Re: [PATCH v5 04/22] x86/virt/seamldr: Introduce a wrapper for P-SEAMLDR SEAMCALLs

[Kiryl Shutsemau <kas@kernel.org>]

On Sun, Mar 15, 2026 at 06:58:24AM -0700, 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 need to interact with it for runtime update.
> 
> 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>
> Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
> Tested-by: Farrah Chen <farrah.chen@intel.com>
> Link: https://cdrdv2.intel.com/v1/dl/getContent/733582 # [1]
> ---
> v5:
>  - Don't save/restore irq flags as P-SEAMLDR calls are made only in process
>    context
>  - clarify why raw_spinlock is used [Dave]
> 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 | 24 ++++++++++++++++++++++++
>  2 files changed, 25 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..7ed9be89017c
> --- /dev/null
> +++ b/arch/x86/virt/vmx/tdx/seamldr.c
> @@ -0,0 +1,24 @@
> +// 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. Use raw version as the calls can
> + * be made with interrupts disabled.

Hm. I am not sure how it explains use of raw_spinlock. What's wrong with
using plain spinlock with interrupts disabled?

> + */
> +static DEFINE_RAW_SPINLOCK(seamldr_lock);
> +
> +static __maybe_unused int seamldr_call(u64 fn, struct tdx_module_args *args)
> +{
> +	guard(raw_spinlock)(&seamldr_lock);
> +	return seamcall_prerr(fn, args);
> +}
> -- 
> 2.47.3
> 

-- 
  Kiryl Shutsemau / Kirill A. Shutemov