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Kernel: Switch processor to EL1 immediately after boot on Aarch64

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This commit is contained in:
Marcin Undak 2021-10-08 17:07:24 -04:00 • committed by Linus Groh
parent d6021300d5
commit 2d9fa8146c
4 changed files with 321 additions and 16 deletions
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135
Kernel/Prekernel/Arch/aarch64/init.cpp
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@ -12,8 +12,14 @@
#include <Kernel/Prekernel/Arch/aarch64/UART.h>
extern "C" [[noreturn]] void halt();
extern "C" [[noreturn]] void init();
extern "C" [[noreturn]] void os_start();
static void set_up_el1_mode();
static void set_up_el2_mode();
static void set_up_el3_mode();
[[noreturn]] static void switch_to_el1();
extern "C" [[noreturn]] void init()
{
auto& uart = Prekernel::UART::the();
@ -27,22 +33,11 @@ extern "C" [[noreturn]] void init()
uart.print_num(firmware_version);
uart.print_str("\r\n");
auto exception_level = get_current_exception_level();
uart.print_str("Current CPU exception level: EL");
uart.print_num(exception_level);
uart.print_str("\r\n");
set_up_el3_mode();
set_up_el2_mode();
set_up_el1_mode();
auto& timer = Prekernel::Timer::the();
u64 start_musec = 0;
for (;;) {
u64 now_musec;
while ((now_musec = timer.microseconds_since_boot()) - start_musec < 1'000'000)
;
start_musec = now_musec;
uart.print_str("Timer: ");
uart.print_num(now_musec);
uart.print_str("\r\n");
}
switch_to_el1();
}
// FIXME: Share this with the Intel Prekernel.
@ -66,3 +61,111 @@ void __stack_chk_fail()
{
halt();
}
static void set_up_el1_mode()
{
Kernel::Aarch64_SCTLR_EL1 sctlr_el1 = {};
// Those bits are reserved on ARMv8.0
sctlr_el1.LSMAOE = 1;
sctlr_el1.nTLSMD = 1;
sctlr_el1.SPAN = 1;
sctlr_el1.IESB = 1;
// Don't trap access to CTR_EL0
sctlr_el1.UCT = 1;
// Don't trap WFE instructions
sctlr_el1.nTWE = 1;
// Don't trap WFI instructions
sctlr_el1.nTWI = 1;
// Don't trap DC ZVA instructions
sctlr_el1.DZE = 1;
// Don't trap access to DAIF (debugging) flags of EFLAGS register
sctlr_el1.UMA = 1;
// Enable stack access alignment check for EL0
sctlr_el1.SA0 = 1;
// Enable stack access alignment check for EL1
sctlr_el1.SA = 1;
// Enable memory access alignment check
sctlr_el1.A = 1;
// Set the register
asm("msr sctlr_el1, %[value]" ::[value] "r"(sctlr_el1));
}
static void set_up_el2_mode()
{
Kernel::Aarch64_HCR_EL2 hcr_el2 = {};
// EL1 to use 64-bit mode
hcr_el2.RW = 1;
// Set the register
asm("msr hcr_el2, %[value]" ::[value] "r"(hcr_el2));
}
static void set_up_el3_mode()
{
Kernel::Aarch64_SCR_EL3 scr_el3 = {};
// Don't trap access to Counter-timer Physical Secure registers
scr_el3.ST = 1;
// Lower level to use Aarch64
scr_el3.RW = 1;
// Enable Hypervisor instructions at all levels
scr_el3.HCE = 1;
// Set the register
asm("msr scr_el3, %[value]" ::[value] "r"(scr_el3));
}
[[noreturn]] static void switch_to_el1()
{
// Processor state to set when returned from this function (in new EL1 world)
Kernel::Aarch64_SPSR_EL3 spsr_el3 = {};
// Mask (disable) all interrupts
spsr_el3.A = 1;
spsr_el3.I = 1;
spsr_el3.F = 1;
// Indicate EL1 as exception origin mode (so we go back there)
spsr_el3.M = Kernel::Aarch64_SPSR_EL3::Mode::EL1h;
// Set the register
asm("msr spsr_el3, %[value]" ::[value] "r"(spsr_el3));
// This will jump into os_start() below, but in EL1
return_from_el3();
}
extern "C" [[noreturn]] void os_start()
{
auto& uart = Prekernel::UART::the();
auto exception_level = get_current_exception_level();
uart.print_str("Current CPU exception level: EL");
uart.print_num(exception_level);
uart.print_str("\r\n");
auto& timer = Prekernel::Timer::the();
u64 start_musec = 0;
for (;;) {
u64 now_musec;
while ((now_musec = timer.microseconds_since_boot()) - start_musec < 1'000'000)
;
start_musec = now_musec;
uart.print_str("Timer: ");
uart.print_num(now_musec);
uart.print_str("\r\n");
}
}