linux-kernel - [PATCH v3 1/3] x86/xen: use clear

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Date:   Thu, 30 Jun 2022 09:14:39 +0200
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     jpoimboe@...nel.org, Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Jan Beulich <jbeulich@...e.com>
Subject: [PATCH v3 1/3] x86/xen: use clear_bss() for Xen PV guests

Instead of clearing the bss area in assembly code, use the clear_bss()
function.

This requires to pass the start_info address as parameter to
xen_start_kernel() in order to avoid the xen_start_info being zeroed
again.

Signed-off-by: Juergen Gross <jgross@...e.com>
Reviewed-by: Jan Beulich <jbeulich@...e.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
---
 arch/x86/include/asm/setup.h |  3 +++
 arch/x86/kernel/head64.c     |  2 +-
 arch/x86/xen/enlighten_pv.c  |  8 ++++++--
 arch/x86/xen/xen-head.S      | 10 +---------
 4 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index f8b9ee97a891..f37cbff7354c 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -120,6 +120,9 @@ void *extend_brk(size_t size, size_t align);
 	static char __brk_##name[size]
 
 extern void probe_roms(void);
+
+void clear_bss(void);
+
 #ifdef __i386__
 
 asmlinkage void __init i386_start_kernel(void);
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index bd4a34100ed0..e7e233209a8c 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -426,7 +426,7 @@ void __init do_early_exception(struct pt_regs *regs, int trapnr)
 
 /* Don't add a printk in there. printk relies on the PDA which is not initialized 
    yet. */
-static void __init clear_bss(void)
+void __init clear_bss(void)
 {
 	memset(__bss_start, 0,
 	       (unsigned long) __bss_stop - (unsigned long) __bss_start);
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index e3297b15701c..70fb2ea85e90 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1183,15 +1183,19 @@ static void __init xen_domu_set_legacy_features(void)
 extern void early_xen_iret_patch(void);
 
 /* First C function to be called on Xen boot */
-asmlinkage __visible void __init xen_start_kernel(void)
+asmlinkage __visible void __init xen_start_kernel(struct start_info *si)
 {
 	struct physdev_set_iopl set_iopl;
 	unsigned long initrd_start = 0;
 	int rc;
 
-	if (!xen_start_info)
+	if (!si)
 		return;
 
+	clear_bss();
+
+	xen_start_info = si;
+
 	__text_gen_insn(&early_xen_iret_patch,
 			JMP32_INSN_OPCODE, &early_xen_iret_patch, &xen_iret,
 			JMP32_INSN_SIZE);
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 3a2cd93bf059..13af6fe453e3 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -48,15 +48,6 @@ SYM_CODE_START(startup_xen)
 	ANNOTATE_NOENDBR
 	cld
 
-	/* Clear .bss */
-	xor %eax,%eax
-	mov $__bss_start, %rdi
-	mov $__bss_stop, %rcx
-	sub %rdi, %rcx
-	shr $3, %rcx
-	rep stosq
-
-	mov %rsi, xen_start_info
 	mov initial_stack(%rip), %rsp
 
 	/* Set up %gs.
@@ -71,6 +62,7 @@ SYM_CODE_START(startup_xen)
 	cdq
 	wrmsr
 
+	mov	%rsi, %rdi
 	call xen_start_kernel
 SYM_CODE_END(startup_xen)
 	__FINIT
-- 
2.35.3