x86: kexec: Use one page table in x86_64 machine_kexec

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>

1 files changed, 3 insertions, 122 deletions

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index f5afe66..b0bbdd4 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -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
@@ -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
@@ -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 */