Commit 207bdf7f authored by David Woodhouse's avatar David Woodhouse Committed by Ingo Molnar
Browse files

x86/kexec: Clean up and document register use in relocate_kernel_64.S 



Add more comments explaining what each register contains, and save the
preserve_context flag to a non-clobbered register sooner, to keep things
simpler.

No change in behavior intended.

Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarKai Huang <kai.huang@intel.com>
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/20241205153343.3275139-3-dwmw2@infradead.org
parent fe8ec69b

arch/x86/kernel/relocate_kernel_64.S

+14 −4
Original line number Diff line number Diff line
@@ -100,6 +100,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel) 
	movq	%r10, CP_PA_SWAP_PAGE(%r11)

	movq	%rdi, CP_PA_BACKUP_PAGES_MAP(%r11)



	/* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */

	movq	%rcx, %r11



	/* Switch to the identity mapped page tables */

	movq	%r9, %cr3
@@ -116,6 +119,14 @@ SYM_CODE_END(relocate_kernel) 


SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)

	UNWIND_HINT_END_OF_STACK

	/*

	 * %rdi	indirection page

	 * %rdx start address

	 * %r11 preserve_context

	 * %r12 host_mem_enc_active

	 * %r13 original CR4 when relocate_kernel() was invoked

	 */



	/* set return address to 0 if not preserving context */

	pushq	$0

	/* store the start address on the stack */
@@ -170,8 +181,6 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) 
	wbinvd

.Lsme_off:



	/* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */

	movq	%rcx, %r11

	call	swap_pages



	/*
@@ -183,13 +192,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) 
	movq	%cr3, %rax

	movq	%rax, %cr3



	testq	%r11, %r11	/* preserve_context */

	jnz .Lrelocate



	/*

	 * set all of the registers to known values

	 * leave %rsp alone

	 */



	testq	%r11, %r11

	jnz .Lrelocate

	xorl	%eax, %eax

	xorl	%ebx, %ebx

	xorl    %ecx, %ecx