linux-kernel - [RFC PATCH v4 13/20] x86/kexec: Clean up register usage in relocate

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Message-ID: <20241127190343.44916-14-dwmw2@infradead.org>
Date: Wed, 27 Nov 2024 19:00:27 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: kexec@...ts.infradead.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	linux-kernel@...r.kernel.org,
	Simon Horman <horms@...nel.org>,
	Dave Young <dyoung@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	jpoimboe@...nel.org,
	bsz@...zon.de
Subject: [RFC PATCH v4 13/20] x86/kexec: Clean up register usage in relocate_kernel()

From: David Woodhouse <dwmw@...zon.co.uk>

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@...zon.co.uk>
---
 arch/x86/kernel/relocate_kernel_64.S | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 288dfc08c63d..b24198eb1fe9 100644
--- 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:
-- 
2.47.0