Re: [Qemu-ppc] [PATCH v3] spapr: add splpar hcalls H_PROD, H_CONFER

[Nicholas Piggin]

David Gibson's on April 17, 2019 10:47 pm:
> On Wed, Apr 17, 2019 at 02:01:29PM +0200, Greg Kurz wrote:
>> On Wed, 17 Apr 2019 21:20:00 +1000
>> Nicholas Piggin <address@hidden> wrote:
>> > [...]
>> > >> @@ -1860,6 +1928,9 @@ static void hypercall_register_types(void)
>> > >>      /* hcall-splpar */
>> > >>      spapr_register_hypercall(H_REGISTER_VPA, h_register_vpa);
>> > >>      spapr_register_hypercall(H_CEDE, h_cede);
>> > >> +    spapr_register_hypercall(H_CONFER, h_confer);
>> > >> +    spapr_register_hypercall(H_PROD, h_prod);
>> > >> +
>> > >>      spapr_register_hypercall(H_SIGNAL_SYS_RESET, h_signal_sys_reset);  
>> > > 
>> > > You're no longer enabling the KVM CONFER and PROD hypercalls.  Are
>> > > they enabled by default, or is that an intentional change?  
>> > 
>> 
>> AFAICT they seem to be enabled by default in HV KVM.
>> 
>> > Oh, it was not intentional, I must not understand how this works. Why
>> > is this no longer enabling the those hcalls?
>> > 
>> 
>> Since linux commit 699a0ea0823d ("KVM: PPC: Book3S: Controls for in-kernel 
>> sPAPR hypercall handling"), in-kernel hypercalls are disabled by default
>> and must be explicitely enabled by userspace. QEMU does that for some
>> hypercalls already (search kvmppc_enable_set_mode_hcall() in QEMU for an
>> example).
>> 
>> Since H_CONFER and H_PROD are listed in default_hcall_list[] in book3s_hv.c,
>> no need for QEMU to enable them in KVM.
> 
> Ah, ok.  Oops, that means the guest environment has been visibly
> different for KVM and TCG all this time, which isn't great.
> 
>> Not sure about David's "no longer" wording though.
> 
> 
> "no longer" meaning the previous patch version had some
> kvmppc_enable_hcall(), but this version doesn't.

Let me do one more iteration with the comment fixed up at least,
and I'll do a bit of testing with KVM vs TCG behaviour and see
if there are any problems around this.

Thanks,
Nick