linux-kernel - Re: [PATCH 07/13] x86/virt/tdx: Add SEAMCALL wrapper tdh_mem_sept

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Message-ID: <b27448f5fc3bc96ae4c166e6eb4886e2ff8b4f90.camel@intel.com>
Date: Thu, 2 Jan 2025 21:59:59 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "Zhao, Yan Y" <yan.y.zhao@...el.com>, "sean.j.christopherson@...el.com"
	<sean.j.christopherson@...el.com>, "Huang, Kai" <kai.huang@...el.com>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "Yamahata,
 Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH 07/13] x86/virt/tdx: Add SEAMCALL wrapper
 tdh_mem_sept_add() to add SEPT pages

On Wed, 2025-01-01 at 02:49 -0500, Paolo Bonzini wrote:
> 
> +u64 tdh_mem_sept_add(struct tdx_td *td, u64 gpa, u64 level, u64 hpa, u64 *rcx, u64 *rdx)
> +{
> +	struct tdx_module_args args = {
> +		.rcx = gpa | level,

The bit packing here is a bit magic. Yan had been looking at adding a union like
below to use internally in tdh_mem_sept_add() to pack the rcx register.

union tdx_sept_gpa_mapping_info {
	struct {
		u64 level	: 3;
		u64 reserved1	: 9;
		u64 gfn		: 40;
		u64 reserved2	: 12;
	};
	u64 full;
};

It might be a bit verbose, but I agree something should be done.


> +		.rdx = tdx_tdr_pa(td),
> +		.r8 = hpa,
> +	};
> +	u64 ret;
> +
> +	clflush_cache_range(__va(hpa), PAGE_SIZE);
> +	ret = seamcall_ret(TDH_MEM_SEPT_ADD, &args);
> +
> +	*rcx = args.rcx;
> +	*rdx = args.rdx;

This was changed to this:
	*extended_err1 = args.rcx;
	*extended_err2 = args.rdx;

The reasoning is rcx and rdx are not very clear names. The caller only uses them
for printing raw error codes, so don't bother creating a union or anything
fancy. The print statements should print the raw error code to help in debugging
situations where new bits are defined and returned by a future buggy TDX module.

> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(tdh_mem_sept_add);
> +
>  u64 tdh_vp_addcx(struct tdx_vp *vp, struct page *tdcx_page)
>  {
>  	struct tdx_module_args args = {
> diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> index 62cb7832c42d..308d3aa565d7 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -16,6 +16,7 @@
>   * TDX module SEAMCALL leaf functions
>   */
>  #define TDH_MNG_ADDCX			1
> +#define TDH_MEM_SEPT_ADD		3
>  #define TDH_VP_ADDCX			4
>  #define TDH_MNG_KEY_CONFIG		8
>  #define TDH_MNG_CREATE			9