Re: [RFC PATCH 4/4] x86/vdso: x86/sgx: Allow the user to exit the vDSO loop on interrupts

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

On Mon, Aug 17, 2020 at 09:24:05PM -0700, Sean Christopherson wrote:
> Allow userspace to exit the vDSO on interrupts that are acknowledged
> while the enclave is active.  This allows the user's runtime to switch
> contexts at opportune times without additional overhead, e.g. when using
> an M:N threading model (where M user threads run N TCSs, with N > M).
> 
> Suggested-by: Jethro Beekman <jethro@fortanix.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/entry/vdso/vsgx_enter_enclave.S | 27 ++++++++++++++++++++----
>  arch/x86/include/uapi/asm/sgx.h          |  3 +++
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> index b09e87dbe9334..33428c0f94b0d 100644
> --- a/arch/x86/entry/vdso/vsgx_enter_enclave.S
> +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> @@ -21,6 +21,9 @@
>  
>  #define SGX_SYNCHRONOUS_EXIT	0
>  #define SGX_EXCEPTION_EXIT	1
> +#define SGX_INTERRUPT_EXIT	2
> +
> +#define SGX_EXIT_ON_INTERRUPTS	1

This naming scheme does not look too great.

I have nothing principal about code changes, *if* this is the approach
where we want to move. I did not look every detail because I'm not sure
what is the consensus yet.

/Jarkko