Re: [PATCH v4 04/24] x86/virt/seamldr: Introduce a wrapper for P-SEAMLDR SEAMCALLs

[Huang, Kai]

On Thu, 2026-02-12 at 06:35 -0800, Chao Gao wrote:
> The TDX architecture uses the "SEAMCALL" instruction to communicate with
> SEAM mode software. Right now, the only SEAM mode software that the kernel
> communicates with is the TDX module. But, there is actually another
> component that runs in SEAM mode but it is separate from the TDX module:
> the persistent SEAM loader or "P-SEAMLDR". Right now, the only component
> that communicates with it is the BIOS which loads the TDX module itself at
> boot. But, to support updating the TDX module, the kernel now needs to be
> able to talk to it.
> 
> P-SEAMLDR SEAMCALLs differ from TDX Module SEAMCALLs in areas such as
> concurrency requirements. Add a P-SEAMLDR wrapper to handle these
> differences and prepare for implementing concrete functions.
> 
> Note that unlike P-SEAMLDR, there is also a non-persistent SEAM loader
> ("NP-SEAMLDR"). This is an authenticated code module (ACM) that is not
> callable at runtime. Only BIOS launches it to load P-SEAMLDR at boot;

[...]

> the kernel does not interact with it.

Nit:

Again, to me this only describes what does the kernel do today.  It doesn't
describe what the kernel needs to do for runtime updating.

Maybe it can just be something like:

  The kernel does not need to interact with it for runtime update.

But I don't know why do you even need to talk about NP-SEAMLDR.

> 
> For details of P-SEAMLDR SEAMCALLs, see Intel® Trust Domain CPU
> Architectural Extensions, Revision 343754-002, Chapter 2.3 "INSTRUCTION
> SET REFERENCE".
> 
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> Tested-by: Farrah Chen <farrah.chen@xxxxxxxxx>
> Link: https://cdrdv2.intel.com/v1/dl/getContent/733582 # [1]
> 

[...]

> + * Serialize P-SEAMLDR calls since the hardware only allows a single CPU to
> + * interact with P-SEAMLDR simultaneously.
> + */
> +static DEFINE_RAW_SPINLOCK(seamldr_lock);
> +
> +static __maybe_unused int seamldr_call(u64 fn, struct tdx_module_args *args)
> +{
> +	/*
> +	 * Serialize P-SEAMLDR calls and disable interrupts as the calls
> +	 * can be made from IRQ context.
> +	 */
> +	guard(raw_spinlock_irqsave)(&seamldr_lock);

Why do you need to disable IRQ?  A plain raw_spinlock should work with both
cases where seamldr_call() is called from IRQ disabled context and normal
task context? 

> +	return seamcall_prerr(fn, args);
> +}