Re: [Qemu-devel] [PATCH 46/60] e1000: Discard oversized packets based on SBP|LPE

[Amos Kong <akong@redhat.com>]

On Wed, Nov 27, 2013 at 07:14:30PM +0800, Amos Kong wrote:
> On Mon, Feb 04, 2013 at 02:40:56PM +0400, Michael Tokarev wrote:
> > From: Michael Contreras <michael@inetric.com>
> > 
> > Discard packets longer than 16384 when !SBP to match the hardware behavior.
> > 
> > Signed-off-by: Michael Contreras <michael@inetric.com>
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > (cherry picked from commit 2c0331f4f7d241995452b99afaf0aab00493334a)
> > 
> > Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> > ---
> >  hw/e1000.c |    7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/e1000.c b/hw/e1000.c
> > index e22ba3d..87c798b 100644
> > --- a/hw/e1000.c
> > +++ b/hw/e1000.c
> > @@ -61,6 +61,8 @@ static int debugflags = DBGBIT(TXERR) | DBGBIT(GENERAL);
> >  
> >  /* this is the size past which hardware will drop packets when setting LPE=0 */
> >  #define MAXIMUM_ETHERNET_VLAN_SIZE 1522
> > +/* this is the size past which hardware will drop packets when setting LPE=1 */
> > +#define MAXIMUM_ETHERNET_LPE_SIZE 16384
> >  
> >  /*
> >   * HW models:
> > @@ -799,8 +801,9 @@ e1000_receive(VLANClientState *nc, const uint8_t *buf, size_t size)
> >      }
> >  
> >      /* Discard oversized packets if !LPE and !SBP. */
> > -    if (size > MAXIMUM_ETHERNET_VLAN_SIZE
> > -        && !(s->mac_reg[RCTL] & E1000_RCTL_LPE)
> > +    if ((size > MAXIMUM_ETHERNET_LPE_SIZE ||
> > +        (size > MAXIMUM_ETHERNET_VLAN_SIZE
> > +        && !(s->mac_reg[RCTL] & E1000_RCTL_LPE)))
> >          && !(s->mac_reg[RCTL] & E1000_RCTL_SBP)) {
> >          return size;
> 
> 
> This change is correct. I have a related question to ask.
> 
> I enabled E1000_DEBUG in qemu, and try to change nic MTU to >1500
> in Windows 7/ Windows 8 guest. I found RCTL register isn't changed.
> 
> It mean E1000_RCTL_LPE bit is 0, so I ping guest from host with >
> 1500 size packet, the request ICMP packets will be dropped.
> 
> It seems a e1000 driver bug of Windows?
 
In e1000 driver of Windows, there is a "Jumbo Packet" option, it's
used to enable LPE, after enabled Jumbo packet, I can ping guest with
large packet (>1500)