Re: [RFC PATCH 2/4] x86/vdso: x86/sgx: Rework __vdso_sgx_enter_enclave() API

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Mon, Aug 17, 2020 at 09:24:03PM -0700, Sean Christopherson wrote:
> Rework __vdso_sgx_enter_enclave() to use a struct to hold the input and
> output params.  In the new struct, add an opaque "user_data" that can be
> used to pass context across the vDSO, and an explicit "exit_reason" to
> avoid overloading the return value.
> 
> Moving the params into a struct will also make it less painful to use
> dedicated exit reasons, and to support exiting on interrupts in future
> patches.
> 
> Cc: Nathaniel McCallum <npmccallum@redhat.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/entry/vdso/vsgx_enter_enclave.S | 72 ++++++++++++-------
>  arch/x86/include/uapi/asm/sgx.h          | 90 ++++++++++++++++--------
>  2 files changed, 107 insertions(+), 55 deletions(-)
> 
> diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> index 2d88acd408d4e..aaae6d6e28ac3 100644
> --- a/arch/x86/entry/vdso/vsgx_enter_enclave.S
> +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> @@ -7,9 +7,21 @@
>  
>  #include "extable.h"
>  
> -#define EX_LEAF		0*8
> -#define EX_TRAPNR	0*8+4
> -#define EX_ERROR_CODE	0*8+6
> +/* Offset of 'struct sgx_enter_enclave' relative to %rbp. */
> +#define RUN_OFFSET	2*8

Some better name please.

> +
> +/* Offsets into 'struct sgx_enter_enclave'. */
> +#define TCS_OFFEST		0*8
> +#define FLAGS_OFFSET		1*8
> +#define EXIT_LEAF_OFFSET	2*8
> +#define EXIT_REASON_OFFSET	2*8 + 4
> +#define USER_HANDLER_OFFSET	3*8
> +/* #define USER_DATA_OFFSET	4*8 */
> +#define EXCEPTION_OFFSET	5*8

These non-prefixed constants make the code really stressing to read
given the complexity of it. Please, just write them like
SGX_ENTER_ENCLAVE_TCS and so forth.

/Jarkko