linux-kernel - RE: [PATCH 1/1] Drivers: hv: vmbus: Support a vmbus API for efficiently sending page arrays

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Message-ID: <BY2PR0301MB0711EE39793F0016994F6230A06F0@BY2PR0301MB0711.namprd03.prod.outlook.com>
Date:	Mon, 15 Dec 2014 19:52:36 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>
Subject: RE: [PATCH 1/1] Drivers: hv: vmbus: Support a vmbus API for
 efficiently sending page arrays



> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> Sent: Monday, December 15, 2014 11:34 AM
> To: KY Srinivasan
> Cc: linux-kernel@...r.kernel.org; devel@...uxdriverproject.org;
> olaf@...fle.de; apw@...onical.com; jasowang@...hat.com
> Subject: Re: [PATCH 1/1] Drivers: hv: vmbus: Support a vmbus API for
> efficiently sending page arrays
> 
> On Mon, Dec 15, 2014 at 12:33:47PM -0800, K. Y. Srinivasan wrote:
> > Currently, the API for sending a multi-page buffer over VMBUS is
> > limited to a maximum pfn array of MAX_MULTIPAGE_BUFFER_COUNT.
> This
> > limitation is not imposed by the host and unnecessarily limits the
> > maximum payload that can be sent. Implement an API that does not have
> this restriction.
> >
> > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> > ---
> >  drivers/hv/channel.c   |   44
> ++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/hyperv.h |   31 +++++++++++++++++++++++++++++++
> >  2 files changed, 75 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c index
> > c76ffbe..18c4f23 100644
> > --- a/drivers/hv/channel.c
> > +++ b/drivers/hv/channel.c
> > @@ -686,6 +686,50 @@
> EXPORT_SYMBOL_GPL(vmbus_sendpacket_pagebuffer);
> >  /*
> >   * vmbus_sendpacket_multipagebuffer - Send a multi-page buffer packet
> >   * using a GPADL Direct packet type.
> > + * The buffer includes the vmbus descriptor.
> > + */
> > +int vmbus_sendpacket_mpb_desc(struct vmbus_channel *channel,
> > +			      struct vmbus_packet_mpb_array *desc,
> > +			      u32 desc_size,
> > +			      void *buffer, u32 bufferlen, u64 requestid) {
> > +	int ret;
> > +	u32 packetlen;
> > +	u32 packetlen_aligned;
> > +	struct kvec bufferlist[3];
> > +	u64 aligned_data = 0;
> > +	bool signal = false;
> > +
> > +	packetlen = desc_size + bufferlen;
> > +	packetlen_aligned = ALIGN(packetlen, sizeof(u64));
> > +
> > +	/* Setup the descriptor */
> > +	desc->type = VM_PKT_DATA_USING_GPA_DIRECT;
> > +	desc->flags =
> VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED;
> > +	desc->dataoffset8 = desc_size >> 3; /* in 8-bytes grandularity */
> > +	desc->length8 = (u16)(packetlen_aligned >> 3);
> > +	desc->transactionid = requestid;
> > +	desc->rangecount = 1;
> > +
> > +	bufferlist[0].iov_base = desc;
> > +	bufferlist[0].iov_len = desc_size;
> > +	bufferlist[1].iov_base = buffer;
> > +	bufferlist[1].iov_len = bufferlen;
> > +	bufferlist[2].iov_base = &aligned_data;
> > +	bufferlist[2].iov_len = (packetlen_aligned - packetlen);
> > +
> > +	ret = hv_ringbuffer_write(&channel->outbound, bufferlist, 3,
> > +&signal);
> > +
> > +	if (ret == 0 && signal)
> > +		vmbus_setevent(channel);
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(vmbus_sendpacket_mpb_desc);
> > +
> > +/*
> > + * vmbus_sendpacket_multipagebuffer - Send a multi-page buffer packet
> > + * using a GPADL Direct packet type.
> >   */
> >  int vmbus_sendpacket_multipagebuffer(struct vmbus_channel *channel,
> >  				struct hv_multipage_buffer
> *multi_pagebuffer, diff --git
> > a/include/linux/hyperv.h b/include/linux/hyperv.h index
> > 08cfaff..8615b0d 100644
> > --- a/include/linux/hyperv.h
> > +++ b/include/linux/hyperv.h
> > @@ -57,6 +57,18 @@ struct hv_multipage_buffer {
> >  	u64 pfn_array[MAX_MULTIPAGE_BUFFER_COUNT];
> >  };
> >
> > +/*
> > + * Multiple-page buffer array; the pfn array is variable size:
> > + * The number of entries in the PFN array is determined by
> > + * "len" and "offset".
> > + */
> > +struct hv_mpb_array {
> > +	/* Length and Offset determines the # of pfns in the array */
> > +	u32 len;
> > +	u32 offset;
> > +	u64 pfn_array[];
> > +};
> 
> Does this cross the user/kernel boundry?  If so, they need to be __u32 and
> __u64 variables.

This does not cross user/kernel boundry. 
> 
> > +
> >  /* 0x18 includes the proprietary packet header */
> >  #define MAX_PAGE_BUFFER_PACKET		(0x18 +
> 	\
> >  					(sizeof(struct hv_page_buffer) * \
> @@ -812,6 +824,18 @@ struct
> > vmbus_channel_packet_multipage_buffer {
> >  	struct hv_multipage_buffer range;
> >  } __packed;
> >
> > +/* The format must be the same as struct vmdata_gpa_direct */ struct
> > +vmbus_packet_mpb_array {
> > +	u16 type;
> > +	u16 dataoffset8;
> > +	u16 length8;
> > +	u16 flags;
> > +	u64 transactionid;
> > +	u32 reserved;
> > +	u32 rangecount;         /* Always 1 in this case */
> > +	struct hv_mpb_array range;
> > +} __packed;
> 
> Same here.
This is completely internal to the kernel.

Regards,

K. Y
> 
> thanks,
> 
> greg k-h
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