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

Zhi Wang
2023-05-04T15:58:47Z

On Thu, 4 May 2023 08:38:46 -0700
Tianyu Lan <ltykernel@gmail.com> wrote:

> On 5/2/2023 12:30 PM, Zhi Wang wrote:
> > On Mon, 1 May 2023 04:57:13 -0400
> > Tianyu Lan <ltykernel@gmail.com> wrote:
> >
> >> From: Tianyu Lan <tiala@microsoft.com>
> >>
> >> 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@microsoft.com>
> >> ---
> >> 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.
>

Sorry, it seems my email editor dropped some text. I was wondering that
if the check above is necessary as there is a BUG_ON() when allocating
hyperv_pcpu_input_arg.

So when coming to get_vtl(), the hyperv_pcpu_input_arg should not be NULL.
(Guarded by the BUG_ON() in the allocation)?