x86/kexec: Eliminate writes through kernel mapping of relocate_kernel page

All writes to the relocate_kernel control page are now done *after* the
%cr3 switch via simple %rip-relative addressing, which means the DATA()
macro with its pointer arithmetic can also now be removed.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20241205153343.3275139-12-dwmw2@infradead.org

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index d52c3bb25b5e64e98999561f36bf055d6baae016..739041c5bca32a9bb40ee5868179077c882090d2 100644 (file)
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -61,21 +61,24 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
        pushq %r15
        pushf
 
-       movq    %rsp, saved_rsp(%rip)
-       movq    %cr0, %rax
-       movq    %rax, saved_cr0(%rip)
-       movq    %cr3, %rax
-       movq    %rax, saved_cr3(%rip)
-       movq    %cr4, %rax
-       movq    %rax, saved_cr4(%rip)
-
-       /* Save CR4. Required to enable the right paging mode later. */
-       movq    %rax, %r13
-
        /* zero out flags, and disable interrupts */
        pushq $0
        popfq
 
+       /* Switch to the identity mapped page tables */
+       movq    %cr3, %rax
+       movq    kexec_pa_table_page(%rip), %r9
+       movq    %r9, %cr3
+
+       /* Save %rsp and CRs. */
+       movq    %rsp, saved_rsp(%rip)
+       movq    %rax, saved_cr3(%rip)
+       movq    %cr0, %rax
+       movq    %rax, saved_cr0(%rip)
+       /* Leave CR4 in %r13 to enable the right paging mode later. */
+       movq    %cr4, %r13
+       movq    %r13, saved_cr4(%rip)
+
        /* Save SME active flag */
        movq    %r8, %r12
 
@@ -85,10 +88,6 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
        /* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
        movq    %rcx, %r11
 
-       /* Switch to the identity mapped page tables */
-       movq    kexec_pa_table_page(%rip), %r9
-       movq    %r9, %cr3
-
        /* Physical address of control page */
        movq    %rsi, %r8