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From: Boqun Feng <boqun.feng@gmail.com>
To: Michael Kelley <mikelley@microsoft.com>
Cc: "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Jiri Kosina <jikos@kernel.org>,
	Benjamin Tissoires <benjamin.tissoires@redhat.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>
Subject: Re: [RFC 03/11] Drivers: hv: vmbus: Introduce types of GPADL
Date: Thu, 23 Jul 2020 07:43:21 +0800
Message-ID: <20200722234321.GC35358@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> (raw)
In-Reply-To: <MW2PR2101MB1052E3D15D411A5DC62A60F2D7790@MW2PR2101MB1052.namprd21.prod.outlook.com>

On Wed, Jul 22, 2020 at 11:25:18PM +0000, Michael Kelley wrote:
> From: Boqun Feng <boqun.feng@gmail.com> Sent: Monday, July 20, 2020 6:41 PM
> > 
> > This patch introduces two types of GPADL: HV_GPADL_{BUFFER, RING}. The
> > types of GPADL are purely the concept in the guest, IOW the hypervisor
> > treat them as the same.
> > 
> > The reason of introducing the types of GPADL is to support guests whose
> > page size is not 4k (the page size of Hyper-V hypervisor). In these
> > guests, both the headers and the data parts of the ringbuffers need to
> > be aligned to the PAGE_SIZE, because 1) some of the ringbuffers will be
> > mapped into userspace and 2) we use "double mapping" mechanism to
> > support fast wrap-around, and "double mapping" relies on ringbuffers
> > being page-aligned. However, the Hyper-V hypervisor only uses 4k
> > (HV_HYP_PAGE_SIZE) headers. Our solution to this is that we always make
> > the headers of ringbuffers take one guest page and when GPADL is
> > established between the guest and hypervisor, the only first 4k of
> > header is used. To handle this special case, we need the types of GPADL
> > to differ different guest memory usage for GPADL.
> > 
> > Type enum is introduced along with several general interfaces to
> > describe the differences between normal buffer GPADL and ringbuffer
> > GPADL.
> > 
> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > ---
> >  drivers/hv/channel.c   | 140 +++++++++++++++++++++++++++++++++++------
> >  include/linux/hyperv.h |  44 ++++++++++++-
> >  2 files changed, 164 insertions(+), 20 deletions(-)
> 
> [snip]
> 
> > 
> > 
> > @@ -437,7 +528,17 @@ static int __vmbus_open(struct vmbus_channel *newchannel,
> >  	open_msg->openid = newchannel->offermsg.child_relid;
> >  	open_msg->child_relid = newchannel->offermsg.child_relid;
> >  	open_msg->ringbuffer_gpadlhandle = newchannel->ringbuffer_gpadlhandle;
> > -	open_msg->downstream_ringbuffer_pageoffset = newchannel-
> > >ringbuffer_send_offset;
> > +	/*
> > +	 * The unit of ->downstream_ringbuffer_pageoffset is HV_HYP_PAGE and
> > +	 * the unit of ->ringbuffer_send_offset is PAGE, so here we first
> > +	 * calculate it into bytes and then convert into HV_HYP_PAGE. Also
> > +	 * ->ringbuffer_send_offset is the offset in guest, while
> > +	 * ->downstream_ringbuffer_pageoffset is the offset in gpadl (i.e. in
> > +	 * hypervisor), so a (PAGE_SIZE - HV_HYP_PAGE_SIZE) gap need to be
> > +	 * skipped.
> > +	 */
> > +	open_msg->downstream_ringbuffer_pageoffset =
> > +		((newchannel->ringbuffer_send_offset << PAGE_SHIFT) - (PAGE_SIZE -
> > HV_HYP_PAGE_SIZE)) >> HV_HYP_PAGE_SHIFT;
> 
> I couldn't find that the "downstream_ringbuffer_pageoffset" field
> is used anywhere.  Can it just be deleted entirely instead of having
> this really messy calculation?
> 

This field is part of struct vmbus_channel_open_channel, which means
guest-hypervisor communication protocal requires us to set the field,
IIUC. So I don't think we can delete it.

To deal with the messy calculation, I do realize there is a similar
calculation in hv_gpadl_hvpfn() too, so in the next version, I will
add a new helper to do this "send offset in guest virtual address to
send offset in GPADL calculation", and use it here and in
hv_gpadl_hvpfn(). Thoughts?

> >  	open_msg->target_vp = newchannel->target_vp;
> > 
> >  	if (userdatalen)
> > @@ -497,6 +598,7 @@ static int __vmbus_open(struct vmbus_channel *newchannel,
> >  	return err;
> >  }
> > 
> > +
> 
> Spurious add of a blank line?
> 

Yeah, I will fix this, thanks!

