OpenGrok

/*	$NetBSD: gdt.c,v 1.48 2022/08/20 23:48:50 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.
 */

/*
 * Modified to deal with variable-length entries for NetBSD/x86_64 by
 * fvdl (at) wasabisystems.com, may 2001
 * XXX this file should be shared with the i386 code, the difference
 * can be hidden in macros.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: gdt.c,v 1.48 2022/08/20 23:48:50 riastradh Exp $");

#include "opt_multiprocessor.h"
#include "opt_xen.h"
#include "opt_user_ldt.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>

#ifdef XENPV
#include <xen/hypervisor.h>
#endif

#define NSLOTS(sz)	\
	(((sz) - DYNSEL_START) / sizeof(struct sys_segment_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;

#if defined(USER_LDT) || !defined(XENPV)
static void set_sys_gdt(int, void *, size_t, int, int, int);
#endif

void
update_descriptor(void *tp, void *ep)
{
	uint64_t *table, *entry;

	table = tp;
	entry = ep;

#ifndef XENPV
	*table = *entry;
#else
	paddr_t pa;

	if (!pmap_extract_ma(pmap_kernel(), (vaddr_t)table, &pa) ||
	    HYPERVISOR_update_descriptor(pa, *entry))
		panic("HYPERVISOR_update_descriptor failed");
#endif
}

#if defined(USER_LDT) || !defined(XENPV)
/*
 * Called on a newly-allocated GDT slot, so no race between CPUs.
 */
static void
set_sys_gdt(int slot, void *base, size_t limit, int type, int dpl, int gran)
{
	union {
		struct sys_segment_descriptor sd;
		uint64_t bits[2];
	} d;
	CPU_INFO_ITERATOR cii;
	struct cpu_info *ci;
	int idx;

	set_sys_segment(&d.sd, base, limit, type, dpl, gran);
	idx = IDXSEL(GDYNSEL(slot, SEL_KPL));
	for (CPU_INFO_FOREACH(cii, ci)) {
		KASSERT(ci->ci_gdt != NULL);
		update_descriptor(&ci->ci_gdt[idx + 0], &d.bits[0]);
		update_descriptor(&ci->ci_gdt[idx + 1], &d.bits[1]);
	}
}
#endif	/* USER_LDT || !XENPV */

/*
 * Initialize the GDT. We already have a gdtstore, which was temporarily used
 * by the bootstrap code. Now, we allocate a new gdtstore, and put it in cpu0.
 */
void
gdt_init(void)
{
	char *old_gdt;
	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;

#ifdef __HAVE_PCPU_AREA
	/* The GDT is part of the pcpuarea */
	gdtstore = (char *)&pcpuarea->ent[cpu_index(ci)].gdt;
#else
	struct vm_page *pg;
	vaddr_t va;

	/* Allocate gdt_size bytes of memory. */
	gdtstore = (char *)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());
#endif

	/* Copy the initial bootstrap GDT into the new area. */
	memcpy(gdtstore, old_gdt, DYNSEL_START);
	ci->ci_gdt = (void *)gdtstore;
#ifndef XENPV
	set_sys_segment(GDT_ADDR_SYS(gdtstore, GLDT_SEL), ldtstore,
	    LDT_SIZE - 1, SDT_SYSLDT, SEL_KPL, 0);
#endif

	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)
{
#ifdef __HAVE_PCPU_AREA
	ci->ci_gdt = (union descriptor *)&pcpuarea->ent[cpu_index(ci)].gdt;
#else
	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());
#endif

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

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

	KASSERT(curcpu() == ci);

	setregion(&region, ci->ci_gdt, (uint16_t)(gdt_size - 1));
	lgdt(&region);
}

#if !defined(XENPV) || defined(USER_LDT)
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;
}
#endif

int
tss_alloc(struct x86_64_tss *tss)
{
#ifndef XENPV
	int slot;

	mutex_enter(&cpu_lock);

	slot = gdt_get_slot();
	set_sys_gdt(slot, tss, sizeof(struct x86_64_tss) - 1, SDT_SYS386TSS,
	    SEL_KPL, 0);

	mutex_exit(&cpu_lock);

	return GDYNSEL(slot, SEL_KPL);
#else
	/* TSS, what for? */
	return GSEL(GNULL_SEL, SEL_KPL);
#endif
}

void
tss_free(int sel)
{
#ifndef XENPV
	mutex_enter(&cpu_lock);
	gdt_put_slot(IDXDYNSEL(sel));
	mutex_exit(&cpu_lock);
#else
	KASSERT(sel == GSEL(GNULL_SEL, SEL_KPL));
#endif
}

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

	KASSERT(mutex_owned(&cpu_lock));

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

	return GDYNSEL(slot, SEL_KPL);
}

void
ldt_free(int sel)
{
	int slot;

	KASSERT(mutex_owned(&cpu_lock));

	slot = IDXDYNSEL(sel);

	gdt_put_slot(slot);
}
#endif

#ifdef XENPV
void
lgdt(struct region_descriptor *desc)
{
	paddr_t frames[16];
	size_t i;
	vaddr_t va;

	/*
	 * Xen even checks descriptors AFTER limit. Zero out last frame after
	 * limit if needed.
	 */
	va = desc->rd_base + desc->rd_limit + 1;
	memset((void *)va, 0, roundup(va, PAGE_SIZE) - va);

	/*
	 * The lgdt instruction uses virtual addresses, do some translation for
	 * Xen. Mark pages R/O too, otherwise Xen will refuse to use them.
	 */
	for (i = 0; i < roundup(desc->rd_limit, PAGE_SIZE) >> PAGE_SHIFT; i++) {
		va = desc->rd_base + (i << PAGE_SHIFT);
		frames[i] = ((paddr_t)xpmap_ptetomach((pt_entry_t *)va)) >>
		    PAGE_SHIFT;
		pmap_pte_clearbits(kvtopte(va), PTE_W);
	}

	if (HYPERVISOR_set_gdt(frames, (desc->rd_limit + 1) >> 3))
		panic("lgdt(): HYPERVISOR_set_gdt() failed");
	lgdt_finish();
}
#endif