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Date: Thu, 23 Jul 2020 07:43:21 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: Michael Kelley <mikelley@...rosoft.com>
Cc: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
KY 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>
Subject: Re: [RFC 03/11] Drivers: hv: vmbus: Introduce types of GPADL
On Wed, Jul 22, 2020 at 11:25:18PM +0000, Michael Kelley wrote:
> From: Boqun Feng <boqun.feng@...il.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@...il.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
>
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