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

[Binbin Wu <binbin.wu@linux.intel.com>]

On 2/12/2026 10:35 PM, 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.
> 
> 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@intel.com>
> Tested-by: Farrah Chen <farrah.chen@intel.com>
> Link: https://cdrdv2.intel.com/v1/dl/getContent/733582 # [1]

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>

> ---
> v4:
>  - Give more background about P-SEAMLDR in changelog [Dave]
>  - Don't handle P-SEAMLDR's "no_entropy" error [Dave]
>  - Assume current VMCS is preserved across P-SEAMLDR calls [Dave]
>  - I'm not adding Reviewed-by tags as the code has changed significantly.
> v2:
>  - don't create a new, inferior framework to save/restore VMCS
>  - use human-friendly language, just "current VMCS" rather than
>    SDM term "current-VMCS pointer"
>  - don't mix guard() with goto
> ---
>  arch/x86/virt/vmx/tdx/Makefile  |  2 +-
>  arch/x86/virt/vmx/tdx/seamldr.c | 27 +++++++++++++++++++++++++++
>  2 files changed, 28 insertions(+), 1 deletion(-)
>  create mode 100644 arch/x86/virt/vmx/tdx/seamldr.c
> 
> diff --git a/arch/x86/virt/vmx/tdx/Makefile b/arch/x86/virt/vmx/tdx/Makefile
> index 90da47eb85ee..d1dbc5cc5697 100644
> --- a/arch/x86/virt/vmx/tdx/Makefile
> +++ b/arch/x86/virt/vmx/tdx/Makefile
> @@ -1,2 +1,2 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> -obj-y += seamcall.o tdx.o
> +obj-y += seamcall.o seamldr.o tdx.o
> diff --git a/arch/x86/virt/vmx/tdx/seamldr.c b/arch/x86/virt/vmx/tdx/seamldr.c
> new file mode 100644
> index 000000000000..fb59b3e2aa37
> --- /dev/null
> +++ b/arch/x86/virt/vmx/tdx/seamldr.c
> @@ -0,0 +1,27 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * P-SEAMLDR support for TDX Module management features like runtime updates
> + *
> + * Copyright (C) 2025 Intel Corporation
> + */
> +#define pr_fmt(fmt)	"seamldr: " fmt
> +
> +#include <linux/spinlock.h>
> +
> +#include "seamcall_internal.h"
> +
> +/*
> + * 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);
> +	return seamcall_prerr(fn, args);
> +}