linux-kernel - Re: [PATCH RFC 1/7] x86/virt/tdx: Add SEAMCALL wrapper to enter/exit TDX guest

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Message-ID: <56db8257-6da2-400d-8306-6e21d9af81f8@intel.com>
Date: Mon, 25 Nov 2024 15:40:10 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Dave Hansen <dave.hansen@...el.com>, pbonzini@...hat.com,
 seanjc@...gle.com, kvm@...r.kernel.org, dave.hansen@...ux.intel.com
Cc: rick.p.edgecombe@...el.com, kai.huang@...el.com,
 reinette.chatre@...el.com, xiaoyao.li@...el.com,
 tony.lindgren@...ux.intel.com, binbin.wu@...ux.intel.com,
 dmatlack@...gle.com, isaku.yamahata@...el.com, nik.borisov@...e.com,
 linux-kernel@...r.kernel.org, x86@...nel.org, yan.y.zhao@...el.com,
 chao.gao@...el.com, weijiang.yang@...el.com
Subject: Re: [PATCH RFC 1/7] x86/virt/tdx: Add SEAMCALL wrapper to enter/exit
 TDX guest

On 22/11/24 18:33, Dave Hansen wrote:
> On 11/22/24 03:10, Adrian Hunter wrote:
>> +struct tdh_vp_enter_tdcall {
>> +	u64	reg_mask	: 32,
>> +		vm_idx		:  2,
>> +		reserved_0	: 30;
>> +	u64	data[TDX_ERR_DATA_PART_2];
>> +	u64	fn;	/* Non-zero for hypercalls, zero otherwise */
>> +	u64	subfn;
>> +	union {
>> +		struct tdh_vp_enter_vmcall 		vmcall;
>> +		struct tdh_vp_enter_gettdvmcallinfo	gettdvmcallinfo;
>> +		struct tdh_vp_enter_mapgpa		mapgpa;
>> +		struct tdh_vp_enter_getquote		getquote;
>> +		struct tdh_vp_enter_reportfatalerror	reportfatalerror;
>> +		struct tdh_vp_enter_cpuid		cpuid;
>> +		struct tdh_vp_enter_mmio		mmio;
>> +		struct tdh_vp_enter_hlt			hlt;
>> +		struct tdh_vp_enter_io			io;
>> +		struct tdh_vp_enter_rd			rd;
>> +		struct tdh_vp_enter_wr			wr;
>> +	};
>> +};
> 
> Let's say someone declares this:
> 
> struct tdh_vp_enter_mmio {
> 	u64	size;
> 	u64	mmio_addr;
> 	u64	direction;
> 	u64	value;
> };
> 
> How long is that going to take you to debug?

When adding a new hardware definition, it would be sensible
to check the hardware definition first before checking anything
else.

However, to stop existing members being accidentally moved,
could add:

#define CHECK_OFFSETS_EQ(reg, member) \
	BUILD_BUG_ON(offsetof(struct tdx_module_args, reg) != offsetof(union tdh_vp_enter_args, member));

	CHECK_OFFSETS_EQ(r12, tdcall.mmio.size);
	CHECK_OFFSETS_EQ(r13, tdcall.mmio.direction);
	CHECK_OFFSETS_EQ(r14, tdcall.mmio.mmio_addr);
	CHECK_OFFSETS_EQ(r15, tdcall.mmio.value);