From: Stefan Hajnoczi <stefanha@gmail.com>
To: Dmitry Fleytman <dmitry@daynix.com>
Cc: Yan Vugenfirer <yan@daynix.com>,
Chris Webb <chris.webb@elastichosts.com>,
qemu-devel@nongnu.org,
Richard Davies <richard.davies@elastichosts.com>
Subject: Re: [Qemu-devel] [PATCH 1/2] Ignore RX tail kicks when RX disabled.
Date: Thu, 18 Oct 2012 10:09:09 +0200 [thread overview]
Message-ID: <20121018080909.GF22425@stefanha-thinkpad.redhat.com> (raw)
In-Reply-To: <1350498707-6749-2-git-send-email-dmitry@daynix.com>
On Wed, Oct 17, 2012 at 08:31:46PM +0200, Dmitry Fleytman wrote:
> Device RX initization from driver's side consists of following steps:
> 1. Initialize head and tail of RX ring to 0
> 2. Enable Rx (set bit in RCTL register)
> 3. Allocate buffers, fill descriptors
> 4. Write ring tail
>
> Forth operation signals hardware that RX buffers available
> and it may start packets indication.
>
> Current implementation treats first operation (write 0 to ring tail)
> as signal of buffers availability and starts data transfers as soon
> as RX enable indicaton arrives.
>
> This is not correct because there is a chance that ring is still
> empty (third action not performed yet) and then memory corruption
> occures.
Any idea what the point of hw/e1000.c check_rxov is? I see nothing in
the datasheet that requires these semantics.
The Linux e1000 driver never enables the RXO (rx fifo overflow)
interrupt, only RXDMT0 (receive descriptor minimum threshold). This
means hw/e1000.c will not upset the Linux e1000 driver when
e1000_receive() gets called with check_rxov == 1 and RDH == RDT == 0.
BTW the Linux e1000 driver does not follow the sequence recommended in
the datasheet 14.4 Receive Initialization, which would avoid the weird
window of time where RDH == RDT == 0.
If we get rid of check_rxov and always check rxbuf space then we have
the correct behavior. I'm a little nervous of simply dropping it
because its purpose is unclear to me :(.
Stefan
next prev parent reply other threads:[~2012-10-18 8:09 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-17 18:31 [Qemu-devel] [PATCH 0/2] E1000 RX/Live migration bugs fixed Dmitry Fleytman
2012-10-17 18:31 ` [Qemu-devel] [PATCH 1/2] Ignore RX tail kicks when RX disabled Dmitry Fleytman
2012-10-18 7:31 ` Stefan Hajnoczi
2012-10-18 8:08 ` Dmitry Fleytman
2012-10-18 8:09 ` Stefan Hajnoczi [this message]
2012-10-18 8:34 ` Dmitry Fleytman
2012-10-18 14:31 ` Stefan Hajnoczi
2012-10-18 16:06 ` Alexander Duyck
2012-10-18 16:12 ` Dmitry Fleytman
2012-10-17 18:31 ` [Qemu-devel] [PATCH 2/2] Add check_rxov into VMState Dmitry Fleytman
2012-10-18 7:24 ` Stefan Hajnoczi
2012-10-18 8:06 ` Dmitry Fleytman
2012-10-18 14:56 ` Avi Kivity
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