// SPDX-License-Identifier: GPL-2.0-only
/*
*
* Copyright (c) 2009, Microsoft Corporation.
*
* Authors:
* Haiyang Zhang <[email protected]>
* Hank Janssen <[email protected]>
* K. Y. Srinivasan <[email protected]>
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/hyperv.h>
#include <linux/uio.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/prefetch.h>
#include <linux/io.h>
#include <asm/mshyperv.h>
#include "hyperv_vmbus.h"
#define VMBUS_PKT_TRAILER 8
/*
* When we write to the ring buffer, check if the host needs to
* be signaled. Here is the details of this protocol:
*
* 1. The host guarantees that while it is draining the
* ring buffer, it will set the interrupt_mask to
* indicate it does not need to be interrupted when
* new data is placed.
*
* 2. The host guarantees that it will completely drain
* the ring buffer before exiting the read loop. Further,
* once the ring buffer is empty, it will clear the
* interrupt_mask and re-check to see if new data has
* arrived.
*
* KYS: Oct. 30, 2016:
* It looks like Windows hosts have logic to deal with DOS attacks that
* can be triggered if it receives interrupts when it is not expecting
* the interrupt. The host expects interrupts only when the ring
* transitions from empty to non-empty (or full to non full on the guest
* to host ring).
* So, base the signaling decision solely on the ring state until the
* host logic is fixed.
*/
static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
{
struct hv_ring_buffer_info *rbi = &channel->outbound;
virt_mb();
if (READ_ONCE(rbi->ring_buffer->interrupt_mask))
return;
/* check interrupt_mask before read_index */
virt_rmb();
/*
* This is the only case we need to signal when the
* ring transitions from being empty to non-empty.
*/
if (old_write == READ_ONCE(rbi->ring_buffer->read_index)) {
++channel->intr_out_empty;
vmbus_setevent(channel);
}
}
/* Get the next write location for the specified ring buffer. */
static inline u32
hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
{
u32 next = ring_info->ring_buffer->write_index;
return next;
}
/* Set the next write location for the specified ring buffer. */
static inline void
hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
u32 next_write_location)
{
ring_info->ring_buffer->write_index = next_write_location;
}
/* Get the size of the ring buffer. */
static inline u32
hv_get_ring_buffersize(const struct hv_ring_buffer_info *ring_info)
{
return ring_info->ring_datasize;
}
/* Get the read and write indices as u64 of the specified ring buffer. */
static inline u64
hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
{
return (u64)ring_info->ring_buffer->write_index << 32;
}
/*
* Helper routine to copy from source to ring buffer.
* Assume there is enough room. Handles wrap-around in dest case only!!
*/
static u32 hv_copyto_ringbuffer(
struct hv_ring_buffer_info *ring_info,
u32 start_write_offset,
const void *src,
u32 srclen)
{
void *ring_buffer = hv_get_ring_buffer(ring_info);
u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
memcpy(ring_buffer + start_write_offset, src, srclen);
start_write_offset += srclen;
if (start_write_offset >= ring_buffer_size)
start_write_offset -= ring_buffer_size;
return start_write_offset;
}
/*
*
* hv_get_ringbuffer_availbytes()
*
* Get number of bytes available to read and to write to
* for the specified ring buffer
*/
static void
hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
u32 *read, u32 *write)
{
u32 read_loc, write_loc, dsize;
/* Capture the read/write indices before they changed */
read_loc = READ_ONCE(rbi->ring_buffer->read_index);
write_loc = READ_ONCE(rbi->ring_buffer->write_index);
dsize = rbi->ring_datasize;
*write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
read_loc - write_loc;
*read = dsize - *write;
}
/* Get various debug metrics for the specified ring buffer. */
int hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
struct hv_ring_buffer_debug_info *debug_info)
{
u32 bytes_avail_towrite;
u32 bytes_avail_toread;
mutex_lock(&ring_info->ring_buffer_mutex);
if (!ring_info->ring_buffer) {
mutex_unlock(&ring_info->ring_buffer_mutex);
return -EINVAL;
}
hv_get_ringbuffer_availbytes(ring_info,
&bytes_avail_toread,
&bytes_avail_towrite);
debug_info->bytes_avail_toread = bytes_avail_toread;
debug_info->bytes_avail_towrite = bytes_avail_towrite;
debug_info->current_read_index = ring_info->ring_buffer->read_index;
debug_info->current_write_index = ring_info->ring_buffer->write_index;
debug_info->current_interrupt_mask
= ring_info->ring_buffer->interrupt_mask;
mutex_unlock(&ring_info->ring_buffer_mutex);
return 0;
}
EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);
/* Initialize a channel's ring buffer info mutex locks */
void hv_ringbuffer_pre_init(struct vmbus_channel *channel)
{
mutex_init(&channel->inbound.ring_buffer_mutex);
mutex_init(&channel->outbound.ring_buffer_mutex);
}
/* Initialize the ring buffer. */
int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
struct page *pages, u32 page_cnt, u32 max_pkt_size)
{
struct page **pages_wraparound;
int i;
BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
/*
* First page holds struct hv_ring_buffer, do wraparound mapping for
* the rest.
*/
pages_wraparound = kcalloc(page_cnt * 2 - 1,
sizeof(struct page *),
GFP_KERNEL);
if (!pages_wraparound)
return -ENOMEM;
pages_wraparound[0] = pages;
for (i = 0; i < 2 * (page_cnt - 1); i++)
pages_wraparound[i + 1] =
&pages[i % (page_cnt - 1) + 1];
ring_info->ring_buffer = (struct hv_ring_buffer *)
vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP,
pgprot_decrypted(PAGE_KERNEL));
kfree(pages_wraparound);
if (!ring_info->ring_buffer)
return -ENOMEM;
/*
* Ensure the header page is zero'ed since
* encryption status may have changed.
*/
memset(ring_info->ring_buffer, 0, HV_HYP_PAGE_SIZE);
ring_info->ring_buffer->read_index =
ring_info->ring_buffer->write_index = 0;
/* Set the feature bit for enabling flow control. */
ring_info->ring_buffer->feature_bits.value = 1;
ring_info->ring_size = page_cnt << PAGE_SHIFT;
ring_info->ring_size_div10_reciprocal =
reciprocal_value(ring_info->ring_size / 10);
ring_info->ring_datasize = ring_info->ring_size -
sizeof(struct hv_ring_buffer);
ring_info->priv_read_index = 0;
/* Initialize buffer that holds copies of incoming packets */
if (max_pkt_size) {
ring_info->pkt_buffer = kzalloc(max_pkt_size, GFP_KERNEL);
if (!ring_info->pkt_buffer)
return -ENOMEM;
ring_info->pkt_buffer_size = max_pkt_size;
}
spin_lock_init(&ring_info->ring_lock);
return 0;
}
/* Cleanup the ring buffer. */
void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
{
mutex_lock(&ring_info->ring_buffer_mutex);
vunmap(ring_info->ring_buffer);
ring_info->ring_buffer = NULL;
mutex_unlock(&ring_info->ring_buffer_mutex);
kfree(ring_info->pkt_buffer);
ring_info->pkt_buffer = NULL;
ring_info->pkt_buffer_size = 0;
}
/*
* Check if the ring buffer spinlock is available to take or not; used on
* atomic contexts, like panic path (see the Hyper-V framebuffer driver).
*/
bool hv_ringbuffer_spinlock_busy(struct vmbus_channel *channel)
{
struct hv_ring_buffer_info *rinfo = &channel->outbound;
return spin_is_locked(&rinfo->ring_lock);
}
EXPORT_SYMBOL_GPL(hv_ringbuffer_spinlock_busy);
/* Write to the ring buffer. */
int hv_ringbuffer_write(struct vmbus_channel *channel,
const struct kvec *kv_list, u32 kv_count,
u64 requestid, u64 *trans_id)
{
int i;
u32 bytes_avail_towrite;
u32 totalbytes_towrite = sizeof(u64);
u32 next_write_location;
u32 old_write;
u64 prev_indices;
unsigned long flags;
struct hv_ring_buffer_info *outring_info = &channel->outbound;
struct vmpacket_descriptor *desc = kv_list[0].iov_base;
u64 __trans_id, rqst_id = VMBUS_NO_RQSTOR;
if (channel->rescind)
return -ENODEV;
for (i = 0; i < kv_count; i++)
totalbytes_towrite += kv_list[i].iov_len;
spin_lock_irqsave(&outring_info->ring_lock, flags);
bytes_avail_towrite = hv_get_bytes_to_write(outring_info);
/*
* If there is only room for the packet, assume it is full.
* Otherwise, the next time around, we think the ring buffer
* is empty since the read index == write index.
*/
if (bytes_avail_towrite <= totalbytes_towrite) {
++channel->out_full_total;
if (!channel->out_full_flag) {
++channel->out_full_first;
channel->out_full_flag = true;
}
spin_unlock_irqrestore(&outring_info->ring_lock, flags);
return -EAGAIN;
}
channel->out_full_flag = false;
/* Write to the ring buffer */
next_write_location = hv_get_next_write_location(outring_info);
old_write = next_write_location;
for (i = 0; i < kv_count; i++) {
next_write_location = hv_copyto_ringbuffer(outring_info,
next_write_location,
kv_list[i].iov_base,
kv_list[i].iov_len);
}
/*
* Allocate the request ID after the data has been copied into the
* ring buffer. Once this request ID is allocated, the completion
* path could find the data and free it.
*/
if (desc->flags == VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED) {
if (channel->next_request_id_callback != NULL) {
rqst_id = channel->next_request_id_callback(channel, requestid);
if (rqst_id == VMBUS_RQST_ERROR) {
spin_unlock_irqrestore(&outring_info->ring_lock, flags);
return -EAGAIN;
}
}
}
desc = hv_get_ring_buffer(outring_info) + old_write;
__trans_id = (rqst_id == VMBUS_NO_RQSTOR) ? requestid : rqst_id;
/*
* Ensure the compiler doesn't generate code that reads the value of
* the transaction ID from the ring buffer, which is shared with the
* Hyper-V host and subject to being changed at any time.
*/
WRITE_ONCE(desc->trans_id, __trans_id);
if (trans_id)
*trans_id = __trans_id;
/* Set previous packet start */
prev_indices = hv_get_ring_bufferindices(outring_info);
next_write_location = hv_copyto_ringbuffer(outring_info,
next_write_location,
&prev_indices,
sizeof(u64));
/* Issue a full memory barrier before updating the write index */
virt_mb();
/* Now, update the write location */
hv_set_next_write_location(outring_info, next_write_location);
spin_unlock_irqrestore(&outring_info->ring_lock, flags);
hv_signal_on_write(old_write, channel);
if (channel->rescind) {
if (rqst_id != VMBUS_NO_RQSTOR) {
/* Reclaim request ID to avoid leak of IDs */
if (channel->request_addr_callback != NULL)
channel->request_addr_callback(channel, rqst_id);
}
return -ENODEV;
}
return 0;
}
int hv_ringbuffer_read(struct vmbus_channel *channel,
void *buffer, u32 buflen, u32 *buffer_actual_len,
u64 *requestid, bool raw)
{
struct vmpacket_descriptor *desc;
u32 packetlen, offset;
if (unlikely(buflen == 0))
return -EINVAL;
*buffer_actual_len = 0;
*requestid = 0;
/* Make sure there is something to read */
desc = hv_pkt_iter_first(channel);
if (desc == NULL) {
/*
* No error is set when there is even no header, drivers are
* supposed to analyze buffer_actual_len.
*/
return 0;
}
offset = raw ? 0 : (desc->offset8 << 3);
packetlen = (desc->len8 << 3) - offset;
*buffer_actual_len = packetlen;
*requestid = desc->trans_id;
if (unlikely(packetlen > buflen))
return -ENOBUFS;
/* since ring is double mapped, only one copy is necessary */
memcpy(buffer, (const char *)desc + offset, packetlen);
/* Advance ring index to next packet descriptor */
__hv_pkt_iter_next(channel, desc);
/* Notify host of update */
hv_pkt_iter_close(channel);
return 0;
}
/*
* Determine number of bytes available in ring buffer after
* the current iterator (priv_read_index) location.
*
* This is similar to hv_get_bytes_to_read but with private
* read index instead.
*/
static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi)
{
u32 priv_read_loc = rbi->priv_read_index;
u32 write_loc;
/*
* The Hyper-V host writes the packet data, then uses
* store_release() to update the write_index. Use load_acquire()
* here to prevent loads of the packet data from being re-ordered
* before the read of the write_index and potentially getting
* stale data.
*/
write_loc = virt_load_acquire(&rbi->ring_buffer->write_index);
if (write_loc >= priv_read_loc)
return write_loc - priv_read_loc;
else
return (rbi->ring_datasize - priv_read_loc) + write_loc;
}
/*
* Get first vmbus packet from ring buffer after read_index
*
* If ring buffer is empty, returns NULL and no other action needed.
*/
struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
{
struct hv_ring_buffer_info *rbi = &channel->inbound;
struct vmpacket_descriptor *desc, *desc_copy;
u32 bytes_avail, pkt_len, pkt_offset;
hv_debug_delay_test(channel, MESSAGE_DELAY);
bytes_avail = hv_pkt_iter_avail(rbi);
if (bytes_avail < sizeof(struct vmpacket_descriptor))
return NULL;
bytes_avail = min(rbi->pkt_buffer_size, bytes_avail);
desc = (struct vmpacket_descriptor *)(hv_get_ring_buffer(rbi) + rbi->priv_read_index);
/*
* Ensure the compiler does not use references to incoming Hyper-V values (which
* could change at any moment) when reading local variables later in the code
*/
pkt_len = READ_ONCE(desc->len8) << 3;
pkt_offset = READ_ONCE(desc->offset8) << 3;
/*
* If pkt_len is invalid, set it to the smaller of hv_pkt_iter_avail() and
* rbi->pkt_buffer_size
*/
if (pkt_len < sizeof(struct vmpacket_descriptor) || pkt_len > bytes_avail)
pkt_len = bytes_avail;
/*
* If pkt_offset is invalid, arbitrarily set it to
* the size of vmpacket_descriptor
*/
if (pkt_offset < sizeof(struct vmpacket_descriptor) || pkt_offset > pkt_len)
pkt_offset = sizeof(struct vmpacket_descriptor);
/* Copy the Hyper-V packet out of the ring buffer */
desc_copy = (struct vmpacket_descriptor *)rbi->pkt_buffer;
memcpy(desc_copy, desc, pkt_len);
/*
* Hyper-V could still change len8 and offset8 after the earlier read.
* Ensure that desc_copy has legal values for len8 and offset8 that
* are consistent with the copy we just made
*/
desc_copy->len8 = pkt_len >> 3;
desc_copy->offset8 = pkt_offset >> 3;
return desc_copy;
}
EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
/*
* Get next vmbus packet from ring buffer.
*
* Advances the current location (priv_read_index) and checks for more
* data. If the end of the ring buffer is reached, then return NULL.
*/
struct vmpacket_descriptor *
__hv_pkt_iter_next(struct vmbus_channel *channel,
const struct vmpacket_descriptor *desc)
{
struct hv_ring_buffer_info *rbi = &channel->inbound;
u32 packetlen = desc->len8 << 3;
u32 dsize = rbi->ring_datasize;
hv_debug_delay_test(channel, MESSAGE_DELAY);
/* bump offset to next potential packet */
rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
if (rbi->priv_read_index >= dsize)
rbi->priv_read_index -= dsize;
/* more data? */
return hv_pkt_iter_first(channel);
}
EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
/* How many bytes were read in this iterator cycle */
static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
u32 start_read_index)
{
if (rbi->priv_read_index >= start_read_index)
return rbi->priv_read_index - start_read_index;
else
return rbi->ring_datasize - start_read_index +
rbi->priv_read_index;
}
/*
* Update host ring buffer after iterating over packets. If the host has
* stopped queuing new entries because it found the ring buffer full, and
* sufficient space is being freed up, signal the host. But be careful to
* only signal the host when necessary, both for performance reasons and
* because Hyper-V protects itself by throttling guests that signal
* inappropriately.
*
* Determining when to signal is tricky. There are three key data inputs
* that must be handled in this order to avoid race conditions:
*
* 1. Update the read_index
* 2. Read the pending_send_sz
* 3. Read the current write_index
*
* The interrupt_mask is not used to determine when to signal. The
* interrupt_mask is used only on the guest->host ring buffer when
* sending requests to the host. The host does not use it on the host->
* guest ring buffer to indicate whether it should be signaled.
*/
void hv_pkt_iter_close(struct vmbus_channel *channel)
{
struct hv_ring_buffer_info *rbi = &channel->inbound;
u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
/*
* Make sure all reads are done before we update the read index since
* the writer may start writing to the read area once the read index
* is updated.
*/
virt_rmb();
start_read_index = rbi->ring_buffer->read_index;
rbi->ring_buffer->read_index = rbi->priv_read_index;
/*
* Older versions of Hyper-V (before WS2102 and Win8) do not
* implement pending_send_sz and simply poll if the host->guest
* ring buffer is full. No signaling is needed or expected.
*/
if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
return;
/*
* Issue a full memory barrier before making the signaling decision.
* If reading pending_send_sz were to be reordered and happen
* before we commit the new read_index, a race could occur. If the
* host were to set the pending_send_sz after we have sampled
* pending_send_sz, and the ring buffer blocks before we commit the
* read index, we could miss sending the interrupt. Issue a full
* memory barrier to address this.
*/
virt_mb();
/*
* If the pending_send_sz is zero, then the ring buffer is not
* blocked and there is no need to signal. This is far by the
* most common case, so exit quickly for best performance.
*/
pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
if (!pending_sz)
return;
/*
* Ensure the read of write_index in hv_get_bytes_to_write()
* happens after the read of pending_send_sz.
*/
virt_rmb();
curr_write_sz = hv_get_bytes_to_write(rbi);
bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
/*
* We want to signal the host only if we're transitioning
* from a "not enough free space" state to a "enough free
* space" state. For example, it's possible that this function
* could run and free up enough space to signal the host, and then
* run again and free up additional space before the host has a
* chance to clear the pending_send_sz. The 2nd invocation would
* be a null transition from "enough free space" to "enough free
* space", which doesn't warrant a signal.
*
* Exactly filling the ring buffer is treated as "not enough
* space". The ring buffer always must have at least one byte
* empty so the empty and full conditions are distinguishable.
* hv_get_bytes_to_write() doesn't fully tell the truth in
* this regard.
*
* So first check if we were in the "enough free space" state
* before we began the iteration. If so, the host was not
* blocked, and there's no need to signal.
*/
if (curr_write_sz - bytes_read > pending_sz)
return;
/*
* Similarly, if the new state is "not enough space", then
* there's no need to signal.
*/
if (curr_write_sz <= pending_sz)
return;
++channel->intr_in_full;
vmbus_setevent(channel);
}
EXPORT_SYMBOL_GPL(hv_pkt_iter_close);
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