linux-kernel - Re: [PATCH 6/9] x86/virt/tdx: Start to track all global metadata in one structure

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Date: Tue, 18 Jun 2024 16:17:45 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org
Cc: x86@...nel.org, dave.hansen@...el.com, dan.j.williams@...el.com,
 kirill.shutemov@...ux.intel.com, rick.p.edgecombe@...el.com,
 peterz@...radead.org, tglx@...utronix.de, bp@...en8.de, mingo@...hat.com,
 hpa@...or.com, seanjc@...gle.com, pbonzini@...hat.com, kvm@...r.kernel.org,
 isaku.yamahata@...el.com, binbin.wu@...ux.intel.com
Subject: Re: [PATCH 6/9] x86/virt/tdx: Start to track all global metadata in
 one structure



On 16.06.24 г. 15:01 ч., Kai Huang wrote:
> The TDX module provides a set of "global metadata fields".  They report
> things like TDX module version, supported features, and fields related
> to create/run TDX guests and so on.
> 
> Currently the kernel only reads "TD Memory Region" (TDMR) related fields
> for module initialization.  There are immediate needs which require the
> TDX module initialization to read more global metadata including module
> version, supported features and "Convertible Memory Regions" (CMRs).
> 
> Also, KVM will need to read more metadata fields to support baseline TDX
> guests.  In the longer term, other TDX features like TDX Connect (which
> supports assigning trusted IO devices to TDX guest) may also require
> other kernel components such as pci/vt-d to access global metadata.
> 
> To meet all those requirements, the idea is the TDX host core-kernel to
> to provide a centralized, canonical, and read-only structure for the
> global metadata that comes out from the TDX module for all kernel
> components to use.
> 
> As the first step, introduce a new 'struct tdx_sysinfo' to track all
> global metadata fields.
> 
> TDX categories global metadata fields into different "Class"es.  E.g.,
> the current TDMR related fields are under class "TDMR Info".  Instead of
> making 'struct tdx_sysinfo' a plain structure to contain all metadata
> fields, organize them in smaller structures based on the "Class".
> 
> This allows those metadata fields to be used in finer granularity thus
> makes the code more clear.  E.g., the current construct_tdmr() can just
> take the structure which contains "TDMR Info" metadata fields.
> 
> Start with moving 'struct tdx_tdmr_sysinfo' to 'struct tdx_sysinfo', and
> rename 'struct tdx_tdmr_sysinfo' to 'struct tdx_sysinfo_tdmr_info' to
> make it consistent with the "class name".
> 
> Add a new function get_tdx_sysinfo() as the place to read all metadata
> fields, and call it at the beginning of init_tdx_module().  Move the
> existing get_tdx_tdmr_sysinfo() to get_tdx_sysinfo().
> 
> Note there is a functional change: get_tdx_tdmr_sysinfo() is moved from
> after build_tdx_memlist() to before it, but it is fine to do so.

Why? I don't see build_tdx_memlist() using any tdmr data.

> 
> Signed-off-by: Kai Huang <kai.huang@...el.com>

This patch semantically does 3 independent things :

1. Renames tdx_tdmr_sysinfo to tdx_sysinfo_tdmr_info
2. Introduces tdx_sysinfo and puts the aforementioned struct in it.
3. Moves get_tdx_tdmr_sysinfo

> ---
>   arch/x86/virt/vmx/tdx/tdx.c | 29 +++++++++++++++++------------
>   arch/x86/virt/vmx/tdx/tdx.h | 32 +++++++++++++++++++++++++-------
>   2 files changed, 42 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index fad42014ca37..4683884efcc6 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -320,11 +320,11 @@ static int stbuf_read_sysmd_multi(const struct field_mapping *fields,
>   }
>   
>   #define TD_SYSINFO_MAP_TDMR_INFO(_field_id, _member)	\
> -	TD_SYSINFO_MAP(_field_id, struct tdx_tdmr_sysinfo, _member)
> +	TD_SYSINFO_MAP(_field_id, struct tdx_sysinfo_tdmr_info, _member)
>   
> -static int get_tdx_tdmr_sysinfo(struct tdx_tdmr_sysinfo *tdmr_sysinfo)
> +static int get_tdx_tdmr_sysinfo(struct tdx_sysinfo_tdmr_info *tdmr_sysinfo)
>   {
> -	/* Map TD_SYSINFO fields into 'struct tdx_tdmr_sysinfo': */
> +	/* Map TD_SYSINFO fields into 'struct tdx_sysinfo_tdmr_info': */
>   	static const struct field_mapping fields[] = {
>   		TD_SYSINFO_MAP_TDMR_INFO(MAX_TDMRS,		max_tdmrs),
>   		TD_SYSINFO_MAP_TDMR_INFO(MAX_RESERVED_PER_TDMR, max_reserved_per_tdmr),
> @@ -337,6 +337,11 @@ static int get_tdx_tdmr_sysinfo(struct tdx_tdmr_sysinfo *tdmr_sysinfo)
>   	return stbuf_read_sysmd_multi(fields, ARRAY_SIZE(fields), tdmr_sysinfo);
>   }
>   
> +static int get_tdx_sysinfo(struct tdx_sysinfo *sysinfo)

What's the point of this function, directly calling 
get_tdx_tdmr_sysinfo(&sysinfo->tdmr_info); isn't any less obvious.

> +{
> +	return get_tdx_tdmr_sysinfo(&sysinfo->tdmr_info);
> +}
> +
>   /* Calculate the actual TDMR size */
>   static int tdmr_size_single(u16 max_reserved_per_tdmr)
>   {

<snip>