Messages in this thread | | | From | Jesper Dangaard Brouer <> | Date | Mon, 15 May 2023 18:17:02 +0200 | Subject | Re: [PATCH RESEND bpf-next 14/15] net, xdp: allow metadata > 32 |
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On 12/05/2023 17.26, Larysa Zaremba wrote: > From: Aleksander Lobakin <aleksander.lobakin@intel.com> > > When using XDP hints, metadata sometimes has to be much bigger > than 32 bytes. Relax the restriction, allow metadata larger than 32 bytes > and make __skb_metadata_differs() work with bigger lengths. > > Now size of metadata is only limited by the fact it is stored as u8 > in skb_shared_info, so maximum possible value is 255.
I'm confused, IIRC the metadata area isn't stored "in skb_shared_info". The maximum possible size is limited by the XDP headroom, which is also shared/limited with/by xdp_frame. I must be reading the sentence wrong, somehow.
> Other important > conditions, such as having enough space for xdp_frame building, are already > checked in bpf_xdp_adjust_meta(). > > The requirement of having its length aligned to 4 bytes is still > valid. > > Signed-off-by: Aleksander Lobakin <aleksander.lobakin@intel.com> > Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com> > --- > include/linux/skbuff.h | 13 ++++++++----- > include/net/xdp.h | 7 ++++++- > 2 files changed, 14 insertions(+), 6 deletions(-) > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > index 8ddb4af1a501..afcd372aecdf 100644 > --- a/include/linux/skbuff.h > +++ b/include/linux/skbuff.h > @@ -4219,10 +4219,13 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a, > { > const void *a = skb_metadata_end(skb_a); > const void *b = skb_metadata_end(skb_b); > - /* Using more efficient varaiant than plain call to memcmp(). */ > -#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64 > u64 diffs = 0; > > + if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) || > + BITS_PER_LONG != 64) > + goto slow; > + > + /* Using more efficient variant than plain call to memcmp(). */ > switch (meta_len) { > #define __it(x, op) (x -= sizeof(u##op)) > #define __it_diff(a, b, op) (*(u##op *)__it(a, op)) ^ (*(u##op *)__it(b, op)) > @@ -4242,11 +4245,11 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a, > fallthrough; > case 4: diffs |= __it_diff(a, b, 32); > break; > + default: > +slow: > + return memcmp(a - meta_len, b - meta_len, meta_len); > } > return diffs; > -#else > - return memcmp(a - meta_len, b - meta_len, meta_len); > -#endif > } > > static inline bool skb_metadata_differs(const struct sk_buff *skb_a, > diff --git a/include/net/xdp.h b/include/net/xdp.h > index 0fbd25616241..f48723250c7c 100644 > --- a/include/net/xdp.h > +++ b/include/net/xdp.h > @@ -370,7 +370,12 @@ xdp_data_meta_unsupported(const struct xdp_buff *xdp) > > static inline bool xdp_metalen_invalid(unsigned long metalen) > { > - return (metalen & (sizeof(__u32) - 1)) || (metalen > 32); > + typeof(metalen) meta_max; > + > + meta_max = type_max(typeof_member(struct skb_shared_info, meta_len)); > + BUILD_BUG_ON(!__builtin_constant_p(meta_max)); > + > + return !IS_ALIGNED(metalen, sizeof(u32)) || metalen > meta_max; > } > > struct xdp_attachment_info {
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