linux-kernel - Re: [PATCH v3 08/11] Input: hyperv-keyboard: Make ringbuffer at least take two pages

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Message-ID: <20200914084600.GA45838@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net>
Date:   Mon, 14 Sep 2020 16:46:00 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-hyperv@...r.kernel.org, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Michael Kelley <mikelley@...rosoft.com>, will@...nel.org,
        ardb@...nel.org, arnd@...db.de, catalin.marinas@....com,
        mark.rutland@....com, maz@...nel.org
Subject: Re: [PATCH v3 08/11] Input: hyperv-keyboard: Make ringbuffer at
 least take two pages

On Thu, Sep 10, 2020 at 10:34:52PM +0800, Boqun Feng wrote:
> When PAGE_SIZE > HV_HYP_PAGE_SIZE, we need the ringbuffer size to be at
> least 2 * PAGE_SIZE: one page for the header and at least one page of
> the data part (because of the alignment requirement for double mapping).
> 
> So make sure the ringbuffer sizes to be at least 2 * PAGE_SIZE when
> using vmbus_open() to establish the vmbus connection.
> 
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> ---
>  drivers/input/serio/hyperv-keyboard.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/serio/hyperv-keyboard.c b/drivers/input/serio/hyperv-keyboard.c
> index df4e9f6f4529..6ebc61e2db3f 100644
> --- a/drivers/input/serio/hyperv-keyboard.c
> +++ b/drivers/input/serio/hyperv-keyboard.c
> @@ -75,8 +75,8 @@ struct synth_kbd_keystroke {
>  
>  #define HK_MAXIMUM_MESSAGE_SIZE 256
>  
> -#define KBD_VSC_SEND_RING_BUFFER_SIZE		(40 * 1024)
> -#define KBD_VSC_RECV_RING_BUFFER_SIZE		(40 * 1024)
> +#define KBD_VSC_SEND_RING_BUFFER_SIZE	max(40 * 1024, (int)(2 * PAGE_SIZE))
> +#define KBD_VSC_RECV_RING_BUFFER_SIZE	max(40 * 1024, (int)(2 * PAGE_SIZE))
>  

Hmm.. just realized there is a problem here, if PAGE_SIZE = 16k, then
40 * 1024 > 2 * PAGE_SIZE, however in the ring buffer size should also
be page aligned, otherwise vmbus_open() will fail.

I plan to modify this as

in linux/hyperv.h:

#define VMBUS_RING_SIZE(payload_sz) PAGE_ALIGN(sizeof(struct hv_ring_buffer) + (playload_sz))

and here:

#define KBD_VSC_SEND_RING_BUFFER_SIZE VMBUS_RING_SIZE(36 * 1024)
#define KBD_VSC_RECV_RING_BUFFER_SIZE VMBUS_RING_SIZE(36 * 1024)

and the similar change for patch #9.

Thoughts?

Regards,
Boqun

>  #define XTKBD_EMUL0     0xe0
>  #define XTKBD_EMUL1     0xe1
> -- 
> 2.28.0
>