/*      $NetBSD: gdt.c,v 1.74 2023/07/16 19:55:43 riastradh Exp $       */

/*
 * Copyright (c) 1996, 1997, 2009 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by John T. Kohl, by Charles M. Hannum, and by Andrew Doran.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: gdt.c,v 1.74 2023/07/16 19:55:43 riastradh Exp $");

#include "opt_multiprocessor.h"
#include "opt_xen.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/mutex.h>
#include <sys/cpu.h>

#include <uvm/uvm.h>

#include <machine/gdt.h>
#include <machine/pmap_private.h>

#define NSLOTS(sz)      \
        (((sz) - DYNSEL_START) / sizeof(union descriptor))
#define NDYNSLOTS       NSLOTS(MAXGDTSIZ)

typedef struct {
        bool busy[NDYNSLOTS];
        size_t nslots;
} gdt_bitmap_t;

/* size of GDT in bytes */
#ifdef XENPV
const size_t gdt_size = FIRST_RESERVED_GDT_BYTE;
#else
const size_t gdt_size = MAXGDTSIZ;
#endif

/* bitmap of busy slots */
static gdt_bitmap_t gdt_bitmap;

#ifndef XENPV
static int ldt_count;   /* number of LDTs */
static int ldt_max = 1000;/* max number of LDTs */
static void setgdt(int, const void *, size_t, int, int, int, int);
static int gdt_get_slot(void);
static void gdt_put_slot(int);
#endif
void gdt_init(void);

void
update_descriptor(union descriptor *table, union descriptor *entry)
{
#ifndef XENPV
        *table = *entry;
#else
        paddr_t pa;
        pt_entry_t *ptp;

        ptp = kvtopte((vaddr_t)table);
        pa = (*ptp & PTE_4KFRAME) | ((vaddr_t)table & ~PTE_4KFRAME);
        if (HYPERVISOR_update_descriptor(pa, entry->raw[0], entry->raw[1]))
                panic("HYPERVISOR_update_descriptor failed\n");
#endif
}

#ifndef XENPV
/*
 * Called on a newly-allocated GDT slot, so no race between CPUs.
 */
static void
setgdt(int slot, const void *base, size_t limit, int type, int dpl, int def32,
    int gran)
{
        struct segment_descriptor *sd;
        CPU_INFO_ITERATOR cii;
        struct cpu_info *ci;
        int idx;

        idx = IDXSEL(GDYNSEL(slot, SEL_KPL));
        sd = &gdtstore[idx].sd;
        setsegment(sd, base, limit, type, dpl, def32, gran);
        for (CPU_INFO_FOREACH(cii, ci)) {
                if (ci->ci_gdt != NULL)
                        update_descriptor(&ci->ci_gdt[idx],
                            (union descriptor *)sd);
        }
}
#endif

/*
 * gdt_init()
 *
 *      Create a permanent Global Descriptor Table (GDT) for the
 *      primary CPU.  This replaces the second tepmorary GDT that was
 *      allocated in pmap_bootstrap with pmap_bootstrap_valloc and
 *      pmap_bootstrap_palloc -- which in turn replaced the initial
 *      temporary GDT allocated on the stack early at boot and
 *      initialized with initgdt.
 *
 *      1. Allocate permanent space for the primary CPU's GDT with
 *         uvm_km(9).
 *
 *      2. Copy the temporary GDT's contents over.  See initgdt for the
 *         original initialization; it was copied from the initial
 *         temporary GDT to the second temporary GDT in init386.
 *
 *      3. Make sure the GCPU_SEL segment descriptor points to
 *         &cpu_info_primary.
 *
 *         XXX Is this necessary?  It appears to be redundant with
 *         initgdt.
 *
 *      4. Load the permanent GDT address into the Global Descriptor
 *         Table Register (GDTR) with LGDT (via gdt_init_cpu).
 */
void
gdt_init(void)
{
        union descriptor *old_gdt;
        struct vm_page *pg;
        vaddr_t va;
        struct cpu_info *ci = &cpu_info_primary;

        /* Initialize the global values */
        memset(&gdt_bitmap.busy, 0, sizeof(gdt_bitmap.busy));
        gdt_bitmap.nslots = NSLOTS(gdt_size);

        old_gdt = gdtstore;

        /* Allocate gdt_size bytes of memory. */
        gdtstore = (union descriptor *)uvm_km_alloc(kernel_map, gdt_size, 0,
            UVM_KMF_VAONLY);
        for (va = (vaddr_t)gdtstore; va < (vaddr_t)gdtstore + gdt_size;
            va += PAGE_SIZE) {
                pg = uvm_pagealloc(NULL, 0, NULL, UVM_PGA_ZERO);
                if (pg == NULL) {
                        panic("gdt_init: no pages");
                }
                pmap_kenter_pa(va, VM_PAGE_TO_PHYS(pg),
                    VM_PROT_READ | VM_PROT_WRITE, 0);
        }
        pmap_update(pmap_kernel());

