gve: Add header split data path

Add header buffers and ethtool support to enable header split via the
tcp-data-split flag in ethtool's ringparam config. A coherent dma memory
is allocated for the header buffers. There is one header buffer per ring
entry by calculating the offset to the header-buffers starting address.
The header buffer is always copied directly into the skb and payload is
always added as frags. When there is a header buffer overflow or the
header length is 0, the driver places the whole unsplit packet in frags.

When toggling header split, the driver will call gve_adjust_config to
set its queues appropriately. If header split is enabled by the user and
the max packet buffer size is no less than 4KB, driver will set the
packet buffer size as 4KB to support TCP_ZEROCOPY_RECEIVE. Otherwise the
driver will use the default 2KB as the packet buffer size.

`ethtool -G <dev> tcp-data-split on/off` is the command to toggle header
split.
`ethtool -g <dev>` will show the status of header split with the field
of `tcp-data-split`.

Co-developed-by: Ziwei Xiao <ziweixiao@google.com>
Signed-off-by: Ziwei Xiao <ziweixiao@google.com>
Signed-off-by: Jeroen de Borst <jeroendb@google.com>
Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gve: Switch to config-aware queue allocation

The new config-aware functions will help achieve the goal of being able
to allocate resources for new queues while there already are active
queues serving traffic.

These new functions work off of arbitrary queue allocation configs
rather than just the currently active config in priv, and they return
the newly allocated resources instead of writing them into priv.

Signed-off-by: Shailend Chand <shailend@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Jeroen de Borst <jeroendb@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240122182632.1102721-4-shailend@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

gve: Refactor napi add and remove functions

This change makes the napi poll functions non-static and moves the
gve_(add|remove)_napi functions to gve_utils.c, to make possible future
"start queue" hooks in the datapath files.

Signed-off-by: Shailend Chand <shailend@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Jeroen de Borst <jeroendb@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240122182632.1102721-3-shailend@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

gve: XDP support GQI-QPL: helper function changes

This patch adds/modifies helper functions needed to add XDP
support.

Signed-off-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Jeroen de Borst <jeroendb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gve: Reduce alloc and copy costs in the GQ rx path

Previously, even if just one of the many fragments of a 9k packet
required a copy, we'd copy the whole packet into a freshly-allocated
9k-sized linear SKB, and this led to performance issues.

By having a pool of pages to copy into, each fragment can be
independently handled, leading to a reduced incidence of
allocation and copy.

Signed-off-by: Shailend Chand <shailend@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gve: fix for null pointer dereference.

Avoid passing NULL skb to __skb_put() function call if
napi_alloc_skb() returns NULL.

Fixes: 37149e9374bf ("gve: Implement packet continuation for RX.")
Signed-off-by: Ameer Hamza <amhamza.mgc@gmail.com>
Link: https://lore.kernel.org/r/20211205183810.8299-1-amhamza.mgc@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

gve: Implement packet continuation for RX.

This enables the driver to receive RX packets spread across multiple
buffers:

For a given multi-fragment packet the "packet continuation" bit is set
on all descriptors except the last one. These descriptors' payloads are
combined into a single SKB before the SKB is handed to the
networking stack.

This change adds a "packet buffer size" notion for RX queues. The
CreateRxQueue AdminQueue command sent to the device now includes the
packet_buffer_size.

We opt for a packet_buffer_size of PAGE_SIZE / 2 to give the
driver the opportunity to flip pages where we can instead of copying.

Signed-off-by: David Awogbemila <awogbemila@google.com>
Signed-off-by: Jeroen de Borst <jeroendb@google.com>
Reviewed-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gve: Add netif_set_xps_queue call

Configure XPS when adding tx queues to the notification blocks.

Fixes: dbdaa67540512 ("gve: Move some static functions to a common file")
Signed-off-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David Awogbemila <awogbemila@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gve: DQO: Add RX path

The RX queue has an array of `gve_rx_buf_state_dqo` objects. All
allocated pages have an associated buf_state object. When a buffer is
posted on the RX buffer queue, the buffer ID will be the buf_state's
index into the RX queue's array.

On packet reception, the RX queue will have one descriptor for each
buffer associated with a received packet. Each RX descriptor will have
a buffer_id that was posted on the buffer queue.

Notable mentions:

- We use a default buffer size of 2048 bytes. Based on page size, we
may post separate sections of a single page as separate buffers.

- The driver holds an extra reference on pages passed up the receive
path with an skb and keeps these pages on a list. When posting new
buffers to the NIC, we check if any of these pages has only our
reference, or another buffer sized segment of the page has no
references. If so, it is free to reuse. This page recycling approach
is a common netdev optimization that reduces page alloc/free calls.

- Pages in the free list have a page_count bias in order to avoid an
atomic increment of pagecount every time we attempt to reuse a page.
# references = page_count() - bias

- In order to track when a page is safe to reuse, we keep track of the
last offset which had a single SKB reference. When this occurs, it
implies that every single other offset is reusable. Otherwise, we
don't know if offsets can be safely reused.

- We maintain two free lists of pages. List #1 (recycled_buf_states)
contains pages we know can be reused right away. List #2
(used_buf_states) contains pages which cannot be used right away. We
only attempt to get pages from list #2 when list #1 is empty. We only
attempt to use a small fixed number pages from list #2 before giving
up and allocating a new page. Both lists are FIFOs in hope that by the
time we attempt to reuse a page, the references were dropped.

Signed-off-by: Bailey Forrest <bcf@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gve: Make gve_rx_slot_page_info.page_offset an absolute offset

Using `page_offset` like a boolean means a page may only be split into
two sections. With page sizes larger than 4k, this can be very wasteful.
Future commits in this patchset use `struct gve_rx_slot_page_info` in a
way which supports a fixed buffer size and a variable page size.

Signed-off-by: Bailey Forrest <bcf@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gve: gve_rx_copy: Move padding to an argument

Future use cases will have a different padding value.

Signed-off-by: Bailey Forrest <bcf@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

gve: Move some static functions to a common file

These functions will be shared by the GQI and DQO variants of the GVNIC
driver as of follow-up patches in this series.

Signed-off-by: Bailey Forrest <bcf@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>