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x86, 64bit: Use a #PF handler to materialize early mappings on demand

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Linear mode (CR0.PG = 0) is mutually exclusive with 64-bit mode; all
64-bit code has to use page tables.  This makes it awkward before we
have first set up properly all-covering page tables to access objects
that are outside the static kernel range.

So far we have dealt with that simply by mapping a fixed amount of
low memory, but that fails in at least two upcoming use cases:

1. We will support load and run kernel, struct boot_params, ramdisk,
   command line, etc. above the 4 GiB mark.
2. need to access ramdisk early to get microcode to update that as
   early possible.

We could use early_iomap to access them too, but it will make code to
messy and hard to be unified with 32 bit.

Hence, set up a #PF table and use a fixed number of buffers to set up
page tables on demand.  If the buffers fill up then we simply flush
them and start over.  These buffers are all in __initdata, so it does
not increase RAM usage at runtime.

Thus, with the help of the #PF handler, we can set the final kernel
mapping from blank, and switch to init_level4_pgt later.

During the switchover in head_64.S, before #PF handler is available,
we use three pages to handle kernel crossing 1G, 512G boundaries with
sharing page by playing games with page aliasing: the same page is
mapped twice in the higher-level tables with appropriate wraparound.
The kernel region itself will be properly mapped; other mappings may
be spurious.

early_make_pgtable is using kernel high mapping address to access pages
to set page table.

-v4: Add phys_base offset to make kexec happy, and add
	init_mapping_kernel()   - Yinghai
-v5: fix compiling with xen, and add back ident level3 and level2 for xen
     also move back init_level4_pgt from BSS to DATA again.
     because we have to clear it anyway.  - Yinghai
-v6: switch to init_level4_pgt in init_mem_mapping. - Yinghai
-v7: remove not needed clear_page for init_level4_page
     it is with fill 512,8,0 already in head_64.S  - Yinghai
-v8: we need to keep that handler alive until init_mem_mapping and don't
     let early_trap_init to trash that early #PF handler.
     So split early_trap_pf_init out and move it down. - Yinghai
-v9: switchover only cover kernel space instead of 1G so could avoid
     touch possible mem holes. - Yinghai
-v11: change far jmp back to far return to initial_code, that is needed
     to fix failure that is reported by Konrad on AMD systems.  - Yinghai

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1359058816-7615-12-git-send-email-yinghai@kernel.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
H. Peter Anvin 2013-01-24 12:19:52 -08:00 • committed by H. Peter Anvin
parent 4f7b92263a
commit 8170e6bed4
7 changed files with 221 additions and 93 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
arch/x86/include/asm/pgtable_64_types.h
View file

@ -1,6 +1,8 @@
#ifndef _ASM_X86_PGTABLE_64_DEFS_H
#define _ASM_X86_PGTABLE_64_DEFS_H
#include <asm/sparsemem.h>
#ifndef __ASSEMBLY__
#include <linux/types.h>
@ -60,4 +62,6 @@ typedef struct { pteval_t pte; } pte_t;
#define MODULES_END _AC(0xffffffffff000000, UL)
#define MODULES_LEN (MODULES_END - MODULES_VADDR)
#define EARLY_DYNAMIC_PAGE_TABLES 64
#endif /* _ASM_X86_PGTABLE_64_DEFS_H */

1
arch/x86/include/asm/processor.h
View file

@ -731,6 +731,7 @@ extern void enable_sep_cpu(void);
extern int sysenter_setup(void);
extern void early_trap_init(void);
void early_trap_pf_init(void);
/* Defined in head.S */
extern struct desc_ptr early_gdt_descr;

