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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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29
Kernel/VirtIO/VirtIORNG.cpp
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@ -23,7 +23,7 @@ VirtIORNG::VirtIORNG(PCI::Address address)
m_entropy_buffer = MM.allocate_contiguous_kernel_region(PAGE_SIZE, "VirtIORNG", Region::Access::Read | Region::Access::Write);
if (m_entropy_buffer) {
memset(m_entropy_buffer->vaddr().as_ptr(), 0, m_entropy_buffer->size());
supply_buffer_and_notify(REQUESTQ, ScatterGatherRefList::create_from_physical(m_entropy_buffer->physical_page(0)->paddr(), m_entropy_buffer->size()), BufferType::DeviceWritable, m_entropy_buffer->vaddr().as_ptr());
request_entropy_from_host();
}
}
}
@ -40,14 +40,33 @@ bool VirtIORNG::handle_device_config_change()
void VirtIORNG::handle_queue_update(u16 queue_index)
{
VERIFY(queue_index == REQUESTQ);
size_t available_entropy = 0;
if (!get_queue(REQUESTQ).get_buffer(&available_entropy))
return;
size_t available_entropy = 0, used;
auto& queue = get_queue(REQUESTQ);
{
ScopedSpinLock lock(queue.lock());
auto chain = queue.pop_used_buffer_chain(used);
if (chain.is_empty())
return;
VERIFY(chain.length() == 1);
chain.for_each([&available_entropy](PhysicalAddress, size_t length) {
available_entropy = length;
});
chain.release_buffer_slots_to_queue();
}
dbgln_if(VIRTIO_DEBUG, "VirtIORNG: received {} bytes of entropy!", available_entropy);
for (auto i = 0u; i < available_entropy; i++) {
m_entropy_source.add_random_event(m_entropy_buffer->vaddr().as_ptr()[i]);
}
// TODO: when should we ask for more entropy from the host?
// TODO: When should we get some more entropy?
}
void VirtIORNG::request_entropy_from_host()
{
auto& queue = get_queue(REQUESTQ);
ScopedSpinLock lock(queue.lock());
VirtIOQueueChain chain(queue);
chain.add_buffer_to_chain(m_entropy_buffer->physical_page(0)->paddr(), PAGE_SIZE, BufferType::DeviceWritable);
supply_chain_and_notify(REQUESTQ, chain);
}
}