linux-kernel - Re: [PATCH] hv_utils: Set the maximum packet size for VSS driver to the length of the receive buffer

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Message-ID: <20210825190217.qh2c6yq5qr3ntum5@liuwe-devbox-debian-v2>
Date:   Wed, 25 Aug 2021 19:02:17 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     vkuznets <vkuznets@...hat.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Andres Beltran <lkmlabelt@...il.com>,
        "Andrea Parri (Microsoft)" <parri.andrea@...il.com>,
        Dexuan Cui <decui@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hv_utils: Set the maximum packet size for VSS driver to
 the length of the receive buffer

On Wed, Aug 25, 2021 at 06:33:10PM +0000, Michael Kelley wrote:
> From: Vitaly Kuznetsov <vkuznets@...hat.com> Sent: Wednesday, August 25, 2021 6:39 AM
> > 
> > Commit adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V out
> > of the ring buffer") introduced a notion of maximum packet size and for
> > KVM and FCOPY drivers set it to the length of the receive buffer. VSS
> > driver wasn't updated, this means that the maximum packet size is now
> > VMBUS_DEFAULT_MAX_PKT_SIZE (4k). Apparently, this is not enough. I'm
> > observing a packet of 6304 bytes which is being truncated to 4096. When
> > VSS driver tries to read next packet from ring buffer it starts from the
> > wrong offset and receives garbage.
> > 
> > Set the maximum packet size to 'HV_HYP_PAGE_SIZE * 2' in VSS driver. This
> > matches the length of the receive buffer and is in line with other utils
> > drivers.
> > 
> > Fixes: adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V out of the ring buffer")
> > Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
[...]
> 
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>

Given we're really close to the merge window I'm going to apply this to
hyperv-next.

Wei.