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Kernel/aarch64: Add implementation of Processor::switch_context

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This initial implementation makes it possible to actually context switch
between different kernel threads! :^)
This commit is contained in:
Timon Kruiper 2022-12-27 21:13:31 +01:00 • committed by Andrew Kaster
parent 0b95d8cd24
commit a5e98d3644
2 changed files with 107 additions and 5 deletions
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106
Kernel/Arch/aarch64/Processor.cpp
View file

@ -25,6 +25,7 @@ namespace Kernel {
extern "C" void thread_context_first_enter(void);
extern "C" void exit_kernel_thread(void);
extern "C" void context_first_init(Thread* from_thread, Thread* to_thread) __attribute__((used));
extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread) __attribute__((used));
Processor* g_current_processor;
@ -112,9 +113,94 @@ void Processor::initialize_context_switching(Thread& initial_thread)
void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
{
(void)from_thread;
(void)to_thread;
TODO_AARCH64();
VERIFY(!m_in_irq);
VERIFY(m_in_critical == 1);
dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context --> switching out of: {} {}", VirtualAddress(from_thread), *from_thread);
// m_in_critical is restored in enter_thread_context
from_thread->save_critical(m_in_critical);
// clang-format off
asm volatile(
"sub sp, sp, #248 \n"
"stp x0, x1, [sp, #(0 * 0)] \n"
"stp x2, x3, [sp, #(2 * 8)] \n"
"stp x4, x5, [sp, #(4 * 8)] \n"
"stp x6, x7, [sp, #(6 * 8)] \n"
"stp x8, x9, [sp, #(8 * 8)] \n"
"stp x10, x11, [sp, #(10 * 8)] \n"
"stp x12, x13, [sp, #(12 * 8)] \n"
"stp x14, x15, [sp, #(14 * 8)] \n"
"stp x16, x17, [sp, #(16 * 8)] \n"
"stp x18, x19, [sp, #(18 * 8)] \n"
"stp x20, x21, [sp, #(20 * 8)] \n"
"stp x22, x23, [sp, #(22 * 8)] \n"
"stp x24, x25, [sp, #(24 * 8)] \n"
"stp x26, x27, [sp, #(26 * 8)] \n"
"stp x28, x29, [sp, #(28 * 8)] \n"
"str x30, [sp, #(30 * 8)] \n"
"mov x0, sp \n"
"str x0, %[from_sp] \n"
"ldr x0, =1f \n"
"str x0, %[from_ip] \n"
"ldr x0, %[to_sp] \n"
"mov sp, x0 \n"
"sub sp, sp, 24 \n"
"ldr x0, %[from_thread] \n"
"ldr x1, %[to_thread] \n"
"ldr x2, %[to_ip] \n"
"str x0, [sp, #0] \n"
"str x1, [sp, #8] \n"
"str x2, [sp, #16] \n"
"bl enter_thread_context \n"
"ldr x0, [sp, #16]\n"
"br x0 \n"
"1: \n"
"add sp, sp, 24 \n"
"ldp x0, x1, [sp, #(0 * 0)] \n"
"ldp x2, x3, [sp, #(2 * 8)] \n"
"ldp x4, x5, [sp, #(4 * 8)] \n"
"ldp x6, x7, [sp, #(6 * 8)] \n"
"ldp x8, x9, [sp, #(8 * 8)] \n"
"ldp x10, x11, [sp, #(10 * 8)] \n"
"ldp x12, x13, [sp, #(12 * 8)] \n"
"ldp x14, x15, [sp, #(14 * 8)] \n"
"ldp x16, x17, [sp, #(16 * 8)] \n"
"ldp x18, x19, [sp, #(18 * 8)] \n"
"ldp x20, x21, [sp, #(20 * 8)] \n"
"ldp x22, x23, [sp, #(22 * 8)] \n"
"ldp x24, x25, [sp, #(24 * 8)] \n"
"ldp x26, x27, [sp, #(26 * 8)] \n"
"ldp x28, x29, [sp, #(28 * 8)] \n"
"ldr x30, [sp, #(30 * 8)] \n"
"sub sp, sp, 24 \n"
"ldr x0, [sp, #0] \n"
"ldr x1, [sp, #8] \n"
"str x0, %[from_thread] \n"
"str x1, %[to_thread] \n"
"add sp, sp, #272 \n"
:
[from_ip] "=m"(from_thread->regs().elr_el1),
[from_sp] "=m"(from_thread->regs().sp_el0),
"=m"(from_thread),
"=m"(to_thread)
: [to_ip] "m"(to_thread->regs().elr_el1),
[to_sp] "m"(to_thread->regs().sp_el0),
[from_thread] "m"(from_thread),
[to_thread] "m"(to_thread)
: "memory", "x0", "x1", "x2");
// clang-format on
dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context <-- from {} {} to {} {}", VirtualAddress(from_thread), *from_thread, VirtualAddress(to_thread), *to_thread);
}
void Processor::assume_context(Thread& thread, FlatPtr flags)
@ -315,4 +401,18 @@ extern "C" void context_first_init([[maybe_unused]] Thread* from_thread, [[maybe
Scheduler::leave_on_first_switch(InterruptsState::Disabled);
}
extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread)
{
VERIFY(from_thread == to_thread || from_thread->state() != Thread::State::Running);
VERIFY(to_thread->state() == Thread::State::Running);
Processor::set_current_thread(*to_thread);
to_thread->set_cpu(Processor::current().id());
auto in_critical = to_thread->saved_critical();
VERIFY(in_critical > 0);
Processor::restore_critical(in_critical);
}
}

6
Kernel/Arch/aarch64/vector_table.S
View file

@ -60,8 +60,6 @@
str x0, [sp, #ELR_EL1_SLOT]
mrs x0, tpidr_el0
str x0, [sp, #TPIDR_EL0_SLOT]
mrs x0, sp_el0
str x0, [sp, #SP_EL0_SLOT]
// Set up TrapFrame struct on the stack
sub sp, sp, #16
@ -168,6 +166,10 @@ synchronous_current_elsp_el0:
eret
irq_current_elsp_el0:
// An IRQ will always switch the stack pointer to SP_EL1, however we want to use SP_EL0, so switch
// to SP_EL0. This means that the stack of the currently executing thread is used as the irq stack.
msr SPSel, #0
save_current_context
bl handle_interrupt
restore_previous_context