netdev - RE: [PATCH net 1/1] hv_netvsc: Fix missed pagebuf entries in netvsc_dma

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Message-ID: <BYAPR21MB1688416185F59759D4CBB365D7D69@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Thu, 2 Feb 2023 19:24:24 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH net 1/1] hv_netvsc: Fix missed pagebuf entries in
 netvsc_dma_map/unmap()

From: Paolo Abeni <pabeni@...hat.com> Sent: Thursday, February 2, 2023 12:31 AM
> 
> On Thu, 2023-02-02 at 05:20 +0000, Michael Kelley (LINUX) wrote:
> > From: Jakub Kicinski <kuba@...nel.org> Sent: Wednesday, February 1, 2023 9:01 PM
> > >
> > > 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_dev,
> > > >  			  struct hv_netvsc_packet *packet,
> > > >  			  struct hv_page_buffer *pb)
> > > >  {
> > > > -	u32 page_count =  packet->cp_partial ?
> > > > -		packet->page_buf_cnt - packet->rmsg_pgcnt :
> > > > -		packet->page_buf_cnt;
> > > > +	u32 page_count = packet->page_buf_cnt;
> > > >  	dma_addr_t dma;
> > > >  	int i;
> > >
> > > Suspiciously, the caller still does:
> > >
> > >                 if (packet->cp_partial)
> > >                         pb += packet->rmsg_pgcnt;
> > >
> > >                 ret = netvsc_dma_map(ndev_ctx->device_ctx, packet, pb);
> > >
> > > Shouldn't that if () pb +=... also go away?
> >
> > No -- it's correct.
> >
> > 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.
> >
> > Haiyang -- any insight?
> 
> While at that, please also have a look at the following allocation in
> netvsc_dma_map():
> 
> 	packet->dma_range = 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.
> 

Thanks for pointing this out.  I've made a note to do a fix.

Michael