81
arch/x86/kernel/head64.c
View file

@ -27,11 +27,73 @@
#include <asm/bios_ebda.h>
#include <asm/bootparam_utils.h>
static void __init zap_identity_mappings(void)
/*
* Manage page tables very early on.
*/
extern pgd_t early_level4_pgt[PTRS_PER_PGD];
extern pmd_t early_dynamic_pgts[EARLY_DYNAMIC_PAGE_TABLES][PTRS_PER_PMD];
static unsigned int __initdata next_early_pgt = 2;
/* Wipe all early page tables except for the kernel symbol map */
static void __init reset_early_page_tables(void)
{
pgd_t *pgd = pgd_offset_k(0UL);
pgd_clear(pgd);
__flush_tlb_all();
unsigned long i;
for (i = 0; i < PTRS_PER_PGD-1; i++)
early_level4_pgt[i].pgd = 0;
next_early_pgt = 0;
write_cr3(__pa(early_level4_pgt));
}
/* Create a new PMD entry */
int __init early_make_pgtable(unsigned long address)
{
unsigned long physaddr = address - __PAGE_OFFSET;
unsigned long i;
pgdval_t pgd, *pgd_p;
pudval_t *pud_p;
pmdval_t pmd, *pmd_p;
/* Invalid address or early pgt is done ? */
if (physaddr >= MAXMEM || read_cr3() != __pa(early_level4_pgt))
return -1;
i = (address >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1);
pgd_p = &early_level4_pgt[i].pgd;
pgd = *pgd_p;
/*
* The use of __START_KERNEL_map rather than __PAGE_OFFSET here is
* critical -- __PAGE_OFFSET would point us back into the dynamic
* range and we might end up looping forever...
*/
if (pgd && next_early_pgt < EARLY_DYNAMIC_PAGE_TABLES) {
pud_p = (pudval_t *)((pgd & PTE_PFN_MASK) + __START_KERNEL_map - phys_base);
} else {
if (next_early_pgt >= EARLY_DYNAMIC_PAGE_TABLES-1)
reset_early_page_tables();
pud_p = (pudval_t *)early_dynamic_pgts[next_early_pgt++];
for (i = 0; i < PTRS_PER_PUD; i++)
pud_p[i] = 0;
*pgd_p = (pgdval_t)pud_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
}
i = (address >> PUD_SHIFT) & (PTRS_PER_PUD - 1);
pud_p += i;
pmd_p = (pmdval_t *)early_dynamic_pgts[next_early_pgt++];
pmd = (physaddr & PUD_MASK) + (__PAGE_KERNEL_LARGE & ~_PAGE_GLOBAL);
for (i = 0; i < PTRS_PER_PMD; i++) {
pmd_p[i] = pmd;
pmd += PMD_SIZE;
}
*pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
return 0;
}
/* Don't add a printk in there. printk relies on the PDA which is not initialized
@ -72,12 +134,13 @@ void __init x86_64_start_kernel(char * real_mode_data)
(__START_KERNEL & PGDIR_MASK)));
BUILD_BUG_ON(__fix_to_virt(__end_of_fixed_addresses) <= MODULES_END);
/* Kill off the identity-map trampoline */
reset_early_page_tables();
/* clear bss before set_intr_gate with early_idt_handler */
clear_bss();
/* Make NULL pointers segfault */
zap_identity_mappings();
/* XXX - this is wrong... we need to build page tables from scratch */
max_pfn_mapped = KERNEL_IMAGE_SIZE >> PAGE_SHIFT;
for (i = 0; i < NUM_EXCEPTION_VECTORS; i++) {
@ -94,6 +157,10 @@ void __init x86_64_start_kernel(char * real_mode_data)
if (console_loglevel == 10)
early_printk("Kernel alive\n");
clear_page(init_level4_pgt);
/* set init_level4_pgt kernel high mapping*/
init_level4_pgt[511] = early_level4_pgt[511];
x86_64_start_reservations(real_mode_data);
}

