linux-kernel - Re: [PATCH 1/4] x86/tdx: Introduce tdg_vm

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Date: Sat, 9 Mar 2024 16:02:58 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com, 
	hpa@...or.com, seanjc@...gle.com, ele.reshetova@...el.com, 
	rick.p.edgecombe@...el.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] x86/tdx: Introduce tdg_vm_wr()

On Sat, Mar 9, 2024 at 1:02 PM Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> Add a helper to write to a TD-scope metadata field and use it to set
> NOTIFY_ENABLES.
>

Add a note about why you create this helper function. I think the
intention is to reuse it
to update other TD-scope fields.

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/coco/tdx/tdx.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index cc67f7380055..5ffe5ef99536 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -77,6 +77,20 @@ static inline void tdcall(u64 fn, struct tdx_module_args *args)
>                 panic("TDCALL %lld failed (Buggy TDX module!)\n", fn);
>  }
>
> +static inline u64 tdg_vm_wr(u64 field, u64 value, u64 mask)
> +{
> +       struct tdx_module_args args = {
> +               .rdx = field,
> +               .r8 = value,
> +               .r9 = mask,
> +       };
> +
> +       tdcall(TDG_VM_WR, &args);
> +
> +       /* Old value */
> +       return args.r8;

Since the update failure will panic, any use for returning the old value?

> +}
> +
>  /**
>   * tdx_mcall_get_report0() - Wrapper to get TDREPORT0 (a.k.a. TDREPORT
>   *                           subtype 0) using TDG.MR.REPORT TDCALL.
> @@ -902,10 +916,6 @@ static void tdx_kexec_unshare_mem(void)
>
>  void __init tdx_early_init(void)
>  {
> -       struct tdx_module_args args = {
> -               .rdx = TDCS_NOTIFY_ENABLES,
> -               .r9 = -1ULL,
> -       };
>         u64 cc_mask;
>         u32 eax, sig[3];
>
> @@ -924,7 +934,7 @@ void __init tdx_early_init(void)
>         cc_set_mask(cc_mask);
>
>         /* Kernel does not use NOTIFY_ENABLES and does not need random #VEs */
> -       tdcall(TDG_VM_WR, &args);
> +       tdg_vm_wr(TDCS_NOTIFY_ENABLES, 0, -1ULL);
>
>         /*
>          * All bits above GPA width are reserved and kernel treats shared bit
> --
> 2.43.0
>