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https://github.com/Mathewnd/Astral.git
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Matheus
109 lines
3.0 KiB
C
109 lines
3.0 KiB
C
#include <arch/ldt.h>
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#include <arch/gdt.h>
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#include <kernel/alloc.h>
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#include <errno.h>
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#include <arch/cpu.h>
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#include <arch/smp.h>
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#include <spinlock.h>
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static spinlock_t ldt_invalidate_lock;
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static size_t done;
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#define LDT_ENTRIES 8192
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#define LDT_ENTRY_ACCESS_BYTE(entry) (((entry) >> 40) & 0xff)
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#define LDT_ENTRY_FLAGS(entry) (((entry) >> 52) & 0xf)
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#define LDT_ENTRY_CODE 0x08
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#define LDT_ENTRY_S 0x10
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#define LDT_ENTRY_DPL_MASK 0x60
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#define LDT_ENTRY_DPL_USER 0x60
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#define LDT_ENTRY_PRESENT 0x80
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#define LDT_ENTRY_LONG 0x2
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#define LDT_ENTRY_DB 0x4
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void arch_ldt_invalidate(void) {
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arch_gdt_set_ldt(current_thread()->proc->ldt, 0xffff);
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__atomic_add_fetch(&done, 1, __ATOMIC_SEQ_CST);
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}
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int arch_ldt_set_entry(unsigned int which, ldt_entry_t entry) {
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if (which >= LDT_ENTRIES)
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return EINVAL;
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if (entry != 0) {
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uint8_t access = LDT_ENTRY_ACCESS_BYTE(entry);
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uint8_t flags = LDT_ENTRY_FLAGS(entry);
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if ((access & LDT_ENTRY_S) == 0)
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return EINVAL;
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if ((access & LDT_ENTRY_DPL_MASK) != LDT_ENTRY_DPL_USER)
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return EINVAL;
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if ((access & LDT_ENTRY_PRESENT) == 0)
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return EINVAL;
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if ((access & LDT_ENTRY_CODE) == 0) {
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if (flags & LDT_ENTRY_LONG)
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return EINVAL;
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} else if ((flags & (LDT_ENTRY_LONG | LDT_ENTRY_DB)) == (LDT_ENTRY_LONG | LDT_ENTRY_DB)) {
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return EINVAL;
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}
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}
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if (__atomic_load_n(¤t_thread()->proc->ldt, __ATOMIC_RELAXED) == NULL) {
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ldt_entry_t *ldt = alloc(sizeof(ldt_entry_t) * LDT_ENTRIES);
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if (ldt == NULL)
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return ENOMEM;
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ldt_entry_t *expected = NULL;
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bool swap_ok = __atomic_compare_exchange_n(¤t_thread()->proc->ldt, &expected, ldt, false, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED);
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if (!swap_ok)
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free(ldt);
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bool do_shootdown = // do shootdown if
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swap_ok // we actually need to
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&& arch_smp_cpusawake >= 2 // there are multiple cpus in the system
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&& current_thread()->proc->runningthreadcount > 1; // in a process which has multiple threads running
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if (do_shootdown) {
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long old_ipl = spinlock_acquire_raise_ipl(&ldt_invalidate_lock, IPL_DPC);
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size_t shootdown_total = 1;
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done = 0;
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for (int i = 0; i < arch_smp_cpusawake; ++i) {
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// reading the mm context like this is racey but there are no ill side effects other than spurious shootdowns
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// if a cpu changes to this mmctx, they will already have done a ldt invalidation.
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// if it changes out of it, same thing
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if (smp_cpus[i] == current_cpu() || (smp_cpus[i]->mmctx != current_thread()->mmctx))
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continue;
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++shootdown_total;
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arch_smp_send_ipi(smp_cpus[i], &smp_cpus[i]->isr[0xfc], ARCH_SMP_IPI_TARGET, false);
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}
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arch_ldt_invalidate();
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while (__atomic_load_n(&done, __ATOMIC_SEQ_CST) != shootdown_total) asm("pause");
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spinlock_release_lower_ipl(&ldt_invalidate_lock, old_ipl);
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}
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}
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__atomic_store_n(¤t_thread()->proc->ldt[which], entry, __ATOMIC_RELAXED);
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return 0;
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}
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int arch_ldt_fork(ldt_entry_t **dst, ldt_entry_t *src) {
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*dst = alloc(sizeof(ldt_entry_t) * LDT_ENTRIES);
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if (*dst == NULL)
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return ENOMEM;
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memcpy(*dst, src, sizeof(ldt_entry_t) * LDT_ENTRIES);
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return 0;
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}
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