Regards,
Boqun

> >  /*
> >   * vmbus_connect_ring - Open the channel but reuse ring buffer
> >   */
> > diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> > index 692c89ccf5df..663f0a016237 100644
> > --- a/include/linux/hyperv.h
> > +++ b/include/linux/hyperv.h
> > @@ -29,6 +29,48 @@
> > 
> >  #pragma pack(push, 1)
> > 
> > +/*
> > + * Types for GPADL, decides is how GPADL header is created.
> > + *
> > + * It doesn't make much difference between BUFFER and RING if PAGE_SIZE is the
> > + * same as HV_HYP_PAGE_SIZE.
> > + *
> > + * If PAGE_SIZE is bigger than HV_HYP_PAGE_SIZE, the headers of ring buffers
> > + * will be of PAGE_SIZE, however, only the first HV_HYP_PAGE will be put
> > + * into gpadl, therefore the number for HV_HYP_PAGE and the indexes of each
> > + * HV_HYP_PAGE will be different between different types of GPADL, for example
> > + * if PAGE_SIZE is 64K:
> > + *
> > + * BUFFER:
> > + *
> > + * gva:    |--       64k      --|--       64k      --| ... |
> > + * gpa:    | 4k | 4k | ... | 4k | 4k | 4k | ... | 4k |
> > + * index:  0    1    2     15   16   17   18 .. 31   32 ...
> > + *         |    |    ...   |    |    |   ...    |   ...
> > + *         v    V          V    V    V          V
> > + * gpadl:  | 4k | 4k | ... | 4k | 4k | 4k | ... | 4k | ... |
> > + * index:  0    1    2 ... 15   16   17   18 .. 31   32 ...
> > + *
> > + * RING:
> > + *
> > + *         | header  |           data           | header  |     data      |
> > + * gva:    |-- 64k --|--       64k      --| ... |-- 64k --|-- 64k --| ... |
> > + * gpa:    | 4k | .. | 4k | 4k | ... | 4k | ... | 4k | .. | 4k | .. | ... |
> > + * index:  0    1    16   17   18    31   ...   n   n+1  n+16 ...         2n
> > + *         |         /    /          /          |         /               /
> > + *         |        /    /          /           |        /               /
> > + *         |       /    /   ...    /    ...     |       /      ...      /
> > + *         |      /    /          /             |      /               /
> > + *         |     /    /          /              |     /               /
> > + *         V    V    V          V               V    V               v
> > + * gpadl:  | 4k | 4k |   ...    |    ...        | 4k | 4k |  ...     |
> > + * index:  0    1    2   ...    16   ...       n-15 n-14 n-13  ...  2n-30
> > + */
> > +enum hv_gpadl_type {
> > +	HV_GPADL_BUFFER,
> > +	HV_GPADL_RING
> > +};
> > +
> >  /* Single-page buffer */
> >  struct hv_page_buffer {
> >  	u32 len;
> > @@ -111,7 +153,7 @@ struct hv_ring_buffer {
> >  	} feature_bits;
> > 
> >  	/* Pad it to PAGE_SIZE so that data starts on page boundary */
> > -	u8	reserved2[4028];
> > +	u8	reserved2[PAGE_SIZE - 68];
> > 
> >  	/*
> >  	 * Ring data starts here + RingDataStartOffset
> > --
> > 2.27.0
> 

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-21  1:41 [RFC 00/11] Hyper-V: Support PAGE_SIZE larger than 4K Boqun Feng
2020-07-21  1:41 ` [RFC 01/11] Drivers: hv: vmbus: Always use HV_HYP_PAGE_SIZE for gpadl Boqun Feng
2020-07-21 15:22   ` Wei Liu
2020-07-22 23:20     ` Boqun Feng
2020-07-21  1:41 ` [RFC 02/11] Drivers: hv: vmbus: Move __vmbus_open() Boqun Feng
2020-07-21 15:23   ` Wei Liu
2020-07-21  1:41 ` [RFC 03/11] Drivers: hv: vmbus: Introduce types of GPADL Boqun Feng
2020-07-22 23:25   ` Michael Kelley
2020-07-22 23:43     ` Boqun Feng [this message]
2020-07-22 23:56       ` Michael Kelley
2020-07-21  1:41 ` [RFC 04/11] Drivers: hv: Use HV_HYP_PAGE in hv_synic_enable_regs() Boqun Feng
2020-07-21  1:41 ` [RFC 05/11] Drivers: hv: vmbus: Move virt_to_hvpfn() to hyperv header Boqun Feng
2020-07-21  1:41 ` [RFC 06/11] hv: hyperv.h: Introduce some hvpfn helper functions Boqun Feng
2020-07-21  1:41 ` [RFC 07/11] hv_netvsc: Use HV_HYP_PAGE_SIZE for Hyper-V communication Boqun Feng
2020-07-21  1:41 ` [RFC 08/11] Input: hyperv-keyboard: Make ringbuffer at least take two pages Boqun Feng
2020-07-21  1:41 ` [RFC 09/11] HID: hyperv: " Boqun Feng
2020-07-22 23:36   ` Michael Kelley
2020-07-23  1:28     ` boqun.feng
2020-07-21  1:41 ` [RFC 10/11] Driver: hv: util: " Boqun Feng
2020-07-21  1:41 ` [RFC 11/11] scsi: storvsc: Support PAGE_SIZE larger than 4K Boqun Feng
2020-07-23  0:13   ` Michael Kelley
2020-07-23  1:51     ` boqun.feng
2020-07-23  2:26       ` Michael Kelley
2020-07-23  3:12         ` Boqun Feng

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