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

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Date: Tue, 19 Dec 2023 16:27:51 -0800
From: Alexey Makhalov <alexey.makhalov@...adcom.com>
To: kirill.shutemov@...ux.intel.com
Cc: linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
 bp@...en8.de, hpa@...or.com, dave.hansen@...ux.intel.com, mingo@...hat.com,
 tglx@...utronix.de, x86@...nel.org, netdev@...r.kernel.org,
 richardcochran@...il.com, linux-input@...r.kernel.org,
 dmitry.torokhov@...il.com, zackr@...are.com,
 linux-graphics-maintainer@...are.com, pv-drivers@...are.com,
 namit@...are.com, timothym@...are.com, akaher@...are.com, jsipek@...are.com,
 dri-devel@...ts.freedesktop.org, daniel@...ll.ch, airlied@...il.com,
 tzimmermann@...e.de, mripard@...nel.org, maarten.lankhorst@...ux.intel.com,
 horms@...nel.org
Subject: Re: [PATCH v3 6/6] x86/vmware: Add TDX hypercall support



On 12/19/23 3:23 PM, kirill.shutemov@...ux.intel.com 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
>>
>