Message-ID: <8a4d08f94d3e6fe8b6da68440eaa89a088ad84f9.camel@redhat.com>
Subject: Re: [PATCH net 1/1] hv_netvsc: Fix missed pagebuf entries in
 netvsc_dma_map/unmap()
From:   Paolo Abeni <pabeni@redhat.com>
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        Jakub Kicinski <kuba@kernel.org>
Cc:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Date:   Thu, 02 Feb 2023 09:30:45 +0100
In-Reply-To: <BYAPR21MB1688B7F47F9ADF2E40E9DEE4D7D69@BYAPR21MB1688.namprd21.prod.outlook.com>
References: <1675135986-254490-1-git-send-email-mikelley@microsoft.com>
         <20230201210107.450ff5d3@kernel.org>
         <BYAPR21MB1688B7F47F9ADF2E40E9DEE4D7D69@BYAPR21MB1688.namprd21.prod.outlook.com>
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On Thu, 2023-02-02 at 05:20 +0000, Michael Kelley (LINUX) wrote:
> From: Jakub Kicinski <kuba@kernel.org> Sent: Wednesday, February 1, 2023 =
9:01 PM
> >=20
> > On Mon, 30 Jan 2023 19:33:06 -0800 Michael Kelley wrote:
> > > @@ -990,9 +987,7 @@ static int netvsc_dma_map(struct hv_device *hv_de=
v,
> > >  			  struct hv_netvsc_packet *packet,
> > >  			  struct hv_page_buffer *pb)
> > >  {
> > > -	u32 page_count =3D  packet->cp_partial ?
> > > -		packet->page_buf_cnt - packet->rmsg_pgcnt :
> > > -		packet->page_buf_cnt;
> > > +	u32 page_count =3D packet->page_buf_cnt;
> > >  	dma_addr_t dma;
> > >  	int i;
> >=20
> > Suspiciously, the caller still does:
> >=20
> >                 if (packet->cp_partial)
> >                         pb +=3D packet->rmsg_pgcnt;
> >=20
> >                 ret =3D netvsc_dma_map(ndev_ctx->device_ctx, packet, pb=
);
> >=20
> > Shouldn't that if () pb +=3D... also go away?
>=20
> No -- it's correct.
>=20
> In netvsc_send(), cp_partial is tested and packet->page_buf_cnt is
> adjusted.  But the pointer into the pagebuf array is not adjusted in
> netvsc_send().  Instead it is adjusted here in netvsc_send_pkt(), which
> brings it back in sync with packet->page_buf_cnt.

Ok

> I don't know if there's a good reason for the adjustment being split
> across two different functions.  It doesn't seem like the most
> straightforward approach.  From a quick glance at the code it looks
> like this adjustment to 'pb' could move to netvsc_send() to be
> together with the adjustment to packet->page_buf_cnt,  but maybe
> there's a reason for the split that I'm not familiar with.
>=20
> Haiyang -- any insight?

While at that, please also have a look at the following allocation in
netvsc_dma_map():

	packet->dma_range =3D kcalloc(page_count,
                                    sizeof(*packet->dma_range),
                                    GFP_KERNEL);

which looks wrong - netvsc_dma_map() should be in atomic context.

Anyway it's a topic unrelated from this patch. I just stumbled upon it
while reviewing.

Cheers,

Paolo