[PATCH AUTOSEL 5.18 28/41] x86/xen: Use clear_bss() for Xen PV guests

[Sasha Levin]

From: Juergen Gross <jgross@xxxxxxxx>

[ Upstream commit 96e8fc5818686d4a1591bb6907e7fdb64ef29884 ]

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@xxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220630071441.28576-2-jgross@xxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 896e48d45828..bccc84de7ff2 100644
--- 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 align);
 	}
 
 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 4f5ecbbaae77..2e10a33778cf 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -421,7 +421,7 @@ 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 5038edb79ad5..b55de4ad685c 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
-- 
2.35.1