Re: [RFC PATCH v3 08/27] x86/sgx: Initialize virtual EPC driver even when SGX driver is disabled

Kai Huang
2021-02-02T00:13:02Z

On Mon, 1 Feb 2021 09:23:18 -0800 Sean Christopherson wrote:
> On Mon, Feb 01, 2021, Dave Hansen wrote:
> > On 1/31/21 9:40 PM, Kai Huang wrote:
> > >>> - ret = sgx_drv_init();
> > >>> + /* Success if the native *or* virtual EPC driver initialized cleanly. */
> > >>> + ret = !!sgx_drv_init() & !!sgx_vepc_init();
> > >> If would create more dumb code and just add
> > >>
> > >> ret = sgx_vepc_init()
> > >> if (ret)
> > >> goto err_kthread;
> >
> > Jarkko, I'm not sure I understand this suggestion.
> >
> > > Do you mean you want below?
> > >
> > > ret = sgx_drv_init();
> > > ret = sgx_vepc_init();
> > > if (ret)
> > > goto err_kthread;
> > >
> > > This was Sean's original code, but Dave didn't like it.
>
> The problem is it's wrong. That snippet would incorrectly bail if drv_init()
> succeeds but vepc_init() fails.
>
> The alternative to the bitwise AND is to snapshot the result in two separate
> variables:
>
> ret = sgx_drv_init();
> ret2 = sgx_vepc_init();
> if (ret && ret2)
> goto err_kthread;
>
> or check the return from drv_init() _after_ vepc_init():
>
> ret = sgx_drv_init();
> if (sgx_vepc_init() && ret)
> goto err_kthread;
>
>
> As evidenced by this thread, the behavior is subtle and easy to get wrong. I
> deliberately chose the option that was the weirdest specifically to reduce the
> probability of someone incorrectly "cleaning up" the code.
>
> > Are you sure? I remember the !!&!! abomination being Sean's doing. :)
>
> Yep! That 100% functionally correct horror is my doing.
>
> > > Sean/Dave,
> > >
> > > Please let me know which way you prefer.
> >
> > Kai, I don't really know you are saying here. In the end,
> > sgx_vepc_init() has to run regardless of whether sgx_drv_init() is
> > successful or not. Also, we only want to 'goto err_kthraed' if *BOTH*
> > fail. The code you have above will, for instance, 'goto err_kthread' if
> > sgx_drv_init() succeeds but sgx_vepc_init() fails. It entirely
> > disregards the sgx_drv_init() error code.
>

Hi Dave, Sean,

Yeah sorry my bad. The example I provided won't work. So I'd like keep the !!
&!! :)

Thanks.

Jarkko, please let us know if you still have concern.