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

["Cédric Le Goater" <clg@kaod.org>]

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. 

C.


>> H_INT_SYNC and H_INT_RESET can not.
>>
>> H_INT_GET_OS_REPORTING_LINE and H_INT_SET_OS_REPORTING_LINE are not
>> implemented.
>>
>> C.
>>
>