diff options
Diffstat (limited to 'drivers/hv/ring_buffer.c')
| -rw-r--r-- | drivers/hv/ring_buffer.c | 572 |
1 files changed, 572 insertions, 0 deletions
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c new file mode 100644 index 000000000..7ed6fad3f --- /dev/null +++ b/drivers/hv/ring_buffer.c @@ -0,0 +1,572 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * + * Copyright (c) 2009, Microsoft Corporation. + * + * Authors: + * Haiyang Zhang <haiyangz@microsoft.com> + * Hank Janssen <hjanssen@microsoft.com> + * K. Y. Srinivasan <kys@microsoft.com> + */ +#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 "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; +} + +/* Set the next read location for the specified ring buffer. */ +static inline void +hv_set_next_read_location(struct hv_ring_buffer_info *ring_info, + u32 next_read_location) +{ + ring_info->ring_buffer->read_index = next_read_location; + ring_info->priv_read_index = next_read_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) +{ + int i; + struct page **pages_wraparound; + + 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, PAGE_KERNEL); + + kfree(pages_wraparound); + + + if (!ring_info->ring_buffer) + return -ENOMEM; + + 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; + + 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); +} + +/* + * 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) +{ + 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; + + 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); + } + + /* 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) + 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; + + hv_debug_delay_test(channel, MESSAGE_DELAY); + if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor)) + return NULL; + + desc = hv_get_ring_buffer(rbi) + rbi->priv_read_index; + if (desc) + prefetch((char *)desc + (desc->len8 << 3)); + + return desc; +} +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); |