linux-kernel - Re: [PATCH v6 01/21] x86/tdx: Use enum to define page level of TDX supported page sizes

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Date:   Thu, 27 Oct 2022 15:08:00 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     linux-mm@...ck.org, seanjc@...gle.com, pbonzini@...hat.com,
        dave.hansen@...el.com, dan.j.williams@...el.com,
        rafael.j.wysocki@...el.com, kirill.shutemov@...ux.intel.com,
        reinette.chatre@...el.com, len.brown@...el.com,
        tony.luck@...el.com, peterz@...radead.org, ak@...ux.intel.com,
        isaku.yamahata@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, bagasdotme@...il.com,
        sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v6 01/21] x86/tdx: Use enum to define page level of TDX
 supported page sizes

On 10/27/2022 7:16 AM, Kai Huang wrote:
> TDX supports 4K, 2M and 1G page sizes.  When TDX guest accepts one page
> via try_accept_one(), it passes the page size level to the TDX module.
> Currently try_accept_one() uses hard-coded magic number for that.
> 
> Introduce a new enum type to represent the page level of TDX supported
> page sizes to replace the hard-coded values.  Both initializing the TDX
> module and KVM TDX support will need to use that too.
> 
> Also, currently try_accept_one() uses an open-coded switch statement to
> get the TDX page level from the kernel page level.  As KVM will also
> need to do the same thing, introduce a common helper to convert the
> kernel page level to the TDX page level.
> 
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Kai Huang <kai.huang@...el.com>
> ---
>   arch/x86/coco/tdx/tdx.c    | 20 ++++----------------
>   arch/x86/include/asm/tdx.h | 33 +++++++++++++++++++++++++++++++++
>   2 files changed, 37 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 928dcf7a20d9..c5ff9647213d 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -655,7 +655,6 @@ static bool try_accept_one(phys_addr_t *start, unsigned long len,
>   {
>   	unsigned long accept_size = page_level_size(pg_level);
>   	u64 tdcall_rcx;
> -	u8 page_size;
>   
>   	if (!IS_ALIGNED(*start, accept_size))
>   		return false;
> @@ -663,27 +662,16 @@ static bool try_accept_one(phys_addr_t *start, unsigned long len,
>   	if (len < accept_size)
>   		return false;
>   
> +	/* TDX only supports 4K/2M/1G page sizes */

yes, a page can be mapped as 1G size to TD via secure/shared EPT. But 
for this particular TDX_ACCEPT_PAGE case, it only supports 4K and 2M 
currently, which is defined in TDX module spec.

This also implies one thing can be improved in current kernel that 
trying accepting a page from 1G in tdx_enc_status_changed() can be 
optimized to from 2M. It can be changed to start from 1G when TDX 
supports accepting 1G page directly.

> +	if (pg_level < PG_LEVEL_4K || pg_level > PG_LEVEL_1G)
> +		return false;
>   	/*
>   	 * Pass the page physical address to the TDX module to accept the
>   	 * pending, private page.
>   	 *
>   	 * Bits 2:0 of RCX encode page size: 0 - 4K, 1 - 2M, 2 - 1G.

Maybe the “page size” can be adjusted to “TDX page level” accordingly.

>   	 */
> -	switch (pg_level) {
> -	case PG_LEVEL_4K:
> -		page_size = 0;
> -		break;
> -	case PG_LEVEL_2M:
> -		page_size = 1;
> -		break;
> -	case PG_LEVEL_1G:
> -		page_size = 2;
> -		break;
> -	default:
> -		return false;
> -	}
> -
> -	tdcall_rcx = *start | page_size;
> +	tdcall_rcx = *start | to_tdx_pg_level(pg_level);
>   	if (__tdx_module_call(TDX_ACCEPT_PAGE, tdcall_rcx, 0, 0, 0, NULL))
>   		return false;
>   
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 020c81a7c729..1c166fb9c22f 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -20,6 +20,39 @@
>   
>   #ifndef __ASSEMBLY__
>   
> +#include <asm/pgtable_types.h>
> +
> +/*
> + * The page levels of TDX supported page sizes (4K/2M/1G).
> + *
> + * Those values are part of the TDX module ABI.  Do not change them.
> + */
> +enum tdx_pg_level {
> +	TDX_PG_LEVEL_4K,
> +	TDX_PG_LEVEL_2M,
> +	TDX_PG_LEVEL_1G,
> +	TDX_PG_LEVEL_NUM
> +};
> +
> +/*
> + * Get the TDX page level based on the kernel page level.  The caller
> + * to make sure only pass 4K/2M/1G kernel page level.
> + */
> +static inline enum tdx_pg_level to_tdx_pg_level(enum pg_level pglvl)
> +{
> +	switch (pglvl) {
> +	case PG_LEVEL_4K:
> +		return TDX_PG_LEVEL_4K;
> +	case PG_LEVEL_2M:
> +		return TDX_PG_LEVEL_2M;
> +	case PG_LEVEL_1G:
> +		return TDX_PG_LEVEL_1G;
> +	default:
> +		WARN_ON_ONCE(1);
> +	}
> +	return TDX_PG_LEVEL_NUM;
> +}
> +
>   /*
>    * Used to gather the output registers values of the TDCALL and SEAMCALL
>    * instructions when requesting services from the TDX module.