x86/kexec: Add data section to relocate_kernel

Now that it's handled sanely by a linker script we can have actual data,
and just use %rip-relative addressing to access it.

If we could call the *copy* instead of the original relocate_kernel in
the kernel text, then we could use %rip-relative addressing everywhere.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 1efcbd340528693cf735ca89b97a10c319659e49..ad303396bee36c688064717e8ff37f116513d044 100644 (file)
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -27,18 +27,28 @@
  * ~ control_page + PAGE_SIZE are used as data storage and stack for
  * jumping back
  */
-#define DATA(offset)           (KEXEC_CONTROL_CODE_MAX_SIZE+(offset))
 
+       .section .data.relocate_kernel,"a";
 /* Minimal CPU state */
-#define RSP                    DATA(0x0)
-#define CR0                    DATA(0x8)
-#define CR3                    DATA(0x10)
-#define CR4                    DATA(0x18)
-
+SYM_DATA_LOCAL(saved_rsp, .quad 0)
+SYM_DATA_LOCAL(saved_cr0, .quad 0)
+SYM_DATA_LOCAL(saved_cr3, .quad 0)
+SYM_DATA_LOCAL(saved_cr4, .quad 0)
 /* other data */
-#define CP_PA_TABLE_PAGE       DATA(0x20)
-#define CP_PA_SWAP_PAGE                DATA(0x28)
-#define CP_PA_BACKUP_PAGES_MAP DATA(0x30)
+SYM_DATA_LOCAL(pa_table_page, .quad 0)
+SYM_DATA_LOCAL(pa_swap_page, .quad 0)
+SYM_DATA_LOCAL(pa_backup_pages_map, .quad 0)
+
+/*
+ * There are two physical copies of relocate_kernel(), one in the original
+ * Kernel text and the other copied to the control page. There is a virtual
+ * mapping of each, in the original kernel. It is the *original* which is
+ * called from machine_kexec(), largely becaose the copy isn't mapped as an
+ * executable page. Thus, this code cannot just use %rip-relative addressing
+ * until after the %cr3 change and the jump to identity_mapped(). Until
+ * then, some pointer arithmetic is required.
+ */
+#define DATA(x) (x - relocate_kernel)
 
        .section .text.relocate_kernel,"ax";
        .code64
@@ -63,13 +73,13 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
        pushf
 
        movq    PTR(VA_CONTROL_PAGE)(%rsi), %r11
-       movq    %rsp, RSP(%r11)
+       movq    %rsp, DATA(saved_rsp)(%r11)
        movq    %cr0, %rax
-       movq    %rax, CR0(%r11)
+       movq    %rax, DATA(saved_cr0)(%r11)
        movq    %cr3, %rax
-       movq    %rax, CR3(%r11)
+       movq    %rax, DATA(saved_cr3)(%r11)
        movq    %cr4, %rax
-       movq    %rax, CR4(%r11)
+       movq    %rax, DATA(saved_cr4)(%r11)
 
        /* Save CR4. Required to enable the right paging mode later. */
        movq    %rax, %r13
@@ -94,9 +104,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
        movq    PTR(PA_SWAP_PAGE)(%rsi), %r10
 
        /* save some information for jumping back */
-       movq    %r9, CP_PA_TABLE_PAGE(%r11)
-       movq    %r10, CP_PA_SWAP_PAGE(%r11)
-       movq    %rdi, CP_PA_BACKUP_PAGES_MAP(%r11)
+       movq    %r9, DATA(pa_table_page)(%r11)
+       movq    %r10, DATA(pa_swap_page)(%r11)
+       movq    %rdi, DATA(pa_backup_pages_map)(%r11)
 
        /* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
        movq    %rcx, %r11
@@ -227,9 +237,9 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
        /* get the re-entry point of the peer system */
        movq    0(%rsp), %rbp
        leaq    relocate_kernel(%rip), %r8
-       movq    CP_PA_SWAP_PAGE(%r8), %r10
-       movq    CP_PA_BACKUP_PAGES_MAP(%r8), %rdi
-       movq    CP_PA_TABLE_PAGE(%r8), %rax
+       movq    pa_swap_page(%rip), %r10
+       movq    pa_backup_pages_map(%rip), %rdi
+       movq    pa_table_page(%rip), %rax
        movq    %rax, %cr3
        lea     PAGE_SIZE(%r8), %rsp
        call    swap_pages
@@ -243,11 +253,11 @@ SYM_CODE_END(identity_mapped)
 SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
        UNWIND_HINT_END_OF_STACK
        ANNOTATE_NOENDBR // RET target, above
-       movq    RSP(%r8), %rsp
-       movq    CR4(%r8), %rax
+       movq    saved_rsp(%rip), %rsp
+       movq    saved_cr4(%rip), %rax
        movq    %rax, %cr4
-       movq    CR3(%r8), %rax
-       movq    CR0(%r8), %r8
+       movq    saved_cr3(%rip), %rax
+       movq    saved_cr0(%r8), %r8
        movq    %rax, %cr3
        movq    %r8, %cr0
        movq    %rbp, %rax

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ad451371e1794ca2cc1fcfb724e26327c073723b..65f879b31a825223378b2d287e3f3bd30ef76b87 100644 (file)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -100,7 +100,7 @@ const_pcpu_hot = pcpu_hot;
        . = ALIGN(PAGE_SIZE);                                   \
        __relocate_kernel_start = .;                            \
        *(.text.relocate_kernel);                               \
-       *(.rodata.relocate_kernel);                             \
+       *(.data.relocate_kernel);                               \
        __relocate_kernel_end = .;
 #else
 #define KEXEC_RELOCATE_KERNEL_TEXT