From: David Woodhouse <dwmw@amazon.co.uk>
Date: Sat, 2 Nov 2024 23:27:33 +0000 (+0000)
Subject: x86/kexec: Only swap pages for preserve_context mode
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=496fd4967a2097b38c0ec536c8527568bc2dfef0;p=users%2Fdwmw2%2Flinux.git

x86/kexec: Only swap pages for preserve_context mode

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@amazon.co.uk>
---

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index ca01e3e2f097c..2848d086ceb0f 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -303,6 +303,9 @@ 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 */
+	jnz .Lnoswap
+
 	/* copy source page to swap page */
 	movq	%r10, %rdi
 	movl	$512, %ecx
@@ -317,6 +320,7 @@ 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