linux-kernel - Re: [PATCH v3 07/25] x86/sgx: Initialize virtual EPC driver even when SGX driver is disabled

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Date:   Fri, 2 Apr 2021 19:30:23 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Kai Huang <kai.huang@...el.com>, kvm@...r.kernel.org,
        linux-sgx@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, jarkko@...nel.org, luto@...nel.org,
        dave.hansen@...el.com, rick.p.edgecombe@...el.com,
        haitao.huang@...el.com, pbonzini@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH v3 07/25] x86/sgx: Initialize virtual EPC driver even
 when SGX driver is disabled

On Fri, Apr 02, 2021, Borislav Petkov wrote:
> On Fri, Apr 02, 2021 at 03:42:51PM +0000, Sean Christopherson wrote:
> > Nope!  That's wrong, as sgx_epc_init() will not be called if sgx_drv_init()
> > succeeds.  And writing it as "if (sgx_drv_init() || sgx_vepc_init())" is also
> > wrong since that would kill SGX when one of the drivers is alive and well.
> 
> Bah, right you are.
> 
> How about:
> 
> 	/* Error out only if both fail to initialize. */
>         ret = sgx_drv_init();
> 
>         if (sgx_vepc_init() && ret)
>                 goto err_kthread;

Heh, that's what I had originally and used for literally years.  IIRC, I
suggested the "!! & !!" abomination after internal review complained about the
oddness of the above.

FWIW, I think the above is far less likely to be misread, even though I love the
cleverness of the bitwise AND.

> 
> And yah, this looks strange so it needs the comment to explain what's
> going on here.
> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette