universalisos/kernel/arch/arm/uos_adspace.cpp

/*
 * Universalisos per-VM address-space management — implementation
 *
 * Faithful port of PikeOS arch/arm/src/adspace.c (148 lines), `uos_` naming.
 * Only PikeOS-isms removed: sched_preempt_point() -> no-op, assert() -> check,
 * KERN_TO_PHYS/TTB_FLAGS from uos_armmmu_v6.h + uos_adspace.h.
 *
 * Author: PortugalFuturista Hypervisor Development Team (adapted from SYSGO PikeOS)
 */

#include "uos_adspace.h"

/* PikeOS calls sched_preempt_point() in a few spots; until the D-3 scheduler
 * tick exists this is a no-op. */
static inline void uos_preempt_point(void) { }

/**
 * Switch current address space (PikeOS p4arch_adspace_set_active).
 *
 * Sequence: DSB (Errata 754322) -> ASID 0 (neutral during switch) -> new
 * TTBR0 (physical base of the task's user pgdir) -> invalidate BTAC ->
 * DSB -> set the task's ASID to tag new TLB entries.
 */
void uos_arch_adspace_set_active(uos_taskinfo_t *td, uos_taskinfo_t *prev) {
    (void)prev;
    if (td == nullptr || td->adspace.pgdir == nullptr) {
        return;   /* kernel/idle task: no TTBR0 swap (stays on TTBR1) */
    }

    uos_arm_dsb();                       /* Errata 754322 */
    uos_arm_set_asid(0);
    uos_arm_set_ttbr0(UOS_KERN_TO_PHYS((uint32_t)(uintptr_t)&td->adspace.pgdir[0]) | UOS_TTB_FLAGS);
    uos_arm_inval_btac();
    uos_arm_tlb_inval_all();             /* flush stale global kernel TLB entries */
    uos_arm_dsb();                       /* Errata 754322 */
    uos_arm_set_asid(td->taskno);
}

/** Set up the address space of the idle/kernel task (runs on TTBR1 only). */
void uos_arch_adspace_register_kernel(uos_taskinfo_t *td) {
    td->adspace.pgdir = nullptr;
    uos_arch_adspace_register_user(td);
}

/** Initialise a new address space. The pgdir is assigned later (register_user). */
int uos_arch_adspace_init(uos_taskinfo_t *td) {
    td->adspace.pgdir = nullptr;
    uos_preempt_point();
    return 0;   /* UOS_E_OK */
}

/**
 * Register a new address space: assign the task's half-size user pgdir out of
 * the global pool allocated by uos_arm_init_mmu (kglobal.mach.user_pgdirs).
 */
void uos_arch_adspace_register_user(uos_taskinfo_t *td) {
    uos_task_mmuctxt_t *adspace = &td->adspace;

    /* PikeOS: assert(adspace->pgdir == NULL); */
    if (adspace->pgdir != nullptr) {
        return;   /* already registered */
    }
    /* TTBCR=0: TTBR0 covers all 4 GB, so each guest pgdir is full-size
     * (4096 entries = 16 KiB), cloned from the kernel flat map. */
    adspace->pgdir = uos_user_pgdirs + td->taskno * UOS_PD_ENTRIES;
}

/** Unused callback (PikeOS leaves this empty). */
void uos_arch_adspace_free(uos_taskinfo_t *td) {
    (void)td;
}

/**
 * Unmap a task's complete user address space: walk every 4K-pgdir slot in
 * [USR_BASE, USR_END), free any L2 page table behind it, then flush the task's
 * ASID-tagged TLB entries.
 */
void uos_arch_adspace_unmap_user(uos_taskinfo_t *td) {
    uos_task_mmuctxt_t *adspace = &td->adspace;
    uint32_t vaddr = UOS_MEM_USR_BASE;

    while (vaddr < UOS_MEM_USR_END) {
        uos_preempt_point();
        if (adspace->pgdir != nullptr) {
            uint32_t pdent = adspace->pgdir[UOS_PD_INDEX_4K(vaddr)];
            if ((pdent & UOS_PD_PT) != 0u) {
                uos_arm_free_pt(td, vaddr);   /* free the L2 table */
            }
        }
        vaddr += UOS_PT_ENTRIES_4K * UOS_PAGESIZE;
    }

    uos_arm_tlb_inval_asid(td->taskno);
}