214
arch/x86/kernel/head_64.S
View file

@ -47,14 +47,13 @@ L3_START_KERNEL = pud_index(__START_KERNEL_map)
.code64
.globl startup_64
startup_64:
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 1,
* and someone has loaded an identity mapped page table
* for us. These identity mapped page tables map all of the
* kernel pages and possibly all of memory.
*
* %esi holds a physical pointer to real_mode_data.
* %rsi holds a physical pointer to real_mode_data.
*
* We come here either directly from a 64bit bootloader, or from
* arch/x86_64/boot/compressed/head.S.
@ -66,7 +65,8 @@ startup_64:
* tables and then reload them.
*/
/* Compute the delta between the address I am compiled to run at and the
/*
* Compute the delta between the address I am compiled to run at and the
* address I am actually running at.
*/
leaq _text(%rip), %rbp
@ -78,45 +78,62 @@ startup_64:
testl %eax, %eax
jnz bad_address
/* Is the address too large? */
leaq _text(%rip), %rdx
movq $PGDIR_SIZE, %rax
cmpq %rax, %rdx
jae bad_address
/* Fixup the physical addresses in the page table
/*
* Is the address too large?
*/
addq %rbp, init_level4_pgt + 0(%rip)
addq %rbp, init_level4_pgt + (L4_PAGE_OFFSET*8)(%rip)
addq %rbp, init_level4_pgt + (L4_START_KERNEL*8)(%rip)
leaq _text(%rip), %rax
shrq $MAX_PHYSMEM_BITS, %rax
jnz bad_address
addq %rbp, level3_ident_pgt + 0(%rip)
/*
* Fixup the physical addresses in the page table
*/
addq %rbp, early_level4_pgt + (L4_START_KERNEL*8)(%rip)
addq %rbp, level3_kernel_pgt + (510*8)(%rip)
addq %rbp, level3_kernel_pgt + (511*8)(%rip)
addq %rbp, level2_fixmap_pgt + (506*8)(%rip)
/* Add an Identity mapping if I am above 1G */
/*
* Set up the identity mapping for the switchover. These
* entries should *NOT* have the global bit set! This also
* creates a bunch of nonsense entries but that is fine --
* it avoids problems around wraparound.
*/
leaq _text(%rip), %rdi
andq $PMD_PAGE_MASK, %rdi
leaq early_level4_pgt(%rip), %rbx
movq %rdi, %rax
shrq $PGDIR_SHIFT, %rax
leaq (4096 + _KERNPG_TABLE)(%rbx), %rdx
movq %rdx, 0(%rbx,%rax,8)
movq %rdx, 8(%rbx,%rax,8)
addq $4096, %rdx
movq %rdi, %rax
shrq $PUD_SHIFT, %rax
andq $(PTRS_PER_PUD - 1), %rax
jz ident_complete
leaq (level2_spare_pgt - __START_KERNEL_map + _KERNPG_TABLE)(%rbp), %rdx
leaq level3_ident_pgt(%rip), %rbx
movq %rdx, 0(%rbx, %rax, 8)
andl $(PTRS_PER_PUD-1), %eax
movq %rdx, (4096+0)(%rbx,%rax,8)
movq %rdx, (4096+8)(%rbx,%rax,8)
addq $8192, %rbx
movq %rdi, %rax
shrq $PMD_SHIFT, %rax
andq $(PTRS_PER_PMD - 1), %rax
leaq __PAGE_KERNEL_IDENT_LARGE_EXEC(%rdi), %rdx
leaq level2_spare_pgt(%rip), %rbx
movq %rdx, 0(%rbx, %rax, 8)
ident_complete:
shrq $PMD_SHIFT, %rdi
addq $(__PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL), %rax
leaq (_end - 1)(%rip), %rcx
shrq $PMD_SHIFT, %rcx
subq %rdi, %rcx
incl %ecx
1:
andq $(PTRS_PER_PMD - 1), %rdi
movq %rax, (%rbx,%rdi,8)
incq %rdi
addq $PMD_SIZE, %rax
decl %ecx
jnz 1b
/*
* Fixup the kernel text+data virtual addresses. Note that
@ -124,7 +141,6 @@ ident_complete:
* cleanup_highmap() fixes this up along with the mappings
* beyond _end.
*/
leaq level2_kernel_pgt(%rip), %rdi
leaq 4096(%rdi), %r8
/* See if it is a valid page table entry */
@ -139,17 +155,14 @@ ident_complete:
/* Fixup phys_base */
addq %rbp, phys_base(%rip)
/* Due to ENTRY(), sometimes the empty space gets filled with
* zeros. Better take a jmp than relying on empty space being
* filled with 0x90 (nop)
*/
jmp secondary_startup_64
movq $(early_level4_pgt - __START_KERNEL_map), %rax
jmp 1f
ENTRY(secondary_startup_64)
/*
* At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 1,
* and someone has loaded a mapped page table.
*
* %esi holds a physical pointer to real_mode_data.
* %rsi holds a physical pointer to real_mode_data.
*
* We come here either from startup_64 (using physical addresses)
* or from trampoline.S (using virtual addresses).
@ -159,12 +172,14 @@ ENTRY(secondary_startup_64)
* after the boot processor executes this code.
*/
movq $(init_level4_pgt - __START_KERNEL_map), %rax
1:
/* Enable PAE mode and PGE */
movl $(X86_CR4_PAE | X86_CR4_PGE), %eax
movq %rax, %cr4
movl $(X86_CR4_PAE | X86_CR4_PGE), %ecx
movq %rcx, %cr4
/* Setup early boot stage 4 level pagetables. */
movq $(init_level4_pgt - __START_KERNEL_map), %rax
addq phys_base(%rip), %rax
movq %rax, %cr3
@ -196,7 +211,7 @@ ENTRY(secondary_startup_64)
movq %rax, %cr0
/* Setup a boot time stack */
movq stack_start(%rip),%rsp
movq stack_start(%rip), %rsp
/* zero EFLAGS after setting rsp */
pushq $0
@ -236,15 +251,33 @@ ENTRY(secondary_startup_64)
movl initial_gs+4(%rip),%edx
wrmsr
/* esi is pointer to real mode structure with interesting info.
/* rsi is pointer to real mode structure with interesting info.
pass it to C */
movl %esi, %edi
movq %rsi, %rdi
/* Finally jump to run C code and to be on real kernel address
* Since we are running on identity-mapped space we have to jump
* to the full 64bit address, this is only possible as indirect
* jump. In addition we need to ensure %cs is set so we make this
* a far return.
*
