RE: [PATCH 4/4] asm-generic/hyperv: Add definitions for Get/SetVpRegister hypercalls

[Michael Kelley <mikelley@microsoft.com>]

From: Michael Kelley Sent: Tuesday, April 21, 2020 8:50 AM
> 
> From: Vitaly Kuznetsov <vkuznets@redhat.com> Sent: Tuesday, April 21, 2020 6:03 AM
> >
> > Michael Kelley <mikelley@microsoft.com> writes:
> >
> > > Add definitions for GetVpRegister and SetVpRegister hypercalls, which
> > > are implemented for both x86 and ARM64.
> > >
> > > Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> > > ---
> > >  include/asm-generic/hyperv-tlfs.h | 28 ++++++++++++++++++++++++++++
> > >  1 file changed, 28 insertions(+)
> > >
> > > diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> > > index 1f92ef92eb56..29b60f5b6323 100644
> > > --- a/include/asm-generic/hyperv-tlfs.h
> > > +++ b/include/asm-generic/hyperv-tlfs.h
> > > @@ -141,6 +141,8 @@ struct ms_hyperv_tsc_page {
> > >  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX	0x0013
> > >  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX	0x0014
> > >  #define HVCALL_SEND_IPI_EX			0x0015
> > > +#define HVCALL_GET_VP_REGISTERS			0x0050
> > > +#define HVCALL_SET_VP_REGISTERS			0x0051
> > >  #define HVCALL_POST_MESSAGE			0x005c
> > >  #define HVCALL_SIGNAL_EVENT			0x005d
> > >  #define HVCALL_RETARGET_INTERRUPT		0x007e
> > > @@ -439,4 +441,30 @@ struct hv_retarget_device_interrupt {
> > >  	struct hv_device_interrupt_target int_target;
> > >  } __packed __aligned(8);
> > >
> > > +
> > > +/* HvGetVPRegister hypercall */
> >
> > Nit: 'HvGetVpRegisters' in TLFS
> >
> > > +struct hv_get_vp_register_input {
> >
> > Nit: I would also to name it 'hv_get_vp_registers_input' (plural, like
> > the hypercall).
> >
> > > +	u64 partitionid;
> > > +	u32 vpindex;
> > > +	u8  inputvtl;
> > > +	u8  padding[3];
> > > +	u32 name0;
> > > +	u32 name1;
> > > +} __packed;
> >
> > Isn't it a REP hypercall where we can we can pass a list? In that case
> > this should look like
> >
> > struct hv_get_vp_registers_input {
> > 	struct {
> > 		u64 partitionid;
> > 		u32 vpindex;
> > 		u8  inputvtl;
> > 		u8  padding[3];
> >         } header;
> > 	struct {
> > 		u32 name0;
> > 		u32 name1;
> >         } elem[];
> > } __packed;
> >
> > > +
> > > +struct hv_get_vp_register_output {
> >
> > Ditto.

I've sent out a new version, but didn't change
hv_get_vp_register_output except to make
it hv_get_vp_registers_output.   The C compiler
wont' let me put a  variable size array as the
only field in the struct.

> >
> > > +	union {
> > > +		struct {
> > > +			u32 a;
> > > +			u32 b;
> >  > +			u32 c;
> > > +			u32 d;
> > > +		} as32 __packed;
> > > +		struct {
> > > +			u64 low;
> > > +			u64 high;
> > > +		} as64 __packed;
> > > +	};
> > > +};
> >
> > I'm wondering why you define both
> > HVCALL_GET_VP_REGISTERS/HVCALL_SET_VP_REGISTERS but only add 'struct
> > hv_get_vp_register_input' and not 'struct hv_set_vp_register_input'.
> >
> > The later should look similar, AFAIU it is:
> >
> > struct hv_set_vp_registers_input {
> > 	struct {
> > 		u64 partitionid;
> > 		u32 vpindex;
> > 		u8  inputvtl;
> > 		u8  padding[3];
> >         } header;
> > 	struct {
> > 		u32 name;
> > 		u32 padding1;
> > 		u64 padding2; //not sure this is not a mistake in TLFS

The additional padding is not a mistake.  Hyper-V wants
the register value to be aligned to 128 bits even though
it is described in the TLFS document as two 64 bit fields.

> >             	u64 regvallow;
> >             	u64 regvalhigh;
> > 	} elem[];
> > } __packed;
> >
> > > +
> > >  #endif
> >

Michael