Re: [RFC PATCH 14/15] x86/tdx: Add TDG.DMAR.ACCEPT module call wrapper for TDX Connect

[Xiaoyao Li]

On 9/24/2026 12:10 PM, Zhenzhong Duan wrote:
> TDG.DMAR.ACCEPT updates the PASID table entry of the TDI as present to
> allow DMA access to the TD private memory.
> 
> For TDG.DMAR.ACCEPT, the R8-R15 input registers are reserved and must
> be zero. Use a zero-initialized argument structure with __tdcall_saved()
> so the complete TDCALL input register set is loaded with the required
> values.
> 
> Translate TDX module return codes into Linux errno values.
> 
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxx>
> ---
>  arch/x86/coco/tdx/tdx_connect.c   | 28 ++++++++++++++++++++++++++++
>  arch/x86/include/asm/shared/tdx.h |  1 +
>  arch/x86/include/asm/tdx.h        |  1 +
>  3 files changed, 30 insertions(+)
> 
> diff --git a/arch/x86/coco/tdx/tdx_connect.c b/arch/x86/coco/tdx/tdx_connect.c
> index 3ef10b1df401..a03b1da9a52a 100644
> --- a/arch/x86/coco/tdx/tdx_connect.c
> +++ b/arch/x86/coco/tdx/tdx_connect.c
> @@ -136,3 +136,31 @@ int tdx_mcall_tdi_start(u64 func_id, u64 exp_bind_session)
>  	return tdx_mcall_tdi_to_errno(ret);
>  }
>  EXPORT_SYMBOL_FOR_MODULES(tdx_mcall_tdi_start, "tdx-guest");
> +
> +/**
> + * tdx_mcall_dmar_accept() - Accept PASID table entry of a TDI instance
> + * @func_id: Function identifier specifying the TDI instance
> + * @target: DMAR target, 0 for non-partitioned TD or L1, 1-3 for L2 VM1-VM3,
> + *          other value reserved
> + *

Linux doesn't support TD partition and the next patch just hard codes it to 0.
We can drop it entirely for simplicity.

> + * Update the PASID table entry of the TDI to mark the DMA Remapping (DMAR)
> + * state as present, allowing DMA access to the TD private memory.
> + *
> + * Return 0 on success, -ENXIO for invalid operands, -EBUSY for busy operation,
> + * -ENODEV for TDI not present or invalid metadata, or -EIO on other TDCALL failures.
> + */
> +int tdx_mcall_dmar_accept(u64 func_id, u64 target)
> +{
> +	struct tdx_module_args args = {
> +		.rcx = func_id,
> +		.rdx = target,
> +	};
> +	u64 ret;
> +
> +	ret = __tdcall_saved(TDG_DMAR_ACCEPT, &args);
> +	if (!ret)
> +		return 0;
> +
> +	return tdx_mcall_tdi_to_errno(ret);
> +}
> +EXPORT_SYMBOL_FOR_MODULES(tdx_mcall_dmar_accept, "tdx-guest");
> diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
> index 90f2842f4253..01387f6b24b3 100644
> --- a/arch/x86/include/asm/shared/tdx.h
> +++ b/arch/x86/include/asm/shared/tdx.h
> @@ -22,6 +22,7 @@
>  #define TDG_VM_WR			8
>  #define TDG_TDI_READ			67
>  #define TDG_TDI_START			68
> +#define TDG_DMAR_ACCEPT			70
>  #define TDG_MMIO_ACCEPT			71
>  
>  /* TDX TD attributes */
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 787b3039ef5a..118cc58cc909 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -157,6 +157,7 @@ u64 tdx_hcall_tdcm(u16 devid, void *buf, size_t size, u8 vector);
>  int tdx_mcall_tdi_read(u64 func_id, u64 field, u64 *value);
>  int tdx_mcall_mmio_accept(u64 func_id, u64 index, u32 pg_offset, u32 page_cnt, phys_addr_t gpa);
>  int tdx_mcall_tdi_start(u64 func_id, u64 exp_bind_session);
> +int tdx_mcall_dmar_accept(u64 func_id, u64 target);
>  #endif
>  
>  void __init tdx_dump_attributes(u64 td_attr);