* Note: do not change to far jump indirect with 64bit offset.
*
* AMD does not support far jump indirect with 64bit offset.
* AMD64 Architecture Programmer's Manual, Volume 3: states only
* JMP FAR mem16:16 FF /5 Far jump indirect,
* with the target specified by a far pointer in memory.
* JMP FAR mem16:32 FF /5 Far jump indirect,
* with the target specified by a far pointer in memory.
*
* Intel64 does support 64bit offset.
* Software Developer Manual Vol 2: states:
* FF /5 JMP m16:16 Jump far, absolute indirect,
* address given in m16:16
* FF /5 JMP m16:32 Jump far, absolute indirect,
* address given in m16:32.
* REX.W + FF /5 JMP m16:64 Jump far, absolute indirect,
* address given in m16:64.
*/
movq initial_code(%rip),%rax
pushq $0 # fake return address to stop unwinder
@ -270,13 +303,13 @@ ENDPROC(start_cpu0)
/* SMP bootup changes these two */
__REFDATA
.align 8
ENTRY(initial_code)
.balign 8
GLOBAL(initial_code)
.quad x86_64_start_kernel
ENTRY(initial_gs)
GLOBAL(initial_gs)
.quad INIT_PER_CPU_VAR(irq_stack_union)
ENTRY(stack_start)
GLOBAL(stack_start)
.quad init_thread_union+THREAD_SIZE-8
.word 0
__FINITDATA
@ -284,7 +317,7 @@ ENDPROC(start_cpu0)
bad_address:
jmp bad_address
.section ".init.text","ax"
__INIT
.globl early_idt_handlers
early_idt_handlers:
# 104(%rsp) %rflags
@ -321,14 +354,22 @@ ENTRY(early_idt_handler)
pushq %r11 # 0(%rsp)
cmpl $__KERNEL_CS,96(%rsp)
jne 10f
jne 11f
cmpl $14,72(%rsp) # Page fault?
jnz 10f
GET_CR2_INTO(%rdi) # can clobber any volatile register if pv
call early_make_pgtable
andl %eax,%eax
jz 20f # All good
10:
leaq 88(%rsp),%rdi # Pointer to %rip
call early_fixup_exception
andl %eax,%eax
jnz 20f # Found an exception entry
10:
11:
#ifdef CONFIG_EARLY_PRINTK
GET_CR2_INTO(%r9) # can clobber any volatile register if pv
movl 80(%rsp),%r8d # error code
@ -350,7 +391,7 @@ ENTRY(early_idt_handler)
1: hlt
jmp 1b
20: # Exception table entry found
20: # Exception table entry found or page table generated
popq %r11
popq %r10
popq %r9
@ -364,6 +405,8 @@ ENTRY(early_idt_handler)
decl early_recursion_flag(%rip)
INTERRUPT_RETURN
__INITDATA
.balign 4
early_recursion_flag:
.long 0
@ -374,11 +417,10 @@ early_idt_msg:
early_idt_ripmsg:
.asciz "RIP %s\n"
#endif /* CONFIG_EARLY_PRINTK */
.previous
#define NEXT_PAGE(name) \
.balign PAGE_SIZE; \
ENTRY(name)
GLOBAL(name)
/* Automate the creation of 1 to 1 mapping pmd entries */
#define PMDS(START, PERM, COUNT) \
@ -388,24 +430,37 @@ ENTRY(name)
i = i + 1 ; \
.endr
.data
/*
* This default setting generates an ident mapping at address 0x100000
* and a mapping for the kernel that precisely maps virtual address
* 0xffffffff80000000 to physical address 0x000000. (always using
* 2Mbyte large pages provided by PAE mode)
*/
NEXT_PAGE(init_level4_pgt)
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
.org init_level4_pgt + L4_PAGE_OFFSET*8, 0
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
.org init_level4_pgt + L4_START_KERNEL*8, 0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
__INITDATA
NEXT_PAGE(early_level4_pgt)
.fill 511,8,0
.quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
NEXT_PAGE(early_dynamic_pgts)
.fill 512*EARLY_DYNAMIC_PAGE_TABLES,8,0
.data
#ifndef CONFIG_XEN
NEXT_PAGE(init_level4_pgt)
.fill 512,8,0
#else
NEXT_PAGE(init_level4_pgt)
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
.org init_level4_pgt + L4_PAGE_OFFSET*8, 0
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
.org init_level4_pgt + L4_START_KERNEL*8, 0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
.quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
NEXT_PAGE(level3_ident_pgt)
.quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
.fill 511,8,0
.fill 511, 8, 0
NEXT_PAGE(level2_ident_pgt)
/* Since I easily can, map the first 1G.
* Don't set NX because code runs from these pages.
*/
PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD)
#endif
NEXT_PAGE(level3_kernel_pgt)
.fill L3_START_KERNEL,8,0
@ -413,21 +468,6 @@ NEXT_PAGE(level3_kernel_pgt)
.quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE
.quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
NEXT_PAGE(level2_fixmap_pgt)
.fill 506,8,0
.quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
.fill 5,8,0
NEXT_PAGE(level1_fixmap_pgt)
.fill 512,8,0
NEXT_PAGE(level2_ident_pgt)
/* Since I easily can, map the first 1G.
* Don't set NX because code runs from these pages.
*/
PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD)
NEXT_PAGE(level2_kernel_pgt)
/*
* 512 MB kernel mapping. We spend a full page on this pagetable
@ -442,11 +482,16 @@ NEXT_PAGE(level2_kernel_pgt)
PMDS(0, __PAGE_KERNEL_LARGE_EXEC,
KERNEL_IMAGE_SIZE/PMD_SIZE)
NEXT_PAGE(level2_spare_pgt)
.fill 512, 8, 0
NEXT_PAGE(level2_fixmap_pgt)
.fill 506,8,0
.quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
.fill 5,8,0
NEXT_PAGE(level1_fixmap_pgt)
.fill 512,8,0
#undef PMDS
#undef NEXT_PAGE
.data
.align 16
@ -472,6 +517,5 @@ ENTRY(nmi_idt_table)
.skip IDT_ENTRIES * 16
__PAGE_ALIGNED_BSS
.align PAGE_SIZE
ENTRY(empty_zero_page)
NEXT_PAGE(empty_zero_page)
.skip PAGE_SIZE

