arch/x86/mm/cpu_entry_area.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include <linux/spinlock.h>
   4 #include <linux/percpu.h>
   5
   6 #include <asm/cpu_entry_area.h>
   7 #include <asm/pgtable.h>
   8 #include <asm/fixmap.h>
   9 #include <asm/desc.h>
  10
  11 static DEFINE_PER_CPU_PAGE_ALIGNED(struct entry_stack_page, entry_stack_storage);
  12
  13 #ifdef CONFIG_X86_64
  14 static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
  15         [(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]);
  16 #endif
  17
  18 struct cpu_entry_area *get_cpu_entry_area(int cpu)
  19 {
  20         unsigned long va = CPU_ENTRY_AREA_PER_CPU + cpu * CPU_ENTRY_AREA_SIZE;
  21         BUILD_BUG_ON(sizeof(struct cpu_entry_area) % PAGE_SIZE != 0);
  22
  23         return (struct cpu_entry_area *) va;
  24 }
  25 EXPORT_SYMBOL(get_cpu_entry_area);
  26
  27 void cea_set_pte(void *cea_vaddr, phys_addr_t pa, pgprot_t flags)
  28 {
  29         unsigned long va = (unsigned long) cea_vaddr;
  30
  31         set_pte_vaddr(va, pfn_pte(pa >> PAGE_SHIFT, flags));
  32 }
  33
  34 static void __init
  35 cea_map_percpu_pages(void *cea_vaddr, void *ptr, int pages, pgprot_t prot)
  36 {
  37         for ( ; pages; pages--, cea_vaddr+= PAGE_SIZE, ptr += PAGE_SIZE)
  38                 cea_set_pte(cea_vaddr, per_cpu_ptr_to_phys(ptr), prot);
  39 }
  40
  41 static void percpu_setup_debug_store(int cpu)
  42 {
  43 #ifdef CONFIG_CPU_SUP_INTEL
  44         int npages;
  45         void *cea;
  46
  47         if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
  48                 return;
  49
  50         cea = &get_cpu_entry_area(cpu)->cpu_debug_store;
  51         npages = sizeof(struct debug_store) / PAGE_SIZE;
  52         BUILD_BUG_ON(sizeof(struct debug_store) % PAGE_SIZE != 0);
  53         cea_map_percpu_pages(cea, &per_cpu(cpu_debug_store, cpu), npages,
  54                              PAGE_KERNEL);
  55
  56         cea = &get_cpu_entry_area(cpu)->cpu_debug_buffers;
  57         /*
  58          * Force the population of PMDs for not yet allocated per cpu
  59          * memory like debug store buffers.
  60          */
  61         npages = sizeof(struct debug_store_buffers) / PAGE_SIZE;
  62         for (; npages; npages--, cea += PAGE_SIZE)
  63                 cea_set_pte(cea, 0, PAGE_NONE);
  64 #endif
  65 }
  66
  67 /* Setup the fixmap mappings only once per-processor */
  68 static void __init setup_cpu_entry_area(int cpu)
  69 {
  70 #ifdef CONFIG_X86_64
  71         extern char _entry_trampoline[];
  72
  73         /* On 64-bit systems, we use a read-only fixmap GDT and TSS. */
  74         pgprot_t gdt_prot = PAGE_KERNEL_RO;
  75         pgprot_t tss_prot = PAGE_KERNEL_RO;
  76 #else
  77         /*
  78          * On native 32-bit systems, the GDT cannot be read-only because
  79          * our double fault handler uses a task gate, and entering through
  80          * a task gate needs to change an available TSS to busy.  If the
  81          * GDT is read-only, that will triple fault.  The TSS cannot be
  82          * read-only because the CPU writes to it on task switches.
  83          *
  84          * On Xen PV, the GDT must be read-only because the hypervisor
  85          * requires it.
  86          */
  87         pgprot_t gdt_prot = boot_cpu_has(X86_FEATURE_XENPV) ?
