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Message-ID: <MW2PR2101MB10525571DACE6447A8C269B8D7790@MW2PR2101MB1052.namprd21.prod.outlook.com>
Date: Wed, 22 Jul 2020 23:56:41 +0000
From: Michael Kelley <mikelley@...rosoft.com>
To: Boqun Feng <boqun.feng@...il.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
From: Boqun Feng <boqun.feng@...il.com> Sent: Wednesday, July 22, 2020 4:43 PM
>
> 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.
Indeed, you are right. I mis-read it as a field in struct vmbus_channel,
but that's not the case. Thanks.
>
> 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?
Yes, that helps.
>
> > > 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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