2
arch/x86/kernel/setup.c
View file

@ -1005,6 +1005,8 @@ void __init setup_arch(char **cmdline_p)
init_mem_mapping();
early_trap_pf_init();
setup_real_mode();
memblock.current_limit = get_max_mapped();

9
arch/x86/kernel/traps.c
View file

@ -688,10 +688,19 @@ void __init early_trap_init(void)
set_intr_gate_ist(X86_TRAP_DB, &debug, DEBUG_STACK);
/* int3 can be called from all */
set_system_intr_gate_ist(X86_TRAP_BP, &int3, DEBUG_STACK);
#ifdef CONFIG_X86_32
set_intr_gate(X86_TRAP_PF, &page_fault);
#endif
load_idt(&idt_descr);
}
void __init early_trap_pf_init(void)
{
#ifdef CONFIG_X86_64
set_intr_gate(X86_TRAP_PF, &page_fault);
#endif
}
void __init trap_init(void)
{
int i;

3
arch/x86/mm/init.c
View file

@ -446,9 +446,10 @@ void __init init_mem_mapping(void)
}
#else
early_ioremap_page_table_range_init();
#endif
load_cr3(swapper_pg_dir);
__flush_tlb_all();
#endif
early_memtest(0, max_pfn_mapped << PAGE_SHIFT);
}