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x86: kexec: Use one page table in x86_64 machine_kexec
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Impact: reduce kernel BSS size by 7 pages, improve code readability

Two page tables are used in current x86_64 kexec implementation. One
is used to jump from kernel virtual address to identity map address,
the other is used to map all physical memory. In fact, on x86_64,
there is no conflict between kernel virtual address space and physical
memory space, so just one page table is sufficient. The page table
pages used to map control page are dynamically allocated to save
memory if kexec image is not loaded. ASM code used to map control page
is replaced by C code too.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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Huang Ying authored and H. Peter Anvin committed Feb 4, 2009
1 parent c415b3d commit f5deb79
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Showing 3 changed files with 67 additions and 167 deletions.
27 changes: 9 additions & 18 deletions arch/x86/include/asm/kexec.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -9,23 +9,8 @@
# define PAGES_NR 4
#else
# define PA_CONTROL_PAGE 0
# define VA_CONTROL_PAGE 1
# define PA_PGD 2
# define VA_PGD 3
# define PA_PUD_0 4
# define VA_PUD_0 5
# define PA_PMD_0 6
# define VA_PMD_0 7
# define PA_PTE_0 8
# define VA_PTE_0 9
# define PA_PUD_1 10
# define VA_PUD_1 11
# define PA_PMD_1 12
# define VA_PMD_1 13
# define PA_PTE_1 14
# define VA_PTE_1 15
# define PA_TABLE_PAGE 16
# define PAGES_NR 17
# define PA_TABLE_PAGE 1
# define PAGES_NR 2
#endif

#ifdef CONFIG_X86_32
Expand Down Expand Up @@ -157,9 +142,9 @@ relocate_kernel(unsigned long indirection_page,
unsigned long start_address) ATTRIB_NORET;
#endif

#ifdef CONFIG_X86_32
#define ARCH_HAS_KIMAGE_ARCH

#ifdef CONFIG_X86_32
struct kimage_arch {
pgd_t *pgd;
#ifdef CONFIG_X86_PAE
Expand All @@ -169,6 +154,12 @@ struct kimage_arch {
pte_t *pte0;
pte_t *pte1;
};
#else
struct kimage_arch {
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
};
#endif

#endif /* __ASSEMBLY__ */
Expand Down
82 changes: 55 additions & 27 deletions arch/x86/kernel/machine_kexec_64.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,15 +18,6 @@
#include <asm/mmu_context.h>
#include <asm/io.h>

#define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
static u64 kexec_pgd[512] PAGE_ALIGNED;
static u64 kexec_pud0[512] PAGE_ALIGNED;
static u64 kexec_pmd0[512] PAGE_ALIGNED;
static u64 kexec_pte0[512] PAGE_ALIGNED;
static u64 kexec_pud1[512] PAGE_ALIGNED;
static u64 kexec_pmd1[512] PAGE_ALIGNED;
static u64 kexec_pte1[512] PAGE_ALIGNED;

static void init_level2_page(pmd_t *level2p, unsigned long addr)
{
unsigned long end_addr;
Expand Down Expand Up @@ -107,12 +98,65 @@ static int init_level4_page(struct kimage *image, pgd_t *level4p,
return result;
}

static void free_transition_pgtable(struct kimage *image)
{
free_page((unsigned long)image->arch.pud);
free_page((unsigned long)image->arch.pmd);
free_page((unsigned long)image->arch.pte);
}

static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
{
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
unsigned long vaddr, paddr;
int result = -ENOMEM;

vaddr = (unsigned long)relocate_kernel;
paddr = __pa(page_address(image->control_code_page)+PAGE_SIZE);
pgd += pgd_index(vaddr);
if (!pgd_present(*pgd)) {
pud = (pud_t *)get_zeroed_page(GFP_KERNEL);
if (!pud)
goto err;
image->arch.pud = pud;
set_pgd(pgd, __pgd(__pa(pud) | _KERNPG_TABLE));
}
pud = pud_offset(pgd, vaddr);
if (!pud_present(*pud)) {
pmd = (pmd_t *)get_zeroed_page(GFP_KERNEL);
if (!pmd)
goto err;
image->arch.pmd = pmd;
set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
}
pmd = pmd_offset(pud, vaddr);
if (!pmd_present(*pmd)) {
pte = (pte_t *)get_zeroed_page(GFP_KERNEL);
if (!pte)
goto err;
image->arch.pte = pte;
set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
}
pte = pte_offset_kernel(pmd, vaddr);
set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC));
return 0;
err:
free_transition_pgtable(image);
return result;
}


static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
{
pgd_t *level4p;
int result;
level4p = (pgd_t *)__va(start_pgtable);
return init_level4_page(image, level4p, 0, max_pfn << PAGE_SHIFT);
result = init_level4_page(image, level4p, 0, max_pfn << PAGE_SHIFT);
if (result)
return result;
return init_transition_pgtable(image, level4p);
}

static void set_idt(void *newidt, u16 limit)
Expand Down Expand Up @@ -174,7 +218,7 @@ int machine_kexec_prepare(struct kimage *image)

void machine_kexec_cleanup(struct kimage *image)
{
return;
free_transition_pgtable(image);
}

