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

INCLUDED FROM

DEFINITIONS

1. contextidr_thread_switch
2. cpu_set_reserved_ttbr0
3. cpu_switch_mm
4. __cpu_uses_extended_idmap
5. __cpu_uses_extended_idmap_level
6. __cpu_set_tcr_t0sz
7. cpu_uninstall_idmap
8. cpu_install_idmap
9. cpu_replace_ttbr1
10. update_saved_ttbr0
11. update_saved_ttbr0
12. enter_lazy_tlb
13. __switch_mm
14. switch_mm

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * Based on arch/arm/include/asm/mmu_context.h
   4  *
   5  * Copyright (C) 1996 Russell King.
   6  * Copyright (C) 2012 ARM Ltd.
   7  */
   8 #ifndef __ASM_MMU_CONTEXT_H
   9 #define __ASM_MMU_CONTEXT_H
  10 
  11 #ifndef __ASSEMBLY__
  12 
  13 #include <linux/compiler.h>
  14 #include <linux/sched.h>
  15 #include <linux/sched/hotplug.h>
  16 #include <linux/mm_types.h>
  17 
  18 #include <asm/cacheflush.h>
  19 #include <asm/cpufeature.h>
  20 #include <asm/proc-fns.h>
  21 #include <asm-generic/mm_hooks.h>
  22 #include <asm/cputype.h>
  23 #include <asm/pgtable.h>
  24 #include <asm/sysreg.h>
  25 #include <asm/tlbflush.h>
  26 
  27 extern bool rodata_full;
  28 
  29 static inline void contextidr_thread_switch(struct task_struct *next)
  30 {
  31         if (!IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR))
  32                 return;
  33 
  34         write_sysreg(task_pid_nr(next), contextidr_el1);
  35         isb();
  36 }
  37 
  38 /*
  39  * Set TTBR0 to empty_zero_page. No translations will be possible via TTBR0.
  40  */
  41 static inline void cpu_set_reserved_ttbr0(void)
  42 {
  43         unsigned long ttbr = phys_to_ttbr(__pa_symbol(empty_zero_page));
  44 
  45         write_sysreg(ttbr, ttbr0_el1);
  46         isb();
  47 }
  48 
  49 static inline void cpu_switch_mm(pgd_t *pgd, struct mm_struct *mm)
  50 {
  51         BUG_ON(pgd == swapper_pg_dir);
  52         cpu_set_reserved_ttbr0();
  53         cpu_do_switch_mm(virt_to_phys(pgd),mm);
  54 }
  55 
  56 /*
  57  * TCR.T0SZ value to use when the ID map is active. Usually equals
  58  * TCR_T0SZ(VA_BITS), unless system RAM is positioned very high in
  59  * physical memory, in which case it will be smaller.
  60  */
  61 extern u64 idmap_t0sz;
  62 extern u64 idmap_ptrs_per_pgd;
  63 
  64 static inline bool __cpu_uses_extended_idmap(void)
  65 {
  66         if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52))
  67                 return false;
  68 
  69         return unlikely(idmap_t0sz != TCR_T0SZ(VA_BITS));
  70 }
  71 
  72 /*
  73  * True if the extended ID map requires an extra level of translation table
  74  * to be configured.
  75  */
  76 static inline bool __cpu_uses_extended_idmap_level(void)
  77 {
  78         return ARM64_HW_PGTABLE_LEVELS(64 - idmap_t0sz) > CONFIG_PGTABLE_LEVELS;
  79 }
  80 
  81 /*
  82  * Set TCR.T0SZ to its default value (based on VA_BITS)
  83  */
  84 static inline void __cpu_set_tcr_t0sz(unsigned long t0sz)
  85 {
  86         unsigned long tcr;
  87 
  88         if (!__cpu_uses_extended_idmap())
  89                 return;
  90 
  91         tcr = read_sysreg(tcr_el1);
  92         tcr &= ~TCR_T0SZ_MASK;
  93         tcr |= t0sz << TCR_T0SZ_OFFSET;
  94         write_sysreg(tcr, tcr_el1);
  95         isb();
  96 }
  97 
  98 #define cpu_set_default_tcr_t0sz()      __cpu_set_tcr_t0sz(TCR_T0SZ(vabits_actual))
  99 #define cpu_set_idmap_tcr_t0sz()        __cpu_set_tcr_t0sz(idmap_t0sz)
 100 
 101 /*
 102  * Remove the idmap from TTBR0_EL1 and install the pgd of the active mm.
 103  *
 104  * The idmap lives in the same VA range as userspace, but uses global entries
 105  * and may use a different TCR_EL1.T0SZ. To avoid issues resulting from
 106  * speculative TLB fetches, we must temporarily install the reserved page
 107  * tables while we invalidate the TLBs and set up the correct TCR_EL1.T0SZ.
 108  *
 109  * If current is a not a user task, the mm covers the TTBR1_EL1 page tables,
 110  * which should not be installed in TTBR0_EL1. In this case we can leave the
 111  * reserved page tables in place.
 112  */
 113 static inline void cpu_uninstall_idmap(void)
 114 {
 115         struct mm_struct *mm = current->active_mm;
 116 
 117         cpu_set_reserved_ttbr0();
 118         local_flush_tlb_all();
 119         cpu_set_default_tcr_t0sz();
 120 
 121         if (mm != &init_mm && !system_uses_ttbr0_pan())
 122                 cpu_switch_mm(mm->pgd, mm);
 123 }
 124 
 125 static inline void cpu_install_idmap(void)
 126 {
 127         cpu_set_reserved_ttbr0();
 128         local_flush_tlb_all();
 129         cpu_set_idmap_tcr_t0sz();
 130 
