Re: [PATCH v2 20/31] x86/virt/tdx: Add a helper to loop on TDX_INTERRUPTED_RESUMABLE

[Ackerley Tng]

Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx> writes:

> Add a helper to handle SEAMCALL return code TDX_INTERRUPTED_RESUMABLE.
>
> SEAMCALL returns TDX_INTERRUPTED_RESUMABLE to avoid stalling host for
> long time. After host has handled the interrupt, it calls the
> interrupted SEAMCALL again and TDX Module continues to execute. TDX
> Module made progress in this case and would eventually finish. An
> infinite loop in host should be safe.
>
> The helper is for SEAMCALL wrappers which output information by using
> seamcall_ret() or seamcall_saved_ret(). The 2 functions overwrite input
> arguments by outputs but much SEAMCALLs expect the same inputs to

Did you mean most instead of much?

> resume.
>
> The helper is not for special cases where the SEAMCALL expects modified
> inputs to resume. The helper is also not for SEAMCALLs with no output,
> do {...} while (r == TDX_INTERRUPTED_RESUMABLE) just works.
>
> Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/virt/vmx/tdx/tdx.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index cd0948794b6c..294f36048c03 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -2084,6 +2084,29 @@ static inline u64 tdx_tdr_pa(struct tdx_td *td)
>  	return page_to_phys(td->tdr_page);
>  }
>
> +static u64 __maybe_unused __seamcall_ir_resched(sc_func_t sc_func, u64 fn,
> +						struct tdx_module_args *args)
> +{
> +	struct tdx_module_args _args;
> +	u64 r;
> +
> +	while (1) {
> +		_args = *(args);

Is this copying meant to ensure that every retry has the same input
args? Perhaps a comment should be added so it's obvious that every retry
will have the same input, and outputs from each retry are dropped.

> +		r = sc_retry(sc_func, fn, &_args);
> +		if (r != TDX_INTERRUPTED_RESUMABLE)
> +			break;
> +
> +		cond_resched();
> +	}
> +
> +	*args = _args;
> +
> +	return r;
> +}
> +
> +#define seamcall_ret_ir_resched(fn, args)	\
> +	__seamcall_ir_resched(__seamcall_ret, fn, args)
> +
>  noinstr u64 tdh_vp_enter(struct tdx_vp *td, struct tdx_module_args *args)
>  {
>  	args->rcx = td->tdvpr_pa;
> --
> 2.25.1