/*
Expand All @@ -195,22 +239,6 @@ void machine_kexec(struct kimage *image)
memcpy(control_page, relocate_kernel, PAGE_SIZE);

page_list[PA_CONTROL_PAGE] = virt_to_phys(control_page);
page_list[VA_CONTROL_PAGE] = (unsigned long)relocate_kernel;
page_list[PA_PGD] = virt_to_phys(&kexec_pgd);
page_list[VA_PGD] = (unsigned long)kexec_pgd;
page_list[PA_PUD_0] = virt_to_phys(&kexec_pud0);
page_list[VA_PUD_0] = (unsigned long)kexec_pud0;
page_list[PA_PMD_0] = virt_to_phys(&kexec_pmd0);
page_list[VA_PMD_0] = (unsigned long)kexec_pmd0;
page_list[PA_PTE_0] = virt_to_phys(&kexec_pte0);
page_list[VA_PTE_0] = (unsigned long)kexec_pte0;
page_list[PA_PUD_1] = virt_to_phys(&kexec_pud1);
page_list[VA_PUD_1] = (unsigned long)kexec_pud1;
page_list[PA_PMD_1] = virt_to_phys(&kexec_pmd1);
page_list[VA_PMD_1] = (unsigned long)kexec_pmd1;
page_list[PA_PTE_1] = virt_to_phys(&kexec_pte1);
page_list[VA_PTE_1] = (unsigned long)kexec_pte1;

page_list[PA_TABLE_PAGE] =
(unsigned long)__pa(page_address(image->control_code_page));

Expand Down
125 changes: 3 additions & 122 deletions arch/x86/kernel/relocate_kernel_64.S
View file
Original file line number Diff line number Diff line change
Expand Up @@ -29,122 +29,6 @@ relocate_kernel:
* %rdx start address
*/

/* map the control page at its virtual address */

movq $0x0000ff8000000000, %r10 /* mask */
mov $(39 - 3), %cl /* bits to shift */
movq PTR(VA_CONTROL_PAGE)(%rsi), %r11 /* address to map */

movq %r11, %r9
andq %r10, %r9
shrq %cl, %r9

movq PTR(VA_PGD)(%rsi), %r8
addq %r8, %r9
movq PTR(PA_PUD_0)(%rsi), %r8
orq $PAGE_ATTR, %r8
movq %r8, (%r9)

shrq $9, %r10
sub $9, %cl

movq %r11, %r9
andq %r10, %r9
shrq %cl, %r9

movq PTR(VA_PUD_0)(%rsi), %r8
addq %r8, %r9
movq PTR(PA_PMD_0)(%rsi), %r8
orq $PAGE_ATTR, %r8
movq %r8, (%r9)

shrq $9, %r10
sub $9, %cl

movq %r11, %r9
andq %r10, %r9
shrq %cl, %r9

movq PTR(VA_PMD_0)(%rsi), %r8
addq %r8, %r9
movq PTR(PA_PTE_0)(%rsi), %r8
orq $PAGE_ATTR, %r8
movq %r8, (%r9)

shrq $9, %r10
sub $9, %cl

movq %r11, %r9
andq %r10, %r9
shrq %cl, %r9

movq PTR(VA_PTE_0)(%rsi), %r8
addq %r8, %r9
movq PTR(PA_CONTROL_PAGE)(%rsi), %r8
orq $PAGE_ATTR, %r8
movq %r8, (%r9)

/* identity map the control page at its physical address */

movq $0x0000ff8000000000, %r10 /* mask */
mov $(39 - 3), %cl /* bits to shift */
movq PTR(PA_CONTROL_PAGE)(%rsi), %r11 /* address to map */

movq %r11, %r9
andq %r10, %r9
shrq %cl, %r9

movq PTR(VA_PGD)(%rsi), %r8
addq %r8, %r9
movq PTR(PA_PUD_1)(%rsi), %r8
orq $PAGE_ATTR, %r8
movq %r8, (%r9)

shrq $9, %r10
sub $9, %cl

movq %r11, %r9
andq %r10, %r9
shrq %cl, %r9

movq PTR(VA_PUD_1)(%rsi), %r8
addq %r8, %r9
movq PTR(PA_PMD_1)(%rsi), %r8
orq $PAGE_ATTR, %r8
movq %r8, (%r9)

shrq $9, %r10
sub $9, %cl

movq %r11, %r9
andq %r10, %r9
shrq %cl, %r9

movq PTR(VA_PMD_1)(%rsi), %r8
addq %r8, %r9
movq PTR(PA_PTE_1)(%rsi), %r8
orq $PAGE_ATTR, %r8
movq %r8, (%r9)

shrq $9, %r10
sub $9, %cl

movq %r11, %r9
andq %r10, %r9
shrq %cl, %r9

movq PTR(VA_PTE_1)(%rsi), %r8
addq %r8, %r9
movq PTR(PA_CONTROL_PAGE)(%rsi), %r8
orq $PAGE_ATTR, %r8
movq %r8, (%r9)

relocate_new_kernel:
/* %rdi indirection_page
* %rsi page_list
* %rdx start address
*/

/* zero out flags, and disable interrupts */
pushq $0
popfq
Expand All @@ -156,9 +40,8 @@ relocate_new_kernel:
/* get physical address of page table now too */
movq PTR(PA_TABLE_PAGE)(%rsi), %rcx

/* switch to new set of page tables */
movq PTR(PA_PGD)(%rsi), %r9
movq %r9, %cr3
/* Switch to the identity mapped page tables */
movq %rcx, %cr3

/* setup a new stack at the end of the physical control page */
lea PAGE_SIZE(%r8), %rsp
Expand Down Expand Up @@ -194,9 +77,7 @@ identity_mapped:
jmp 1f
1:

/* Switch to the identity mapped page tables,
* and flush the TLB.
*/
/* Flush the TLB (needed?) */
movq %rcx, %cr3

/* Do the copies */
Expand Down

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