linux-kernel - Re: [PATCH v2 03/10] x86/virt/tdx: Support global metadata read for all element sizes

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Message-ID: <66b1642a825e7_4fc729449@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 5 Aug 2024 16:45:46 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Kai Huang <kai.huang@...el.com>, <dave.hansen@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <bp@...en8.de>, <tglx@...utronix.de>,
	<peterz@...radead.org>, <mingo@...hat.com>, <hpa@...or.com>,
	<seanjc@...gle.com>, <pbonzini@...hat.com>, <dan.j.williams@...el.com>
CC: <x86@...nel.org>, <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<rick.p.edgecombe@...el.com>, <isaku.yamahata@...el.com>,
	<chao.gao@...el.com>, <binbin.wu@...ux.intel.com>, <kai.huang@...el.com>
Subject: Re: [PATCH v2 03/10] x86/virt/tdx: Support global metadata read for
 all element sizes

Kai Huang wrote:
> The TDX module provides "global metadata fields" for software to query.
> Each metadata field is accessible by a unique "metadata field ID".  TDX
> supports 8/16/32/64 bits metadata element sizes.  The size of each
> metadata field is encoded in its associated metadata field ID.
> 
> For now the kernel only reads "TD Memory Region" (TDMR) related global
> metadata fields for module initialization.  All these metadata fields
> are 16-bit, and the kernel only supports reading 16-bit fields.
> 
> Future changes will need to read more metadata fields with other element
> sizes.  To resolve this once for all, extend the existing metadata
> reading code to support reading all element sizes.
> 
> Signed-off-by: Kai Huang <kai.huang@...el.com>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
> 
> v1 -> v2 (Nikolay):
>  - MD_FIELD_BYTES() -> MD_FIELD_ELE_SIZE().
>  - 'bytes' -> 'size' in stbuf_read_sysmd_field().
> 
> ---
>  arch/x86/virt/vmx/tdx/tdx.c | 29 ++++++++++++++++-------------
>  arch/x86/virt/vmx/tdx/tdx.h |  3 ++-
>  2 files changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 2ce03c3ea017..4644b324ff86 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -270,23 +270,25 @@ static int read_sys_metadata_field(u64 field_id, u64 *data)
>  	return 0;
>  }
>  
> -static int read_sys_metadata_field16(u64 field_id,
> -				     int offset,
> -				     void *stbuf)
> +/*
> + * Read one global metadata field and store the data to a location of a
> + * given buffer specified by the offset and size (in bytes).
> + */
> +static int stbuf_read_sysmd_field(u64 field_id, void *stbuf, int offset,
> +				  int size)
>  {
> -	u16 *member = stbuf + offset;
> +	void *member = stbuf + offset;
>  	u64 tmp;
>  	int ret;
>  
> -	if (WARN_ON_ONCE(MD_FIELD_ID_ELE_SIZE_CODE(field_id) !=
> -			MD_FIELD_ID_ELE_SIZE_16BIT))
> +	if (WARN_ON_ONCE(MD_FIELD_ELE_SIZE(field_id) != size))
>  		return -EINVAL;

Per the last patch, re: unrolling @fields, it's unfortunate to have a
runtime warning for something that could have been verified at compile
time.