 131         cpu_switch_mm(lm_alias(idmap_pg_dir), &init_mm);
 132 }
 133 
 134 /*
 135  * Atomically replaces the active TTBR1_EL1 PGD with a new VA-compatible PGD,
 136  * avoiding the possibility of conflicting TLB entries being allocated.
 137  */
 138 static inline void cpu_replace_ttbr1(pgd_t *pgdp)
 139 {
 140         typedef void (ttbr_replace_func)(phys_addr_t);
 141         extern ttbr_replace_func idmap_cpu_replace_ttbr1;
 142         ttbr_replace_func *replace_phys;
 143 
 144         /* phys_to_ttbr() zeros lower 2 bits of ttbr with 52-bit PA */
 145         phys_addr_t ttbr1 = phys_to_ttbr(virt_to_phys(pgdp));
 146 
 147         if (system_supports_cnp() && !WARN_ON(pgdp != lm_alias(swapper_pg_dir))) {
 148                 /*
 149                  * cpu_replace_ttbr1() is used when there's a boot CPU
 150                  * up (i.e. cpufeature framework is not up yet) and
 151                  * latter only when we enable CNP via cpufeature's
 152                  * enable() callback.
 153                  * Also we rely on the cpu_hwcap bit being set before
 154                  * calling the enable() function.
 155                  */
 156                 ttbr1 |= TTBR_CNP_BIT;
 157         }
 158 
 159         replace_phys = (void *)__pa_symbol(idmap_cpu_replace_ttbr1);
 160 
 161         cpu_install_idmap();
 162         replace_phys(ttbr1);
 163         cpu_uninstall_idmap();
 164 }
 165 
 166 /*
 167  * It would be nice to return ASIDs back to the allocator, but unfortunately
 168  * that introduces a race with a generation rollover where we could erroneously
 169  * free an ASID allocated in a future generation. We could workaround this by
 170  * freeing the ASID from the context of the dying mm (e.g. in arch_exit_mmap),
 171  * but we'd then need to make sure that we didn't dirty any TLBs afterwards.
 172  * Setting a reserved TTBR0 or EPD0 would work, but it all gets ugly when you
 173  * take CPU migration into account.
 174  */
 175 #define destroy_context(mm)             do { } while(0)
 176 void check_and_switch_context(struct mm_struct *mm, unsigned int cpu);
 177 
 178 #define init_new_context(tsk,mm)        ({ atomic64_set(&(mm)->context.id, 0); 0; })
 179 
 180 #ifdef CONFIG_ARM64_SW_TTBR0_PAN
 181 static inline void update_saved_ttbr0(struct task_struct *tsk,
 182                                       struct mm_struct *mm)
 183 {
 184         u64 ttbr;
 185 
 186         if (!system_uses_ttbr0_pan())
 187                 return;
 188 
 189         if (mm == &init_mm)
 190                 ttbr = __pa_symbol(empty_zero_page);
 191         else
 192                 ttbr = virt_to_phys(mm->pgd) | ASID(mm) << 48;
 193 
 194         WRITE_ONCE(task_thread_info(tsk)->ttbr0, ttbr);
 195 }
 196 #else
 197 static inline void update_saved_ttbr0(struct task_struct *tsk,
 198                                       struct mm_struct *mm)
 199 {
 200 }
 201 #endif
 202 
 203 static inline void
 204 enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
 205 {
 206         /*
 207          * We don't actually care about the ttbr0 mapping, so point it at the
 208          * zero page.
 209          */
 210         update_saved_ttbr0(tsk, &init_mm);
 211 }
 212 
 213 static inline void __switch_mm(struct mm_struct *next)
 214 {
 215         unsigned int cpu = smp_processor_id();
 216 
 217         /*
 218          * init_mm.pgd does not contain any user mappings and it is always
 219          * active for kernel addresses in TTBR1. Just set the reserved TTBR0.
 220          */
 221         if (next == &init_mm) {
 222                 cpu_set_reserved_ttbr0();
 223                 return;
 224         }
 225 
 226         check_and_switch_context(next, cpu);
 227 }
 228 
 229 static inline void
 230 switch_mm(struct mm_struct *prev, struct mm_struct *next,
 231           struct task_struct *tsk)
 232 {
 233         if (prev != next)
 234                 __switch_mm(next);
 235 
 236         /*
 237          * Update the saved TTBR0_EL1 of the scheduled-in task as the previous
 238          * value may have not been initialised yet (activate_mm caller) or the
 239          * ASID has changed since the last run (following the context switch
 240          * of another thread of the same process).
 241          */
 242         update_saved_ttbr0(tsk, next);
 243 }
 244 
 245 #define deactivate_mm(tsk,mm)   do { } while (0)
 246 #define activate_mm(prev,next)  switch_mm(prev, next, current)
 247 
 248 void verify_cpu_asid_bits(void);
 249 void post_ttbr_update_workaround(void);
 250 
 251 #endif /* !__ASSEMBLY__ */
 252 
 253 #endif /* !__ASM_MMU_CONTEXT_H */