linux-kernel - Re: [PATCH 2/5] x86/sgx: Add kernel-doc descriptions for params passed to vDSO user handler

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Message-ID: <9adc3a5437cf7d9af99642a0df837bbd0237bb58.camel@intel.com>
Date: Thu, 13 Nov 2025 01:59:08 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "tglx@...utronix.de" <tglx@...utronix.de>, "x86@...nel.org"
	<x86@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>, "jarkko@...nel.org"
	<jarkko@...nel.org>, "seanjc@...gle.com" <seanjc@...gle.com>, "bp@...en8.de"
	<bp@...en8.de>, "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC: "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
	"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] x86/sgx: Add kernel-doc descriptions for params
 passed to vDSO user handler

On Wed, 2025-11-12 at 08:07 -0800, Sean Christopherson wrote:
> Add kernel-doc markup for the register parameters passed by the vDSO blob
> to the user handler to suppress build warnings, e.g.
> 
>   WARNING: arch/x86/include/uapi/asm/sgx.h:157 function parameter 'r8' not
>            described in 'sgx_enclave_user_handler_t'
> 
> Call out that except for RSP, the registers are undefined on asynchronous
> exits as far as the vDSO ABI is concerned.  E.g. the vDSO's exception
> handler clobbers RDX, RDI, and RSI, and the kernel doesn't guarantee that
> R8 or R9 will be zero (the synthetic value loaded by the CPU).

Perhaps a nit:

I am not that familiar with this part, but AFAICT the kernel always sets
RDI/RSI/RDX to exception vector/error code/addr before invoking the user
handler, after the vDSO's exception handler clobbers them.

Since you are adding description to them, should we somehow call this out in
the comment, if I didn't miss anything?

> 
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Closes: https://lore.kernel.org/all/20251106145506.145fc620@canb.auug.org.au
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/include/uapi/asm/sgx.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
> index a438ea43bfd1..0d408f001ac6 100644
> --- a/arch/x86/include/uapi/asm/sgx.h
> +++ b/arch/x86/include/uapi/asm/sgx.h
> @@ -143,6 +143,12 @@ struct sgx_enclave_run;
>  /**
>   * typedef sgx_enclave_user_handler_t - Exit handler function accepted by
>   *					__vdso_sgx_enter_enclave()
> + * @rdi:	RDI at the time of EEXIT, undefined on AEX
> + * @rsi:	RSI at the time of EEXIT, undefined on AEX
> + * @rdx:	RDX at the time of EEXIT, undefined on AEX
> + * @rsp:	RSP (untrusted) at the time of EEXIT or AEX
> + * @r8:		R8 at the time of EEXIT, undefined on AEX
> + * @r9:		R9 at the time of EEXIT, undefined on AEX
>   * @run:	The run instance given by the caller
>   *
>   * The register parameters contain the snapshot of their values at enclave