linux-kernel - Re: [PATCH v19 004/130] x86/virt/tdx: Support global metadata read for all element sizes

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Date: Mon, 26 Feb 2024 15:32:50 +0100
From: Juergen Gross <jgross@...e.com>
To: isaku.yamahata@...el.com, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com
Subject: Re: [PATCH v19 004/130] x86/virt/tdx: Support global metadata read
 for all element sizes

On 26.02.24 09:25, isaku.yamahata@...el.com wrote:
> From: Kai Huang <kai.huang@...el.com>
> 
> For now the kernel only reads TDMR related global metadata fields for
> module initialization.  All these fields are 16-bits, and the kernel
> only supports reading 16-bits fields.
> 
> KVM will need to read a bunch of non-TDMR related metadata to create and
> run TDX guests.  It's essential to provide a generic metadata read
> infrastructure which supports reading all 8/16/32/64 bits element sizes.
> 
> Extend the metadata read to support reading all these element sizes.
> 
> Signed-off-by: Kai Huang <kai.huang@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>   arch/x86/virt/vmx/tdx/tdx.c | 59 +++++++++++++++++++++++++------------
>   arch/x86/virt/vmx/tdx/tdx.h |  2 --
>   2 files changed, 40 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index eb208da4ff63..a19adc898df6 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -271,23 +271,35 @@ 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)
> +/* Return the metadata field element size in bytes */
> +static int get_metadata_field_bytes(u64 field_id)
>   {
> -	u16 *st_member = stbuf + offset;
> +	/*
> +	 * TDX supports 8/16/32/64 bits metadata field element sizes.
> +	 * TDX module determines the metadata element size based on the
> +	 * "element size code" encoded in the field ID (see the comment
> +	 * of MD_FIELD_ID_ELE_SIZE_CODE macro for specific encodings).
> +	 */
> +	return 1 << MD_FIELD_ID_ELE_SIZE_CODE(field_id);
> +}
> +
> +static int stbuf_read_sys_metadata_field(u64 field_id,
> +					 int offset,
> +					 int bytes,
> +					 void *stbuf)
> +{
> +	void *st_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(get_metadata_field_bytes(field_id) != bytes))
>   		return -EINVAL;
>   
>   	ret = read_sys_metadata_field(field_id, &tmp);
>   	if (ret)
>   		return ret;
>   
> -	*st_member = tmp;
> +	memcpy(st_member, &tmp, bytes);
>   
>   	return 0;
>   }
> @@ -295,11 +307,30 @@ static int read_sys_metadata_field16(u64 field_id,
>   struct field_mapping {
>   	u64 field_id;
>   	int offset;
> +	int size;
>   };
>   
>   #define TD_SYSINFO_MAP(_field_id, _struct, _member)	\
>   	{ .field_id = MD_FIELD_ID_##_field_id,		\
> -	  .offset   = offsetof(_struct, _member) }
> +	  .offset   = offsetof(_struct, _member),	\
> +	  .size     = sizeof(typeof(((_struct *)0)->_member)) }
> +
> +static int read_sys_metadata(struct field_mapping *fields, int nr_fields,

The first parameter should be "const struct field_mapping *fields".


Juergen

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