netdev - Re: [net-next PATCH v9 1/8] octeontx2-pf: map skb data as device writeable

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Message-ID: <CAAeCc_nPP7FU7KUZoW+9AVPdaqTpVopEKQGVpzHgXkBUzfa1xQ@mail.gmail.com>
Date: Mon, 11 Nov 2024 10:31:02 +0530
From: Bharat Bhushan <bharatb.linux@...il.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: Bharat Bhushan <bbhushan2@...vell.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, sgoutham@...vell.com, gakula@...vell.com, 
	sbhatta@...vell.com, hkelam@...vell.com, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, jerinj@...vell.com, 
	lcherian@...vell.com, ndabilpuram@...vell.com, sd@...asysnail.net
Subject: Re: [net-next PATCH v9 1/8] octeontx2-pf: map skb data as device writeable

On Sun, Nov 10, 2024 at 7:53 PM Leon Romanovsky <leon@...nel.org> wrote:
>
> On Fri, Nov 08, 2024 at 10:27:01AM +0530, Bharat Bhushan wrote:
> > Crypto hardware need write permission for in-place encrypt
> > or decrypt operation on skb-data to support IPsec crypto
> > offload. That patch uses skb_unshare to make skb data writeable
> > for ipsec crypto offload and map skb fragment memory as
> > device read-write.
> >
> > Signed-off-by: Bharat Bhushan <bbhushan2@...vell.com>
> > ---
> > v7->v8:
> >  - spell correction (s/sdk/skb) in description
> >
> > v6->v7:
> >  - skb data was mapped as device writeable but it was not ensured
> >    that skb is writeable. This version calls skb_unshare() to make
> >    skb data writeable.
> >
> >  .../ethernet/marvell/octeontx2/nic/otx2_txrx.c | 18 ++++++++++++++++--
> >  1 file changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c
> > index 7aaf32e9aa95..49b6b091ba41 100644
> > --- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c
> > +++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c
> > @@ -11,6 +11,7 @@
> >  #include <linux/bpf.h>
> >  #include <linux/bpf_trace.h>
> >  #include <net/ip6_checksum.h>
> > +#include <net/xfrm.h>
> >
> >  #include "otx2_reg.h"
> >  #include "otx2_common.h"
> > @@ -83,10 +84,17 @@ static unsigned int frag_num(unsigned int i)
> >  static dma_addr_t otx2_dma_map_skb_frag(struct otx2_nic *pfvf,
> >                                       struct sk_buff *skb, int seg, int *len)
> >  {
> > +     enum dma_data_direction dir = DMA_TO_DEVICE;
> >       const skb_frag_t *frag;
> >       struct page *page;
> >       int offset;
> >
> > +     /* Crypto hardware need write permission for ipsec crypto offload */
> > +     if (unlikely(xfrm_offload(skb))) {
> > +             dir = DMA_BIDIRECTIONAL;
> > +             skb = skb_unshare(skb, GFP_ATOMIC);
> > +     }
> > +
> >       /* First segment is always skb->data */
> >       if (!seg) {
> >               page = virt_to_page(skb->data);
> > @@ -98,16 +106,22 @@ static dma_addr_t otx2_dma_map_skb_frag(struct otx2_nic *pfvf,
> >               offset = skb_frag_off(frag);
> >               *len = skb_frag_size(frag);
> >       }
> > -     return otx2_dma_map_page(pfvf, page, offset, *len, DMA_TO_DEVICE);
> > +     return otx2_dma_map_page(pfvf, page, offset, *len, dir);
>
> Did I read correctly and you perform DMA mapping on every SKB in data path?
> How bad does it perform if you enable IOMMU?

Yes Leon, currently DMA mapping is done with each SKB, That's true
even with non-ipsec cases.
Performance is not good with IOMMU enabled. Given the context of this
series, it just extends the same for ipsec use cases.

Thanks
-Bharat

>
> Thanks
>
> >  }
> >
> >  static void otx2_dma_unmap_skb_frags(struct otx2_nic *pfvf, struct sg_list *sg)
> >  {
> > +     enum dma_data_direction dir = DMA_TO_DEVICE;
> > +     struct sk_buff *skb = NULL;
> >       int seg;
> >
> > +     skb = (struct sk_buff *)sg->skb;
> > +     if (unlikely(xfrm_offload(skb)))
> > +             dir = DMA_BIDIRECTIONAL;
> > +
> >       for (seg = 0; seg < sg->num_segs; seg++) {
> >               otx2_dma_unmap_page(pfvf, sg->dma_addr[seg],
> > -                                 sg->size[seg], DMA_TO_DEVICE);
> > +                                 sg->size[seg], dir);
> >       }
> >       sg->num_segs = 0;
> >  }
> > --
> > 2.34.1
> >
> >
>