Re: [RFC PATCH 15/15] virt: tdx-guest: Accept default DMAR entry during PCI driver attach

[Xiaoyao Li]

On 9/24/2026 12:10 PM, Zhenzhong Duan wrote:
> Before a TDI can perform DMA to guest private memory, its secure DMA
> mapping must be accepted. This happens during driver load stage after
> MMIO acceptance and TDI activation.
> 
> The enable_dma callback issues TDG.DMAR.ACCEPT to set secure PASID
> table entry to present state and target non-partitioned TD.
> 
> The secure PASID table entry is cleared in unlock stage implicitly
> so disable_dma is a no-op currently.
> 
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxx>
> ---
>  drivers/virt/coco/tdx-guest/connect.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/virt/coco/tdx-guest/connect.c b/drivers/virt/coco/tdx-guest/connect.c
> index a9d41fd38b64..b328caac0a49 100644
> --- a/drivers/virt/coco/tdx-guest/connect.c
> +++ b/drivers/virt/coco/tdx-guest/connect.c
> @@ -427,10 +427,26 @@ static int tdx_devsec_run(struct pci_dev *pdev)
>  	return 0;
>  }
>  
> +static int tdx_devsec_enable_dma(struct pci_dev *pdev)
> +{
> +	int ret = tdx_mcall_dmar_accept(pci_dev_id(pdev), 0);

after going through the series, I have a basic question on guest function_id.

Per TDX connect API spec, TDG.DMAR.ACCEPT, TDG.DMAR.RELEASE,
TDG.TDI.MMIO.ACCEPT, TDG.TDI.RD and TDG.TDI.START all require guest function_id
as input parameter. However, the guest function_id is specified by the host VMM
on TDH.TDI.CREATE.

So how can the guest ensure pci_dev_id(pdev) is the value that will be specified
by the host VMM?

This is a strong contract, while this series doesn't mention it at all.