linux_kernel/arch/arm64/include/asm/mmu_context.h

/*
 * Based on arch/arm/include/asm/mmu_context.h
 *
 * Copyright (C) 1996 Russell King.
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#ifndef __ASM_MMU_CONTEXT_H
#define __ASM_MMU_CONTEXT_H

#include <linux/compiler.h>
#include <linux/sched.h>

#include <asm/cacheflush.h>
#include <asm/cpufeature.h>
#include <asm/proc-fns.h>
#include <asm-generic/mm_hooks.h>
#include <asm/cputype.h>
#include <asm/pgtable.h>
#include <asm/sysreg.h>
#include <asm/tlbflush.h>

static inline void contextidr_thread_switch(struct task_struct *next)
{
	if (!IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR))
		return;

	write_sysreg(task_pid_nr(next), contextidr_el1);
	isb();
}

/*
 * Set TTBR0 to empty_zero_page. No translations will be possible via TTBR0.
 */
static inline void cpu_set_reserved_ttbr0(void)
{
	unsigned long ttbr = virt_to_phys(empty_zero_page);

	write_sysreg(ttbr, ttbr0_el1);
	isb();
}

/*
 * TCR.T0SZ value to use when the ID map is active. Usually equals
 * TCR_T0SZ(VA_BITS), unless system RAM is positioned very high in
 * physical memory, in which case it will be smaller.
 */
extern u64 idmap_t0sz;

static inline bool __cpu_uses_extended_idmap(void)
{
	return (!IS_ENABLED(CONFIG_ARM64_VA_BITS_48) &&
		unlikely(idmap_t0sz != TCR_T0SZ(VA_BITS)));
}

/*
 * Set TCR.T0SZ to its default value (based on VA_BITS)
 */
static inline void __cpu_set_tcr_t0sz(unsigned long t0sz)
{
	unsigned long tcr;

	if (!__cpu_uses_extended_idmap())
		return;

	tcr = read_sysreg(tcr_el1);
	tcr &= ~TCR_T0SZ_MASK;
	tcr |= t0sz << TCR_T0SZ_OFFSET;
	write_sysreg(tcr, tcr_el1);
	isb();
}

#define cpu_set_default_tcr_t0sz()	__cpu_set_tcr_t0sz(TCR_T0SZ(VA_BITS))
#define cpu_set_idmap_tcr_t0sz()	__cpu_set_tcr_t0sz(idmap_t0sz)

/*
 * Remove the idmap from TTBR0_EL1 and install the pgd of the active mm.
 *
 * The idmap lives in the same VA range as userspace, but uses global entries
 * and may use a different TCR_EL1.T0SZ. To avoid issues resulting from
 * speculative TLB fetches, we must temporarily install the reserved page
 * tables while we invalidate the TLBs and set up the correct TCR_EL1.T0SZ.
 *
 * If current is a not a user task, the mm covers the TTBR1_EL1 page tables,
 * which should not be installed in TTBR0_EL1. In this case we can leave the
 * reserved page tables in place.
 */
static inline void cpu_uninstall_idmap(void)
{
	struct mm_struct *mm = current->active_mm;

	cpu_set_reserved_ttbr0();
	local_flush_tlb_all();
	cpu_set_default_tcr_t0sz();

	if (mm != &init_mm && !system_uses_ttbr0_pan())
		cpu_switch_mm(mm->pgd, mm);
}

static inline void cpu_install_idmap(void)
{
	cpu_set_reserved_ttbr0();
	local_flush_tlb_all();
	cpu_set_idmap_tcr_t0sz();

	cpu_switch_mm(idmap_pg_dir, &init_mm);
}

/*
 * Atomically replaces the active TTBR1_EL1 PGD with a new VA-compatible PGD,
 * avoiding the possibility of conflicting TLB entries being allocated.
 */
static inline void cpu_replace_ttbr1(pgd_t *pgd)
{
	typedef void (ttbr_replace_func)(phys_addr_t);
	extern ttbr_replace_func idmap_cpu_replace_ttbr1;
	ttbr_replace_func *replace_phys;

	phys_addr_t pgd_phys = virt_to_phys(pgd);

	replace_phys = (void *)virt_to_phys(idmap_cpu_replace_ttbr1);

	cpu_install_idmap();
	replace_phys(pgd_phys);
	cpu_uninstall_idmap();
}

/*
 * It would be nice to return ASIDs back to the allocator, but unfortunately
 * that introduces a race with a generation rollover where we could erroneously
 * free an ASID allocated in a future generation. We could workaround this by
 * freeing the ASID from the context of the dying mm (e.g. in arch_exit_mmap),
 * but we'd then need to make sure that we didn't dirty any TLBs afterwards.
 * Setting a reserved TTBR0 or EPD0 would work, but it all gets ugly when you
 * take CPU migration into account.
 */
#define destroy_context(mm)		do { } while(0)
void check_and_switch_context(struct mm_struct *mm, unsigned int cpu);

#define init_new_context(tsk,mm)	({ atomic64_set(&(mm)->context.id, 0); 0; })

/*
 * This is called when "tsk" is about to enter lazy TLB mode.
 *
 * mm:  describes the currently active mm context
 * tsk: task which is entering lazy tlb
 * cpu: cpu number which is entering lazy tlb
 *
 * tsk->mm will be NULL
 */
static inline void
enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
{
}

#ifdef CONFIG_ARM64_SW_TTBR0_PAN
static inline void update_saved_ttbr0(struct task_struct *tsk,
				      struct mm_struct *mm)
{
	if (system_uses_ttbr0_pan()) {
		BUG_ON(mm->pgd == swapper_pg_dir);
		task_thread_info(tsk)->ttbr0 =
			virt_to_phys(mm->pgd) | ASID(mm) << 48;
	}
}
#else
static inline void update_saved_ttbr0(struct task_struct *tsk,
				      struct mm_struct *mm)
{
}
#endif

static inline void __switch_mm(struct mm_struct *next)
{
	unsigned int cpu = smp_processor_id();

	/*
	 * init_mm.pgd does not contain any user mappings and it is always
	 * active for kernel addresses in TTBR1. Just set the reserved TTBR0.
	 */
	if (next == &init_mm) {
		cpu_set_reserved_ttbr0();
		return;
	}

	check_and_switch_context(next, cpu);
}

static inline void
switch_mm(struct mm_struct *prev, struct mm_struct *next,
	  struct task_struct *tsk)
{
	if (prev != next)
		__switch_mm(next);

	/*
	 * Update the saved TTBR0_EL1 of the scheduled-in task as the previous
	 * value may have not been initialised yet (activate_mm caller) or the
	 * ASID has changed since the last run (following the context switch
	 * of another thread of the same process). Avoid setting the reserved
	 * TTBR0_EL1 to swapper_pg_dir (init_mm; e.g. via idle_task_exit).
	 */
	if (next != &init_mm)
		update_saved_ttbr0(tsk, next);
}

#define deactivate_mm(tsk,mm)	do { } while (0)
#define activate_mm(prev,next)	switch_mm(prev, next, current)

void verify_cpu_asid_bits(void);

#endif