netdev - Re: [net-next V5 PATCH 1/5] bpf: introduce new bpf cpu map type BPF_MAP_TYPE

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Message-ID: <20171009195924.662f1586@redhat.com>
Date:   Mon, 9 Oct 2017 19:59:24 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org, jakub.kicinski@...ronome.com,
        "Michael S. Tsirkin" <mst@...hat.com>, pavel.odintsov@...il.com,
        Jason Wang <jasowang@...hat.com>, mchan@...adcom.com,
        John Fastabend <john.fastabend@...il.com>,
        peter.waskiewicz.jr@...el.com,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>, brouer@...hat.com
Subject: Re: [net-next V5 PATCH 1/5] bpf: introduce new bpf cpu map type
 BPF_MAP_TYPE_CPUMAP

On Mon, 09 Oct 2017 15:31:21 +0200
Daniel Borkmann <daniel@...earbox.net> wrote:

> On 10/06/2017 06:12 PM, Jesper Dangaard Brouer wrote:
> [...]
> > +static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
> > +{
> > +	struct bpf_cpu_map *cmap;
> > +	int err = -ENOMEM;  
> 
> err init here is basically not needed since overriden later anyway
> w/o being read, but ...

Thank you for catching this! Guess, I'll send a V6 tomorrow.

[...]
> > +	/* Notice returns -EPERM on if map size is larger than memlock limit */
> > +	err = bpf_map_precharge_memlock(cmap->map.pages);
> > +	if (err)
> > +		goto free_cmap;  
> 
> ... here, you need to set err = -ENOMEM.

Yes, I see my mistake of assigning "err" here.

[...]
> > +static void *cpu_map_lookup_elem(struct bpf_map *map, void *key)
> > +{
> > +	struct bpf_cpu_map_entry *rcpu =
> > +		__cpu_map_lookup_elem(map, *(u32 *)key);
> > +
> > +	return rcpu ? &rcpu->qsize : NULL;  
> 
> I still think from my prior email/comment that we should use per-cpu
> scratch buffer here. Would be nice to keep the guarantee that noone
> can modify it, it's just a tiny change.

Well, it's no-longer really needed, right(?), as this patchset update,
change that bpf-side cannot invoke this.  The userspace-side reading
this will get a copy.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer