QUEUE_CONFIG and 
> >> the KVM ioctls to set the EQ and the SOURCE configuration have a 
> >> lot in common. I need to look at how we can plug the KVM ioctl in 
> >> the hcalls under QEMU.
> >>
> >> We will have to convert the returned error to respect the PAPR 
> >> specs or have the ioctls return H_* errors.
> > 
> > I don't think returning H_* values from a kernel call is a good idea.
> > Converting errors is kinda ugly, but I still think it's the better
> > option.  Note that we already have something like this for the HPT
> > resizing hcalls.
> 
> ok.
>  
> >> Let's dig that idea. If we choose that path, QEMU will have an 
> >> up-to-date EAT and so we won't need to synchronize its state anymore 
> >> for migration.
> > 
> > I guess so, though I don't see that as essential.
> > 
> >> H_INT_GET_SOURCE_CONFIG can be implemented in QEMU without any KVM 
> >> ioctl.
> >>
> >> H_INT_GET_QUEUE_INFO could be implemented in QEMU. I need to check 
> >> how we return the address of the END ESB in sPAPR. We haven't paid 
> >> much attention to these pages because they are not used under Linux
> >> and today the address is returned by OPAL. 
> >>
> >> H_INT_GET_QUEUE_CONFIG is a little more problematic because we need
> >> to query into the XIVE HW the EQ index and toggle bit. OPAL support
> >> is required for that. But we could reduce the KVM support to the 
> >> ioctl querying these EQ information.
> > 
> > Right, and we'd need an ioctl() like that for migration anyway, yes?
> 
> Yes. it is the same need.
> 
> >> H_INT_ESB could be entirely done under QEMU.
> > 
> > This one can actually happen on fairly hot paths, so I think doing
> > that in qemu probably isn't a good idea.
> 
> I agree It would nice to have some performance.
> 
> This hcall is used when LSIs are involved, which is not really a common 
> configuration. There are no OPAL calls involved. And we are duplicating 
> code at the KVM level to retrigger the interrupt when the level is still
> asserted.
> 
> I will benchmark the two options before making a choice.

Ok.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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