Re: [PATCH v3 6/6] x86/vmware: Add TDX hypercall support

[Alexey Makhalov]

On 12/19/23 3:23 PM, kirill.shutemov@xxxxxxxxxxxxxxx wrote:
> On Tue, Dec 19, 2023 at 01:57:51PM -0800, Alexey Makhalov wrote:
> > diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> > index 3aa1adaed18f..ef07ab7a07e1 100644
> > --- a/arch/x86/kernel/cpu/vmware.c
> > +++ b/arch/x86/kernel/cpu/vmware.c
> > @@ -428,6 +428,30 @@ static bool __init vmware_legacy_x2apic_available(void)
> >   		(eax & BIT(VCPU_LEGACY_X2APIC));
> >   }
> >   
> > +#ifdef CONFIG_INTEL_TDX_GUEST
> > +unsigned long vmware_tdx_hypercall(unsigned long cmd,
> > +				   struct tdx_module_args *args)
> > +{
> > +	if (!hypervisor_is_type(X86_HYPER_VMWARE))
> > +		return 0;
> > +
> > +	if (cmd & ~VMWARE_CMD_MASK) {
> > +		pr_warn("Out of range command %x\n", cmd);
> > +		return 0;
>
> Is zero success? Shouldn't it be an error?

VMware hypercalls do not have a standard way of signalling an error.
To generalize expectations from the caller perspective of any existing 
hypercalls: error (including hypercall is not supported or disabled) is 
when return value is 0 and out1/2 are unchanged or equal to in1/in2.

All existing vmware_hypercall callers will gracefully handle returned 0.
But they should never hit this path, as 0 bail out was introduced as a 
protection for the case where exported vmware_tdx_hypercall is used by 
random caller (not following VMware hypercall ABI).

> > +	}
> > +
> > +	args->r10 = VMWARE_TDX_VENDOR_LEAF;
> > +	args->r11 = VMWARE_TDX_HCALL_FUNC;
> > +	args->r12 = VMWARE_HYPERVISOR_MAGIC;
> > +	args->r13 = cmd;
> > +
> > +	__tdx_hypercall(args);
> > +
> > +	return args->r12;
> > +}
> > +EXPORT_SYMBOL_GPL(vmware_tdx_hypercall);
> > +#endif
> > +
> >   #ifdef CONFIG_AMD_MEM_ENCRYPT
> >   static void vmware_sev_es_hcall_prepare(struct ghcb *ghcb,
> >   					struct pt_regs *regs)
> > --
> > 2.39.0