linux-kernel - Re: [PATCH v8 2/2] x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node

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Message-ID: <4c3e7a41c545d10ed4aabcfa08118b1e2f80e3fd.camel@kernel.org>
Date:   Tue, 26 Oct 2021 02:46:20 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        reinette.chatre@...el.com, tony.luck@...el.com,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org
Subject: Re: [PATCH v8 2/2] x86/sgx: Add an attribute for the amount of SGX
 memory in a NUMA node

On Mon, 2021-10-25 at 07:15 +0200, Greg Kroah-Hartman wrote:
> On Sun, Oct 24, 2021 at 05:24:43PM +0300, Jarkko Sakkinen wrote:
> > On Sat, 2021-10-23 at 08:33 +0200, Greg Kroah-Hartman wrote:
> > > On Sat, Oct 23, 2021 at 04:02:48AM +0300, Jarkko Sakkinen wrote:
> > > > On Mon, 2021-10-18 at 16:35 +0200, Greg Kroah-Hartman wrote:
> > > > > > +               ret = sysfs_create_group(&dev->kobj, &sgx_node_attr_group);
> > > > > 
> > > > > A huge hint, if a driver has to call a sysfs_* call, something is wrong.
> > > > > 
> > > > > Something is wrong here.
> > > > > 
> > > > > Why are you messing around with a kobject?  This is a device, that you
> > > > > control, you can just set the default attribute group for it and then
> > > > > the driver core will add and remove the sysfs group at the proper time,
> > > > > in the proper way.  Right now you are racing userspace and loosing.
> > > > > 
> > > > > Use the default group list, that is what it is there for.
> > > > 
> > > > I used sysfs_create_group() because node_devices is not owned by SGX
> > > > code. It is managed in drivers/base/node.c, and also initialized before
> > > > SGX.
> > > 
> > > Then that is broken, please do not use that device as your code does not
> > > "own" it.  Or fix the logic to be initialized earlier.
> > 
> > To get a synchronous initialization, I'd need to add the attributes as
> > part of this declaration:
> > 
> > static struct attribute *node_dev_attrs[] = {
> >         &dev_attr_cpumap.attr,
> >         &dev_attr_cpulist.attr,
> >         &dev_attr_meminfo.attr,
> >         &dev_attr_numastat.attr,
> >         &dev_attr_distance.attr,
> >         &dev_attr_vmstat.attr,
> >         NULL
> > };
> > ATTRIBUTE_GROUPS(node_dev);
> > 
> > That guarantees that the attribute exists at the time when the
> > node is created, e.g. in that sense this will fix the race with
> > uevent code.
> > 
> > However, up until sgx_init() has been completed, the attribute
> > will emit '0'.
> 
> Is that a problem?  Who would be wanting to use sgx until that happens?
> You have this issue today anyway, right?

Yeah, I guess I can just document this (as part of sysfs abi documentation).

Thank you for the feedback.

/Jarkko