From: David Woodhouse <dwmw@amazon.co.uk>
Date: Thu, 5 Dec 2024 15:05:10 +0000 (+0000)
Subject: x86/kexec: Only swap pages for ::preserve_context mode
X-Git-Tag: v6.14-rc1~119^2~23
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=9e5683e2d0b5584c51993908c5d0afa78e613492;p=thirdparty%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>
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/20241205153343.3275139-5-dwmw2@infradead.org
---

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index fea650f926066..ca7f1e1d5b114 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