x86/kexec: Clean up register usage in relocate_kernel()

The memory encryption flag is passed in %r8 because that's where the
calling convention puts it. Instead of moving it to %r12 and then using
%r8 for other things, just leave it in %r8 and use other registers
instead.

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/20241205153343.3275139-13-dwmw2@infradead.org

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 739041c5bca32a9bb40ee5868179077c882090d2..8bc86a1e056a70a56038888077833eb3f037d6c6 100644 (file)
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -79,24 +79,18 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
        movq    %cr4, %r13
        movq    %r13, saved_cr4(%rip)
 
-       /* Save SME active flag */
-       movq    %r8, %r12
-
        /* save indirection list for jumping back */
        movq    %rdi, pa_backup_pages_map(%rip)
 
        /* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
        movq    %rcx, %r11
 
-       /* Physical address of control page */
-       movq    %rsi, %r8
-
        /* setup a new stack at the end of the physical control page */
-       lea     PAGE_SIZE(%r8), %rsp
+       lea     PAGE_SIZE(%rsi), %rsp
 
        /* jump to identity mapped page */
-       addq    $(identity_mapped - relocate_kernel), %r8
-       pushq   %r8
+       addq    $(identity_mapped - relocate_kernel), %rsi
+       pushq   %rsi
        ANNOTATE_UNRET_SAFE
        ret
        int3
@@ -107,8 +101,9 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
        /*
         * %rdi indirection page
         * %rdx start address
+        * %r8 host_mem_enc_active
+        * %r9 page table page
         * %r11 preserve_context
-        * %r12 host_mem_enc_active
         * %r13 original CR4 when relocate_kernel() was invoked
         */
 
@@ -161,7 +156,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
         * entries that will conflict with the now unencrypted memory
         * used by kexec. Flush the caches before copying the kernel.
         */
-       testq   %r12, %r12
+       testq   %r8, %r8
        jz .Lsme_off
        wbinvd
 .Lsme_off: