Re: [RFC PATCH V5 03/15] x86/hyperv: Set Virtual Trust Level in VMBus init message

[Tianyu Lan]

On 5/2/2023 12:30 PM, Zhi Wang wrote:
> On Mon,  1 May 2023 04:57:13 -0400
> Tianyu Lan <ltykernel@xxxxxxxxx> wrote:
>
> > From: Tianyu Lan <tiala@xxxxxxxxxxxxx>
> >
> > sev-snp guest provides vtl(Virtual Trust Level) and
> > get it from hyperv hvcall via HVCALL_GET_VP_REGISTERS.
> > Set target vtl in the VMBus init message.
> >
> > Signed-off-by: Tianyu Lan <tiala@xxxxxxxxxxxxx>
> > ---
> > Change since RFC v4:
> >         * Use struct_size to calculate array size.
> >         * Fix some coding style
> >
> > Change since RFC v3:
> >         * Use the standard helper functions to check hypercall result
> >         * Fix coding style
> >
> > Change since RFC v2:
> >         * Rename get_current_vtl() to get_vtl()
> >         * Fix some coding style issues
> > ---
> >   arch/x86/hyperv/hv_init.c          | 36 ++++++++++++++++++++++++++++++
> >   arch/x86/include/asm/hyperv-tlfs.h |  7 ++++++
> >   drivers/hv/connection.c            |  1 +
> >   include/asm-generic/mshyperv.h     |  1 +
> >   include/linux/hyperv.h             |  4 ++--
> >   5 files changed, 47 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > index 9f3e2d71d015..331b855314b7 100644
> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -384,6 +384,40 @@ static void __init hv_get_partition_id(void)
> >   	local_irq_restore(flags);
> >   }
> >   
> > +static u8 __init get_vtl(void)
> > +{
> > +	u64 control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_REGISTERS;
> > +	struct hv_get_vp_registers_input *input;
> > +	struct hv_get_vp_registers_output *output;
> > +	u64 vtl = 0;
> > +	u64 ret;
> > +	unsigned long flags;
> > +
> > +	local_irq_save(flags);
> > +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> > +	output = (struct hv_get_vp_registers_output *)input;
>
> ===
> > +	if (!input) {
> > +		local_irq_restore(flags);
> > +		goto done;
> > +	}
> > +
> ===
> Is this really necessary?
>
> drivers/hv/hv_common.c:
>
>          hyperv_pcpu_input_arg = alloc_percpu(void  *);
>          BUG_ON(!hyperv_pcpu_input_arg);

Hi Zhi:
	The hyperv_pcpu_input_arg is a point to address of input arg
pages and these pages are allocated in the hv_common_cpu_init(). If
it failed to allocate these pages, the value pointed by 
hyperv_pcpu_input_arg will be NULL.