  88                 PAGE_KERNEL_RO : PAGE_KERNEL;
  89         pgprot_t tss_prot = PAGE_KERNEL;
  90 #endif
  91
  92         cea_set_pte(&get_cpu_entry_area(cpu)->gdt, get_cpu_gdt_paddr(cpu),
  93                     gdt_prot);
  94
  95         cea_map_percpu_pages(&get_cpu_entry_area(cpu)->entry_stack_page,
  96                              per_cpu_ptr(&entry_stack_storage, cpu), 1,
  97                              PAGE_KERNEL);
  98
  99         /*
 100          * The Intel SDM says (Volume 3, 7.2.1):
 101          *
 102          *  Avoid placing a page boundary in the part of the TSS that the
 103          *  processor reads during a task switch (the first 104 bytes). The
 104          *  processor may not correctly perform address translations if a
 105          *  boundary occurs in this area. During a task switch, the processor
 106          *  reads and writes into the first 104 bytes of each TSS (using
 107          *  contiguous physical addresses beginning with the physical address
 108          *  of the first byte of the TSS). So, after TSS access begins, if
 109          *  part of the 104 bytes is not physically contiguous, the processor
 110          *  will access incorrect information without generating a page-fault
 111          *  exception.
 112          *
 113          * There are also a lot of errata involving the TSS spanning a page
 114          * boundary.  Assert that we're not doing that.
 115          */
 116         BUILD_BUG_ON((offsetof(struct tss_struct, x86_tss) ^
 117                       offsetofend(struct tss_struct, x86_tss)) & PAGE_MASK);
 118         BUILD_BUG_ON(sizeof(struct tss_struct) % PAGE_SIZE != 0);
 119         cea_map_percpu_pages(&get_cpu_entry_area(cpu)->tss,
 120                              &per_cpu(cpu_tss_rw, cpu),
 121                              sizeof(struct tss_struct) / PAGE_SIZE, tss_prot);
 122
 123 #ifdef CONFIG_X86_32
 124         per_cpu(cpu_entry_area, cpu) = get_cpu_entry_area(cpu);
 125 #endif
 126
 127 #ifdef CONFIG_X86_64
 128         BUILD_BUG_ON(sizeof(exception_stacks) % PAGE_SIZE != 0);
 129         BUILD_BUG_ON(sizeof(exception_stacks) !=
 130                      sizeof(((struct cpu_entry_area *)0)->exception_stacks));
 131         cea_map_percpu_pages(&get_cpu_entry_area(cpu)->exception_stacks,
 132                              &per_cpu(exception_stacks, cpu),
 133                              sizeof(exception_stacks) / PAGE_SIZE, PAGE_KERNEL);
 134
 135         cea_set_pte(&get_cpu_entry_area(cpu)->entry_trampoline,
 136                      __pa_symbol(_entry_trampoline), PAGE_KERNEL_RX);
 137 #endif
 138         percpu_setup_debug_store(cpu);
 139 }
 140
 141 static __init void setup_cpu_entry_area_ptes(void)
 142 {
 143 #ifdef CONFIG_X86_32
 144         unsigned long start, end;
 145
 146         BUILD_BUG_ON(CPU_ENTRY_AREA_PAGES * PAGE_SIZE < CPU_ENTRY_AREA_MAP_SIZE);
 147         BUG_ON(CPU_ENTRY_AREA_BASE & ~PMD_MASK);
 148
 149         start = CPU_ENTRY_AREA_BASE;
 150         end = start + CPU_ENTRY_AREA_MAP_SIZE;
 151
 152         /* Careful here: start + PMD_SIZE might wrap around */
 153         for (; start < end && start >= CPU_ENTRY_AREA_BASE; start += PMD_SIZE)
 154                 populate_extra_pte(start);
 155 #endif
 156 }
 157
 158 void __init setup_cpu_entry_areas(void)
 159 {
 160         unsigned int cpu;
 161
 162         setup_cpu_entry_area_ptes();
 163
 164         for_each_possible_cpu(cpu)
 165                 setup_cpu_entry_area(cpu);
 166 }