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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Juergen Gross <jgross@suse.com>,
        Borislav Petkov <bp@suse.de>, Jan Beulich <jbeulich@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: [PATCH 5.18 006/231] x86/xen: Use clear_bss() for Xen PV guests
Date:   Tue, 19 Jul 2022 13:51:31 +0200
Message-Id: <20220719114714.704934047@linuxfoundation.org>
In-Reply-To: <20220719114714.247441733@linuxfoundation.org>
References: <20220719114714.247441733@linuxfoundation.org>
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From: Juergen Gross <jgross@suse.com>

commit 96e8fc5818686d4a1591bb6907e7fdb64ef29884 upstream.

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@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20220630071441.28576-2-jgross@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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(-)

--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -132,6 +132,9 @@ void *extend_brk(size_t size, size_t ali
 	}
 
 extern void probe_roms(void);
+
+void clear_bss(void);
+
 #ifdef __i386__
 
 asmlinkage void __init i386_start_kernel(void);
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -421,7 +421,7 @@ void __init do_early_exception(struct pt
 
 /* 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);
--- 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_f
 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);
--- 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