[RFC PATCH v4 04/20] x86/kexec: Only swap pages for preserve_context mode

[David Woodhouse]

From: David Woodhouse <dwmw at amazon.co.uk>

There's no need to swap pages (which involves three memcopies for each
page) in the plain kexec case. Just do a single copy from source to
destination page.

Signed-off-by: David Woodhouse <dwmw at amazon.co.uk>
---
 arch/x86/kernel/relocate_kernel_64.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index fea650f92606..50cc33f2ecb7 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -310,6 +310,9 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
 	movq	%rdi, %rdx    /* Save destination page to %rdx */
 	movq	%rsi, %rax    /* Save source page to %rax */
 
+	testq	%r11, %r11    /* Only actually swap for preserve_context */
+	jz	.Lnoswap
+
 	/* copy source page to swap page */
 	movq	%r10, %rdi
 	movl	$512, %ecx
@@ -324,6 +327,7 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
 	/* copy swap page to destination page */
 	movq	%rdx, %rdi
 	movq	%r10, %rsi
+.Lnoswap:
 	movl	$512, %ecx
 	rep ; movsq
 
-- 
2.47.0