Date:   Wed, 2 Aug 2023 21:43:54 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Saurabh Sengar <ssengar@...ux.microsoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "corbet@....net" <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: RE: [PATCH v3 2/3] tools: hv: Add vmbus_bufring

From: Saurabh Sengar <ssengar@...ux.microsoft.com> Sent: Friday, July 14, 2023 3:26 AM
> 
> Provide a userspace interface for userspace drivers or applications to
> read/write a VMBus ringbuffer. A significant part of this code is
> borrowed from DPDK[1]. Current library is supported exclusively for
> the x86 architecture.
> 
> To build this library:
> make -C tools/hv libvmbus_bufring.a
> 
> Applications using this library can include the vmbus_bufring.h header
> file and libvmbus_bufring.a statically.
> 
> [1] https://github.com/DPDK/dpdk/
> 
> Signed-off-by: Mary Hardy <maryhardy@...rosoft.com>
> Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> ---
> [V3]
> - Made ring buffer data offset depend on page size
> - remove rte_smp_rwmb macro and reused rte_compiler_barrier instead
> - Added legal counsel sign-off
> - Removed "Link:" tag
> - Improve commit messages
> - new library compilation dependent on x86
> - simplify mmap
> 
> [V2]
> - simpler sysfs path, less parsing
> 
>  tools/hv/Build           |   1 +
>  tools/hv/Makefile        |  13 +-
>  tools/hv/vmbus_bufring.c | 297 +++++++++++++++++++++++++++++++++++++++
>  tools/hv/vmbus_bufring.h | 154 ++++++++++++++++++++
>  4 files changed, 464 insertions(+), 1 deletion(-)
>  create mode 100644 tools/hv/vmbus_bufring.c
>  create mode 100644 tools/hv/vmbus_bufring.h
> 
> diff --git a/tools/hv/Build b/tools/hv/Build
> index 6cf51fa4b306..2a667d3d94cb 100644
> --- a/tools/hv/Build
> +++ b/tools/hv/Build
> @@ -1,3 +1,4 @@
>  hv_kvp_daemon-y += hv_kvp_daemon.o
>  hv_vss_daemon-y += hv_vss_daemon.o
>  hv_fcopy_daemon-y += hv_fcopy_daemon.o
> +vmbus_bufring-y += vmbus_bufring.o
> diff --git a/tools/hv/Makefile b/tools/hv/Makefile
> index fe770e679ae8..33cf488fd20f 100644
> --- a/tools/hv/Makefile
> +++ b/tools/hv/Makefile
> @@ -11,14 +11,19 @@ srctree := $(patsubst %/,%,$(dir $(CURDIR)))
>  srctree := $(patsubst %/,%,$(dir $(srctree)))
>  endif
> 
> +include $(srctree)/tools/scripts/Makefile.arch
> +
>  # Do not use make's built-in rules
>  # (this improves performance and avoids hard-to-debug behaviour);
>  MAKEFLAGS += -r
> 
>  override CFLAGS += -O2 -Wall -g -D_GNU_SOURCE -I$(OUTPUT)include
> 
> +ifeq ($(SRCARCH),x86)
> +ALL_LIBS := libvmbus_bufring.a
> +endif
>  ALL_TARGETS := hv_kvp_daemon hv_vss_daemon hv_fcopy_daemon
> -ALL_PROGRAMS := $(patsubst %,$(OUTPUT)%,$(ALL_TARGETS))
> +ALL_PROGRAMS := $(patsubst %,$(OUTPUT)%,$(ALL_TARGETS)) $(patsubst
> %,$(OUTPUT)%,$(ALL_LIBS))
> 
>  ALL_SCRIPTS := hv_get_dhcp_info.sh hv_get_dns_info.sh hv_set_ifconfig.sh
> 
> @@ -27,6 +32,12 @@ all: $(ALL_PROGRAMS)
>  export srctree OUTPUT CC LD CFLAGS
>  include $(srctree)/tools/build/Makefile.include
> 
> +HV_VMBUS_BUFRING_IN := $(OUTPUT)vmbus_bufring.o
> +$(HV_VMBUS_BUFRING_IN): FORCE
> +	$(Q)$(MAKE) $(build)=vmbus_bufring
> +$(OUTPUT)libvmbus_bufring.a : vmbus_bufring.o
> +	$(AR) rcs $@ $^
> +
>  HV_KVP_DAEMON_IN := $(OUTPUT)hv_kvp_daemon-in.o
>  $(HV_KVP_DAEMON_IN): FORCE
>  	$(Q)$(MAKE) $(build)=hv_kvp_daemon
> diff --git a/tools/hv/vmbus_bufring.c b/tools/hv/vmbus_bufring.c
> new file mode 100644
> index 000000000000..fb1f0489c625
> --- /dev/null
> +++ b/tools/hv/vmbus_bufring.c
> @@ -0,0 +1,297 @@
> +// SPDX-License-Identifier: BSD-3-Clause
> +/*
> + * Copyright (c) 2009-2012,2016,2023 Microsoft Corp.
> + * Copyright (c) 2012 NetApp Inc.
> + * Copyright (c) 2012 Citrix Inc.
> + * All rights reserved.
> + */
> +
> +#include <errno.h>
> +#include <emmintrin.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/uio.h>
> +#include "vmbus_bufring.h"
> +
> +#define	rte_compiler_barrier()	({ asm volatile ("" : : : "memory"); })
> +#define RINGDATA_START_OFFSET	(getpagesize())
> +#define VMBUS_RQST_ERROR	0xFFFFFFFFFFFFFFFF
> +#define ALIGN(val, align)	((typeof(val))((val) & (~((typeof(val))((align) - 1)))))
> +
> +/* Increase bufring index by inc with wraparound */
> +static inline uint32_t vmbus_br_idxinc(uint32_t idx, uint32_t inc, uint32_t sz)
> +{
> +	idx += inc;
> +	if (idx >= sz)
> +		idx -= sz;
> +
> +	return idx;
> +}
> +
> +void vmbus_br_setup(struct vmbus_br *br, void *buf, unsigned int blen)
> +{
> +	br->vbr = buf;
> +	br->windex = br->vbr->windex;
> +	br->dsize = blen - RINGDATA_START_OFFSET;
> +}
> +
> +static inline __always_inline void
> +rte_smp_mb(void)
> +{
> +	asm volatile("lock addl $0, -128(%%rsp); " ::: "memory");
> +}
> +
> +static inline int
> +rte_atomic32_cmpset(volatile uint32_t *dst, uint32_t exp, uint32_t src)
> +{
> +	uint8_t res;
> +
> +	asm volatile("lock ; "
> +		     "cmpxchgl %[src], %[dst];"
> +		     "sete %[res];"
> +		     : [res] "=a" (res),     /* output */
> +		     [dst] "=m" (*dst)
> +		     : [src] "r" (src),      /* input */
> +		     "a" (exp),
> +		     "m" (*dst)
> +		     : "memory");            /* no-clobber list */
> +	return res;
> +}
> +
> +static inline uint32_t
> +vmbus_txbr_copyto(const struct vmbus_br *tbr, uint32_t windex,
> +		  const void *src0, uint32_t cplen)
> +{
> +	uint8_t *br_data = (uint8_t *)tbr->vbr + RINGDATA_START_OFFSET;
> +	uint32_t br_dsize = tbr->dsize;
> +	const uint8_t *src = src0;
> +
> +	if (cplen > br_dsize - windex) {
> +		uint32_t fraglen = br_dsize - windex;
> +
> +		/* Wrap-around detected */
> +		memcpy(br_data + windex, src, fraglen);
> +		memcpy(br_data, src + fraglen, cplen - fraglen);
> +	} else {
> +		memcpy(br_data + windex, src, cplen);
> +	}
> +
> +	return vmbus_br_idxinc(windex, cplen, br_dsize);
> +}
> +
> +/*
> + * Write scattered channel packet to TX bufring.
> + *
> + * The offset of this channel packet is written as a 64bits value
> + * immediately after this channel packet.
> + *
> + * The write goes through three stages:
> + *  1. Reserve space in ring buffer for the new data.
> + *     Writer atomically moves priv_write_index.
> + *  2. Copy the new data into the ring.
> + *  3. Update the tail of the ring (visible to host) that indicates
> + *     next read location. Writer updates write_index
> + */
> +static int
> +vmbus_txbr_write(struct vmbus_br *tbr, const struct iovec iov[], int iovlen,
> +		 bool *need_sig)
> +{
> +	struct vmbus_bufring *vbr = tbr->vbr;
> +	uint32_t ring_size = tbr->dsize;
> +	uint32_t old_windex, next_windex, windex, total;
> +	uint64_t save_windex;
> +	int i;
> +
> +	total = 0;
> +	for (i = 0; i < iovlen; i++)
> +		total += iov[i].iov_len;
> +	total += sizeof(save_windex);
> +
> +	/* Reserve space in ring */
> +	do {
> +		uint32_t avail;
> +
> +		/* Get current free location */
> +		old_windex = tbr->windex;
> +
> +		/* Prevent compiler reordering this with calculation */
> +		rte_compiler_barrier();
> +
> +		avail = vmbus_br_availwrite(tbr, old_windex);
> +
> +		/* If not enough space in ring, then tell caller. */
> +		if (avail <= total)
> +			return -EAGAIN;
> +
> +		next_windex = vmbus_br_idxinc(old_windex, total, ring_size);
> +
> +		/* Atomic update of next write_index for other threads */
> +	} while (!rte_atomic32_cmpset(&tbr->windex, old_windex, next_windex));
> +
> +	/* Space from old..new is now reserved */
> +	windex = old_windex;
> +	for (i = 0; i < iovlen; i++)
> +		windex = vmbus_txbr_copyto(tbr, windex, iov[i].iov_base, iov[i].iov_len);
> +
> +	/* Set the offset of the current channel packet. */
> +	save_windex = ((uint64_t)old_windex) << 32;
> +	windex = vmbus_txbr_copyto(tbr, windex, &save_windex,
> +				   sizeof(save_windex));
> +
> +	/* The region reserved should match region used */
> +	if (windex != next_windex)
> +		return -EINVAL;
> +
> +	/* Ensure that data is available before updating host index */
> +	rte_compiler_barrier();
> +
> +	/* Checkin for our reservation. wait for our turn to update host */
> +	while (!rte_atomic32_cmpset(&vbr->windex, old_windex, next_windex))
> +		_mm_pause();
> +
> +	return 0;
> +}
> +
> +int rte_vmbus_chan_send(struct vmbus_br *txbr, uint16_t type, void *data,
> +			uint32_t dlen, uint32_t flags)
> +{
> +	struct vmbus_chanpkt pkt;
> +	unsigned int pktlen, pad_pktlen;
> +	const uint32_t hlen = sizeof(pkt);
> +	bool send_evt = false;
> +	uint64_t pad = 0;
> +	struct iovec iov[3];
> +	int error;
> +
> +	pktlen = hlen + dlen;
> +	pad_pktlen = ALIGN(pktlen, sizeof(uint64_t));

This ALIGN function rounds down.  So pad_pktlen could be
less than pktlen.

> +
> +	pkt.hdr.type = type;
> +	pkt.hdr.flags = flags;
> +	pkt.hdr.hlen = hlen >> VMBUS_CHANPKT_SIZE_SHIFT;
> +	pkt.hdr.tlen = pad_pktlen >> VMBUS_CHANPKT_SIZE_SHIFT;
> +	pkt.hdr.xactid = VMBUS_RQST_ERROR; /* doesn't support multiple requests at same time */
> +
> +	iov[0].iov_base = &pkt;
> +	iov[0].iov_len = hlen;
> +	iov[1].iov_base = data;
> +	iov[1].iov_len = dlen;
> +	iov[2].iov_base = &pad;
> +	iov[2].iov_len = pad_pktlen - pktlen;

Given the way your ALIGN function works, the above could
produce a negative value for iov[2].iov_len.  Then bad things
will happen. :-(

> +
> +	error = vmbus_txbr_write(txbr, iov, 3, &send_evt);
> +
> +	return error;
> +}
> +
> +static inline uint32_t
> +vmbus_rxbr_copyfrom(const struct vmbus_br *rbr, uint32_t rindex,
> +		    void *dst0, size_t cplen)
> +{
> +	const uint8_t *br_data = (uint8_t *)rbr->vbr + RINGDATA_START_OFFSET;
> +	uint32_t br_dsize = rbr->dsize;
> +	uint8_t *dst = dst0;
> +
> +	if (cplen > br_dsize - rindex) {
> +		uint32_t fraglen = br_dsize - rindex;
> +
> +		/* Wrap-around detected. */
> +		memcpy(dst, br_data + rindex, fraglen);
> +		memcpy(dst + fraglen, br_data, cplen - fraglen);
> +	} else {
> +		memcpy(dst, br_data + rindex, cplen);
> +	}
> +
> +	return vmbus_br_idxinc(rindex, cplen, br_dsize);
> +}
> +
> +/* Copy data from receive ring but don't change index */
> +static int
> +vmbus_rxbr_peek(const struct vmbus_br *rbr, void *data, size_t dlen)
> +{
> +	uint32_t avail;
> +
> +	/*
> +	 * The requested data and the 64bits channel packet
> +	 * offset should be there at least.
> +	 */
> +	avail = vmbus_br_availread(rbr);
> +	if (avail < dlen + sizeof(uint64_t))
> +		return -EAGAIN;
> +
> +	vmbus_rxbr_copyfrom(rbr, rbr->vbr->rindex, data, dlen);
> +	return 0;
> +}
> +
> +/*
> + * Copy data from receive ring and change index
> + * NOTE:
> + * We assume (dlen + skip) == sizeof(channel packet).
> + */
> +static int
> +vmbus_rxbr_read(struct vmbus_br *rbr, void *data, size_t dlen, size_t skip)
> +{
> +	struct vmbus_bufring *vbr = rbr->vbr;
> +	uint32_t br_dsize = rbr->dsize;
> +	uint32_t rindex;
> +
> +	if (vmbus_br_availread(rbr) < dlen + skip + sizeof(uint64_t))
> +		return -EAGAIN;
> +
> +	/* Record where host was when we started read (for debug) */
> +	rbr->windex = rbr->vbr->windex;
> +
> +	/*
> +	 * Copy channel packet from RX bufring.
> +	 */
> +	rindex = vmbus_br_idxinc(rbr->vbr->rindex, skip, br_dsize);
> +	rindex = vmbus_rxbr_copyfrom(rbr, rindex, data, dlen);
> +
> +	/*
> +	 * Discard this channel packet's 64bits offset, which is useless to us.
> +	 */
> +	rindex = vmbus_br_idxinc(rindex, sizeof(uint64_t), br_dsize);
> +
> +	/* Update the read index _after_ the channel packet is fetched.	 */
> +	rte_compiler_barrier();
> +
> +	vbr->rindex = rindex;
> +
> +	return 0;
> +}
> +
> +int rte_vmbus_chan_recv_raw(struct vmbus_br *rxbr,
> +			    void *data, uint32_t *len)
> +{
> +	struct vmbus_chanpkt_hdr pkt;
> +	uint32_t dlen, bufferlen = *len;
> +	int error;
> +
> +	error = vmbus_rxbr_peek(rxbr, &pkt, sizeof(pkt));
> +	if (error)
> +		return error;
> +
> +	if (unlikely(pkt.hlen < VMBUS_CHANPKT_HLEN_MIN))
> +		/* XXX this channel is dead actually. */
> +		return -EIO;
> +
> +	if (unlikely(pkt.hlen > pkt.tlen))
> +		return -EIO;
> +
> +	/* Length are in quad words */
> +	dlen = pkt.tlen << VMBUS_CHANPKT_SIZE_SHIFT;
> +	*len = dlen;
> +
> +	/* If caller buffer is not large enough */
> +	if (unlikely(dlen > bufferlen))
> +		return -ENOBUFS;
> +
> +	/* Read data and skip packet header */
> +	error = vmbus_rxbr_read(rxbr, data, dlen, 0);
> +	if (error)
> +		return error;
> +
> +	/* Return the number of bytes read */
> +	return dlen + sizeof(uint64_t);
> +}
> diff --git a/tools/hv/vmbus_bufring.h b/tools/hv/vmbus_bufring.h
> new file mode 100644
> index 000000000000..45ecc48e517f
> --- /dev/null
> +++ b/tools/hv/vmbus_bufring.h
> @@ -0,0 +1,154 @@
> +/* SPDX-License-Identifier: BSD-3-Clause */
> +
> +#ifndef _VMBUS_BUF_H_
> +#define _VMBUS_BUF_H_
> +
> +#include <stdbool.h>
> +#include <stdint.h>
> +
> +#define __packed   __attribute__((__packed__))
> +#define unlikely(x)	__builtin_expect(!!(x), 0)
> +
> +#define ICMSGHDRFLAG_TRANSACTION	1
> +#define ICMSGHDRFLAG_REQUEST		2
> +#define ICMSGHDRFLAG_RESPONSE		4
> +
> +#define IC_VERSION_NEGOTIATION_MAX_VER_COUNT 100
> +#define ICMSG_HDR (sizeof(struct vmbuspipe_hdr) + sizeof(struct icmsg_hdr))
> +#define ICMSG_NEGOTIATE_PKT_SIZE(icframe_vercnt, icmsg_vercnt) \
> +	(ICMSG_HDR + sizeof(struct icmsg_negotiate) + \
> +	 (((icframe_vercnt) + (icmsg_vercnt)) * sizeof(struct ic_version)))
> +
> +/*
> + * Channel packets
> + */
> +
> +/* Channel packet flags */
> +#define VMBUS_CHANPKT_TYPE_INBAND	0x0006
> +#define VMBUS_CHANPKT_TYPE_RXBUF	0x0007
> +#define VMBUS_CHANPKT_TYPE_GPA		0x0009
> +#define VMBUS_CHANPKT_TYPE_COMP		0x000b
> +
> +#define VMBUS_CHANPKT_FLAG_NONE		0
> +#define VMBUS_CHANPKT_FLAG_RC		0x0001  /* report completion */
> +
> +#define VMBUS_CHANPKT_SIZE_SHIFT	3
> +#define VMBUS_CHANPKT_SIZE_ALIGN	BIT(VMBUS_CHANPKT_SIZE_SHIFT)
> +#define VMBUS_CHANPKT_HLEN_MIN		\
> +	(sizeof(struct vmbus_chanpkt_hdr) >> VMBUS_CHANPKT_SIZE_SHIFT)
> +
> +/*
> + * Buffer ring
> + */
> +struct vmbus_bufring {
> +	volatile uint32_t windex;
> +	volatile uint32_t rindex;
> +
> +	/*
> +	 * Interrupt mask {0,1}
> +	 *
> +	 * For TX bufring, host set this to 1, when it is processing
> +	 * the TX bufring, so that we can safely skip the TX event
> +	 * notification to host.
