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Subject: Re: [PATCH 11/19] KVM: PPC: Book3S HV: add support for the XIVE
 native exploitation mode hcalls
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 Paul Mackerras <paulus@ozlabs.org>
References: <20190107184331.8429-1-clg@kaod.org>
 <20190107184331.8429-12-clg@kaod.org> <20190122052346.GF15124@blackberry>
 <de777e750665d92509b1487a90acb79d70854cf3.camel@kernel.crashing.org>
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Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
 David Gibson <david@gibson.dropbear.id.au>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On 1/23/19 7:44 AM, Benjamin Herrenschmidt wrote:
> On Tue, 2019-01-22 at 16:23 +1100, Paul Mackerras wrote:
>>
>> Which ones of these could be implemented in QEMU?  Are there any that
>> can't possibly be implemented in QEMU because they need to do things
>> that require calling internal interfaces that userspace doesn't have
>> access to?
> 
> Implementing them in qemu doesn't make a lot of sense. Qemu doesn't
> have access to most of the XIVE HW state. There's a XIVE model for full
> emulation but when using the real thing, almost none of it is visible.
> A lot of those hcalls effectively turn into OPAL calls.
> 
>> How often do we expect each of these hypercalls to be called?
> 
> It depends, I can't tell for AIX. For Linux, not often with one
> exception: H_INT_ESB which will be used whenever you EOI an emulated
> LSI.

yes. This one is only doing loads and stores.

>  .../...
> 
>> Why do we need to provide real-mode versions of these hypercall
>> handlers?  I thought these hypercalls would only get called
>> infrequently, and in any case certainly much less frequently than once
>> per interrupt delivered.  If they are infrequent, then let's leave out
>> the real-mode version and just handle them in book3s_hv.c.
> 
> Agreed with the exception maybe of H_INT_ESB

ok. 

Some of these hcalls are really simple and only getting local info from 
the host (h_int_get_*). I thought handling the hcall ASAP was a preferred 
practice, even if the hcall is not called frequently. Isn't it ?

 
>>> @@ -5153,6 +5169,19 @@ static unsigned int default_hcall_list[] = {
>>>        H_IPOLL,
>>>        H_XIRR,
>>>        H_XIRR_X,
>>> +#endif
>>> +#ifdef CONFIG_KVM_XIVE
>>> +     H_INT_GET_SOURCE_INFO,
>>> +     H_INT_SET_SOURCE_CONFIG,
>>> +     H_INT_GET_SOURCE_CONFIG,
>>> +     H_INT_GET_QUEUE_INFO,
>>> +     H_INT_SET_QUEUE_CONFIG,
>>> +     H_INT_GET_QUEUE_CONFIG,
>>> +     H_INT_SET_OS_REPORTING_LINE,
>>> +     H_INT_GET_OS_REPORTING_LINE,
>>> +     H_INT_ESB,
>>> +     H_INT_SYNC,
>>> +     H_INT_RESET,
>>>   #endif
>>
>> The policy is not to add new hcalls to default_hcall_list[].  Is there
>> a strong reason for adding them here?

I don't remember. I will check for v2.

Thanks, 

C.