Re: [PATCH] Drivers: hv: balloon: account for vmbus packet header in max_pkt_size

[Wei Liu <wei.liu@kernel.org>]

On Thu, Jan 20, 2022 at 04:20:52AM +0800, Yanming Liu wrote:
> Commit adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V
> out of the ring buffer") introduced a notion of maximum packet size in
> vmbus channel and used that size to initialize a buffer holding all
> incoming packet along with their vmbus packet header. hv_balloon uses
> the default maximum packet size VMBUS_DEFAULT_MAX_PKT_SIZE which matches
> its maximum message size, however vmbus_open expects this size to also
> include vmbus packet header. This leads to 4096 bytes
> dm_unballoon_request messages being truncated to 4080 bytes. When the
> driver tries to read next packet it starts from a wrong read_index,
> receives garbage and prints a lot of "Unhandled message: type:
> <garbage>" in dmesg.
> 
> Allocate the buffer with HV_HYP_PAGE_SIZE more bytes to make room for
> the header.
> 
> Fixes: adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V out of the ring buffer")
> Suggested-by: Michael Kelley (LINUX) <mikelley@microsoft.com>
> Suggested-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> Signed-off-by: Yanming Liu <yanminglr@gmail.com>

Applied to hyperv-fixes. Thanks.