linux-kernel - Re: [PATCH v3 02/18] nitro_enclaves: Define the PCI device interface

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Date:   Mon, 01 Jun 2020 12:53:13 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     "Paraschiv, Andra-Irina" <andraprs@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Anthony Liguori <aliguori@...zon.com>,
        Colm MacCarthaigh <colmmacc@...zon.com>,
        Bjoern Doebel <doebel@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Frank van der Linden <fllinden@...zon.com>,
        Alexander Graf <graf@...zon.de>,
        Martin Pohlack <mpohlack@...zon.de>,
        Matt Wilson <msw@...zon.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Balbir Singh <sblbir@...zon.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stewart Smith <trawets@...zon.com>,
        Uwe Dannowski <uwed@...zon.de>, kvm@...r.kernel.org,
        ne-devel-upstream@...zon.com
Subject: Re: [PATCH v3 02/18] nitro_enclaves: Define the PCI device interface

On Tue, 2020-05-26 at 20:01 +0300, Paraschiv, Andra-Irina wrote:
> 
> On 26/05/2020 09:44, Greg KH wrote:
> > On Tue, May 26, 2020 at 01:13:18AM +0300, Andra Paraschiv wrote:
> > > +struct enclave_get_slot_req {
> > > +	/* Context ID (CID) for the enclave vsock device. */
> > > +	u64 enclave_cid;
> > > +} __attribute__ ((__packed__));
> > 
> > Can you really "pack" a single member structure?
> > 
> > Anyway, we have better ways to specify this instead of the "raw"
> > __attribute__ option.  But first see if you really need any of
> > these, at
> > first glance, I do not think you do at all, and they can all be
> > removed.
> 
> There are a couple of data structures with more than one member and 
> multiple field sizes. And for the ones that are not, gathered as 
> feedback from previous rounds of review that should consider adding
> a 
> "flags" field in there for further extensibility.
> 
> I can modify to have "__packed" instead of the attribute callout.

I tend to prefer designing the protocol so that all the fields are
naturally aligned, which should avoid the need for the attribute. Is
it possible in this case ?

Cheers,
Ben.