        /* Copy the initial bootstrap GDT into the new area. */
        memcpy(gdtstore, old_gdt, NGDT * sizeof(gdtstore[0]));
        ci->ci_gdt = gdtstore;
        setsegment(&ci->ci_gdt[GCPU_SEL].sd, ci,
            sizeof(struct cpu_info) - 1, SDT_MEMRWA, SEL_KPL, 1, 0);

        gdt_init_cpu(ci);
}

/*
 * Allocate shadow GDT for a secondary CPU. It contains the same values as the
 * GDT present in cpu0 (gdtstore).
 */
void
gdt_alloc_cpu(struct cpu_info *ci)
{
        struct vm_page *pg;
        vaddr_t va;

        ci->ci_gdt = (union descriptor *)uvm_km_alloc(kernel_map, gdt_size,
            0, UVM_KMF_VAONLY);
        for (va = (vaddr_t)ci->ci_gdt; va < (vaddr_t)ci->ci_gdt + gdt_size;
            va += PAGE_SIZE) {
                while ((pg = uvm_pagealloc(NULL, 0, NULL, UVM_PGA_ZERO))
                    == NULL) {
                        uvm_wait("gdt_alloc_cpu");
                }
                pmap_kenter_pa(va, VM_PAGE_TO_PHYS(pg),
                    VM_PROT_READ | VM_PROT_WRITE, 0);
        }
        pmap_update(pmap_kernel());

        memcpy(ci->ci_gdt, gdtstore, gdt_size);

        setsegment(&ci->ci_gdt[GCPU_SEL].sd, ci,
            sizeof(struct cpu_info) - 1, SDT_MEMRWA, SEL_KPL, 1, 0);
}

/*
 * Load appropriate GDT descriptor into the currently running CPU, which must
 * be ci.
 */
void
gdt_init_cpu(struct cpu_info *ci)
{
#ifndef XENPV
        struct region_descriptor region;

        setregion(&region, ci->ci_gdt, gdt_size - 1);
        lgdt(&region);
#else
        size_t len = roundup(gdt_size, PAGE_SIZE);
        unsigned long frames[len >> PAGE_SHIFT];
        vaddr_t va;
        pt_entry_t *ptp;
        size_t f;

        for (va = (vaddr_t)ci->ci_gdt, f = 0;
            va < (vaddr_t)ci->ci_gdt + gdt_size;
            va += PAGE_SIZE, f++) {
                KASSERT(va >= VM_MIN_KERNEL_ADDRESS);
                ptp = kvtopte(va);
                frames[f] = *ptp >> PAGE_SHIFT;

                /* 
                 * Our own
                 *      pmap_pte_clearbits(ptp, PTE_W)
                 * but without spl(), since %fs is not set up properly yet; ie
                 * curcpu() won't work at this point and spl() will break.
                 */
                if (HYPERVISOR_update_va_mapping((vaddr_t)va,
                    *ptp & ~PTE_W, UVMF_INVLPG) < 0) {
                        panic("%s page RO update failed.\n", __func__);
                }
        }

        if (HYPERVISOR_set_gdt(frames, gdt_size / sizeof(gdtstore[0])))
                panic("HYPERVISOR_set_gdt failed!\n");
        lgdt_finish();
#endif
}

#ifndef XENPV
static int
gdt_get_slot(void)
{
        size_t i;

        KASSERT(mutex_owned(&cpu_lock));

        for (i = 0; i < gdt_bitmap.nslots; i++) {
                if (!gdt_bitmap.busy[i]) {
                        gdt_bitmap.busy[i] = true;
                        return (int)i;
                }
        }
        panic("gdt_get_slot: out of memory");

        /* NOTREACHED */
        return 0;
}

static void
gdt_put_slot(int slot)
{
        KASSERT(mutex_owned(&cpu_lock));
        KASSERT(slot < gdt_bitmap.nslots);
        gdt_bitmap.busy[slot] = false;
}

int
tss_alloc(const struct i386tss *tss)
{
        int slot;

        mutex_enter(&cpu_lock);
        slot = gdt_get_slot();
        setgdt(slot, tss, sizeof(struct i386tss) + IOMAPSIZE - 1,
            SDT_SYS386TSS, SEL_KPL, 0, 0);
        mutex_exit(&cpu_lock);

        return GDYNSEL(slot, SEL_KPL);
}

void
tss_free(int sel)
{

        mutex_enter(&cpu_lock);
        gdt_put_slot(IDXDYNSEL(sel));
        mutex_exit(&cpu_lock);
}

int
ldt_alloc(void *ldtp, size_t len)
{
        int slot;

        KASSERT(mutex_owned(&cpu_lock));

        if (ldt_count >= ldt_max) {
                return -1;
        }
        ldt_count++;

        slot = gdt_get_slot();
        setgdt(slot, ldtp, len - 1, SDT_SYSLDT, SEL_KPL, 0, 0);

        return GDYNSEL(slot, SEL_KPL);
}

void
ldt_free(int sel)
{
        int slot;

        KASSERT(mutex_owned(&cpu_lock));
        KASSERT(ldt_count > 0);

        slot = IDXDYNSEL(sel);
        gdt_put_slot(slot);
        ldt_count--;
}
#endif