> +	 *
> +	 * For RX bufring, once this is set to 1 by us, host will not
> +	 * further dispatch interrupts to us, even if there are data
> +	 * pending on the RX bufring.  This effectively disables the
> +	 * interrupt of the channel to which this RX bufring is attached.
> +	 */
> +	volatile uint32_t imask;
> +
> +	/*
> +	 * Win8 uses some of the reserved bits to implement
> +	 * interrupt driven flow management. On the send side
> +	 * we can request that the receiver interrupt the sender
> +	 * when the ring transitions from being full to being able
> +	 * to handle a message of size "pending_send_sz".
> +	 *
> +	 * Add necessary state for this enhancement.
> +	 */
> +	volatile uint32_t pending_send;
> +	uint32_t reserved1[12];
> +
> +	union {
> +		struct {
> +			uint32_t feat_pending_send_sz:1;
> +		};
> +		uint32_t value;
> +	} feature_bits;
> +
> +	/*
> +	 * Ring data starts here + RingDataStartOffset

This mention of RingDataStartOffset looks stale.  I could
not find it defined anywhere.

> +	 * !!! DO NOT place any fields below this !!!
> +	 */
> +	uint8_t data[];
> +} __packed;
> +
> +struct vmbus_br {
> +	struct vmbus_bufring *vbr;
> +	uint32_t	dsize;
> +	uint32_t	windex; /* next available location */
> +};
> +
> +struct vmbus_chanpkt_hdr {
> +	uint16_t	type;	/* VMBUS_CHANPKT_TYPE_ */
> +	uint16_t	hlen;	/* header len, in 8 bytes */
> +	uint16_t	tlen;	/* total len, in 8 bytes */
> +	uint16_t	flags;	/* VMBUS_CHANPKT_FLAG_ */
> +	uint64_t	xactid;
> +} __packed;
> +
> +struct vmbus_chanpkt {
> +	struct vmbus_chanpkt_hdr hdr;
> +} __packed;
> +
> +struct vmbuspipe_hdr {
> +	unsigned int flags;
> +	unsigned int msgsize;
> +} __packed;
> +
> +struct ic_version {
> +	unsigned short major;
> +	unsigned short minor;
> +} __packed;
> +
> +struct icmsg_negotiate {
> +	unsigned short icframe_vercnt;
> +	unsigned short icmsg_vercnt;
> +	unsigned int reserved;
> +	struct ic_version icversion_data[]; /* any size array */
> +} __packed;
> +
> +struct icmsg_hdr {
> +	struct ic_version icverframe;
> +	unsigned short icmsgtype;
> +	struct ic_version icvermsg;
> +	unsigned short icmsgsize;
> +	unsigned int status;
> +	unsigned char ictransaction_id;
> +	unsigned char icflags;
> +	unsigned char reserved[2];
> +} __packed;
> +
> +int rte_vmbus_chan_recv_raw(struct vmbus_br *rxbr, void *data, uint32_t *len);
> +int rte_vmbus_chan_send(struct vmbus_br *txbr, uint16_t type, void *data,
> +			uint32_t dlen, uint32_t flags);
> +void vmbus_br_setup(struct vmbus_br *br, void *buf, unsigned int blen);
> +
> +/* Amount of space available for write */
> +static inline uint32_t vmbus_br_availwrite(const struct vmbus_br *br, uint32_t
> windex)
> +{
> +	uint32_t rindex = br->vbr->rindex;
> +
> +	if (windex >= rindex)
> +		return br->dsize - (windex - rindex);
> +	else
> +		return rindex - windex;
> +}
> +
> +static inline uint32_t vmbus_br_availread(const struct vmbus_br *br)
> +{
> +	return br->dsize - vmbus_br_availwrite(br, br->vbr->windex);
> +}
> +
> +#endif	/* !_VMBUS_BUF_H_ */
> --
> 2.34.1

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