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Kernel: Move VirtIO code away from using a scatter gather list

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Currently, when passing buffers into VirtIOQueues, we use scatter-gather
lists, which contain an internal vector of buffers. This vector is
allocated, filled and the destroy whenever we try to provide buffers
into a virtqueue, which would happen a lot in performance cricital code
(the main transport mechanism for certain paravirtualized devices).

This commit moves it over to using VirtIOQueueChains and building the
chain in place in the VirtIOQueue. Also included are a bunch of fixups
for the VirtIO Console device, making it use an internal VM::RingBuffer
instead.
This commit is contained in:
Sahan Fernando 2021-04-24 11:05:51 +10:00 • committed by Andreas Kling
parent 13d5cdcd08
commit ed0e7b53a5
11 changed files with 312 additions and 159 deletions
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72
Kernel/VirtIO/VirtIOConsole.cpp
View file

@ -4,7 +4,6 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <Kernel/VM/ScatterGatherList.h>
#include <Kernel/VirtIO/VirtIOConsole.h>
namespace Kernel {
@ -41,11 +40,8 @@ VirtIOConsole::VirtIOConsole(PCI::Address address)
}
if (success) {
finish_init();
m_receive_region = MM.allocate_contiguous_kernel_region(PAGE_SIZE, "VirtIOConsole Receive", Region::Access::Read | Region::Access::Write);
if (m_receive_region) {
supply_buffer_and_notify(RECEIVEQ, ScatterGatherRefList::create_from_physical(m_receive_region->physical_page(0)->paddr(), m_receive_region->size()), BufferType::DeviceWritable, m_receive_region->vaddr().as_ptr());
}
m_transmit_region = MM.allocate_contiguous_kernel_region(PAGE_SIZE, "VirtIOConsole Transmit", Region::Access::Read | Region::Access::Write);
m_receive_buffer = make<RingBuffer>("VirtIOConsole Receive", RINGBUFFER_SIZE);
m_transmit_buffer = make<RingBuffer>("VirtIOConsole Transmit", RINGBUFFER_SIZE);
}
}
}
@ -62,14 +58,31 @@ bool VirtIOConsole::handle_device_config_change()
void VirtIOConsole::handle_queue_update(u16 queue_index)
{
dbgln_if(VIRTIO_DEBUG, "VirtIOConsole: Handle queue update");
VERIFY(queue_index <= TRANSMITQ);
switch (queue_index) {
case RECEIVEQ:
case RECEIVEQ: {
ScopedSpinLock lock(get_queue(RECEIVEQ).lock());
get_queue(RECEIVEQ).discard_used_buffers(); // TODO: do something with incoming data (users writing into qemu console) instead of just clearing
break;
case TRANSMITQ:
get_queue(TRANSMITQ).discard_used_buffers(); // clear outgoing buffers that the device finished with
}
case TRANSMITQ: {
ScopedSpinLock ringbuffer_lock(m_transmit_buffer->lock());
auto& queue = get_queue(TRANSMITQ);
ScopedSpinLock queue_lock(queue.lock());
size_t used;
VirtIOQueueChain popped_chain = queue.pop_used_buffer_chain(used);
do {
popped_chain.for_each([this](PhysicalAddress address, size_t length) {
m_transmit_buffer->reclaim_space(address, length);
});
popped_chain.release_buffer_slots_to_queue();
popped_chain = queue.pop_used_buffer_chain(used);
} while (!popped_chain.is_empty());
// Unblock any IO tasks that were blocked because can_write() returned false
evaluate_block_conditions();
break;
}
default:
VERIFY_NOT_REACHED();
}
@ -77,31 +90,50 @@ void VirtIOConsole::handle_queue_update(u16 queue_index)
bool VirtIOConsole::can_read(const FileDescription&, size_t) const
{
return false;
return true;
}
KResultOr<size_t> VirtIOConsole::read(FileDescription&, u64, [[maybe_unused]] UserOrKernelBuffer& data, size_t size)
KResultOr<size_t> VirtIOConsole::read(FileDescription&, u64, [[maybe_unused]] UserOrKernelBuffer& data, size_t)
{
if (!size)
return 0;
return 1;
return ENOTSUP;
}
bool VirtIOConsole::can_write(const FileDescription&, size_t) const
{
return get_queue(TRANSMITQ).can_write();
return get_queue(TRANSMITQ).has_free_slots() && m_transmit_buffer->has_space();
}
KResultOr<size_t> VirtIOConsole::write(FileDescription&, u64, const UserOrKernelBuffer& data, size_t size)
KResultOr<size_t> VirtIOConsole::write(FileDescription& desc, u64, const UserOrKernelBuffer& data, size_t size)
{
if (!size)
return 0;
auto scatter_list = ScatterGatherRefList::create_from_buffer(static_cast<const u8*>(data.user_or_kernel_ptr()), size);
supply_buffer_and_notify(TRANSMITQ, scatter_list, BufferType::DeviceReadable, const_cast<void*>(data.user_or_kernel_ptr()));
if (!can_write(desc, size))
return EAGAIN;
return size;
ScopedSpinLock ringbuffer_lock(m_transmit_buffer->lock());
auto& queue = get_queue(TRANSMITQ);
ScopedSpinLock queue_lock(queue.lock());
VirtIOQueueChain chain(queue);
size_t total_bytes_copied = 0;
do {
PhysicalAddress start_of_chunk;
size_t length_of_chunk;
if (!m_transmit_buffer->copy_data_in(data, total_bytes_copied, size - total_bytes_copied, start_of_chunk, length_of_chunk)) {
chain.release_buffer_slots_to_queue();
return EINVAL;
}
bool did_add_buffer = chain.add_buffer_to_chain(start_of_chunk, length_of_chunk, BufferType::DeviceReadable);
VERIFY(did_add_buffer);
total_bytes_copied += length_of_chunk;
} while (total_bytes_copied < size && can_write(desc, size - total_bytes_copied));
supply_chain_and_notify(TRANSMITQ, chain);
return total_bytes_copied;
}
}