[PATCH v5 3/9] x86/head: Move early exception panic code into early_fixup_exception

From: Andy Lutomirski <luto@kernel.org>
To: X86 ML <x86@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	KVM list <kvm@vger.kernel.org>,
	Arjan van de Ven <arjan@linux.intel.com>,
	xen-devel <Xen-devel@lists.xen.org>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>
Subject: [PATCH v5 3/9] x86/head: Move early exception panic code into early_fixup_exception
Date: Sat,  2 Apr 2016 07:01:34 -0700	[thread overview]
Message-ID: <4085070316fc3ab29538d3fcfe282648d1d4ee2e.1459605520.git.luto@kernel.org> (raw)
In-Reply-To: <cover.1459605520.git.luto@kernel.org>
In-Reply-To: <cover.1459605520.git.luto@kernel.org>

This removes a bunch of assembly and adds some C code instead.  It
changes the actual printouts on both 32-bit and 64-bit kernels, but
they still seem okay.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/uaccess.h |  2 +-
 arch/x86/kernel/head_32.S      | 49 +++++-------------------------------------
 arch/x86/kernel/head_64.S      | 45 ++------------------------------------
 arch/x86/mm/extable.c          | 29 ++++++++++++++++++++-----
 4 files changed, 32 insertions(+), 93 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a3afb7259751..83fd2cf187d2 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -111,7 +111,7 @@ struct exception_table_entry {
 
 extern int fixup_exception(struct pt_regs *regs, int trapnr);
 extern bool ex_has_fault_handler(unsigned long ip);
-extern int early_fixup_exception(struct pt_regs *regs, int trapnr);
+extern void early_fixup_exception(struct pt_regs *regs, int trapnr);
 
 /*
  * These are the main single-value transfer routines.  They automatically
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 5e6ce845813a..411dce93fee9 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -555,8 +555,6 @@ early_idt_handler_common:
 	 */
 	cld
 
-	cmpl $2,%ss:early_recursion_flag
-	je hlt_loop
 	incl %ss:early_recursion_flag
 
 	/* The vector number is in pt_regs->gs */
@@ -588,13 +586,8 @@ early_idt_handler_common:
 	movw	%gs, PT_GS(%esp)
 	movw	$0, PT_GS+2(%esp)
 
-	cmpl $(__KERNEL_CS),PT_CS(%esp)
-	jne 10f
-
 	movl	%esp, %eax	/* args are pt_regs (EAX), trapnr (EDX) */
 	call	early_fixup_exception
-	andl	%eax,%eax
-	jz	10f		/* Exception wasn't fixed up */
 
 	popl	%ebx		/* pt_regs->bx */
 	popl	%ecx		/* pt_regs->cx */
@@ -610,29 +603,6 @@ early_idt_handler_common:
 	decl	%ss:early_recursion_flag
 	addl	$4, %esp	/* pop pt_regs->orig_ax */
 	iret
-
-10:
-#ifdef CONFIG_PRINTK
-	xorl %eax,%eax
-	movw %ax,PT_FS+2(%esp)	/* clean up the segment values on some cpus */
-	movw %ax,PT_DS+2(%esp)
-	movw %ax,PT_ES+2(%esp)
-	leal  40(%esp),%eax
-	pushl %eax		/* %esp before the exception */
-	pushl %ebx
-	pushl %ebp
-	pushl %esi
-	pushl %edi
-	movl %cr2,%eax
-	pushl %eax
-	pushl (20+6*4)(%esp)	/* trapno */
-	pushl $fault_msg
-	call printk
-#endif
-	call dump_stack
-hlt_loop:
-	hlt
-	jmp hlt_loop
 ENDPROC(early_idt_handler_common)
 
 /* This is the default interrupt "handler" :-) */
@@ -668,10 +638,14 @@ ignore_int:
 	popl %eax
 #endif
 	iret
+
+hlt_loop:
+	hlt
+	jmp hlt_loop
 ENDPROC(ignore_int)
 __INITDATA
 	.align 4
-early_recursion_flag:
+GLOBAL(early_recursion_flag)
 	.long 0
 
 __REFDATA
@@ -736,19 +710,6 @@ __INITRODATA
 int_msg:
 	.asciz "Unknown interrupt or fault at: %p %p %p\n"
 
-fault_msg:
-/* fault info: */
-	.ascii "BUG: Int %d: CR2 %p\n"
-/* regs pushed in early_idt_handler: */
-	.ascii "     EDI %p  ESI %p  EBP %p  EBX %p\n"
-	.ascii "     ESP %p   ES %p   DS %p\n"
-	.ascii "     EDX %p  ECX %p  EAX %p\n"
-/* fault frame: */
-	.ascii "     vec %p  err %p  EIP %p   CS %p  flg %p\n"
-	.ascii "Stack: %p %p %p %p %p %p %p %p\n"
-	.ascii "       %p %p %p %p %p %p %p %p\n"
-	.asciz "       %p %p %p %p %p %p %p %p\n"
-
 #include "../../x86/xen/xen-head.S"
 
 /*
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index af87896b6a23..c39b6437cf03 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -354,8 +354,6 @@ early_idt_handler_common:
 	 */
 	cld
 
-	cmpl $2,early_recursion_flag(%rip)
-	jz  1f
 	incl early_recursion_flag(%rip)
 
 	/* The vector number is currently in the pt_regs->di slot. */
@@ -376,9 +374,6 @@ early_idt_handler_common:
 	pushq %r14				/* pt_regs->r14 */
 	pushq %r15				/* pt_regs->r15 */
 
-	cmpl $__KERNEL_CS,CS(%rsp)
-	jne 11f
-
 	cmpq $14,%rsi		/* Page fault? */
 	jnz 10f
 	GET_CR2_INTO(%rdi)	/* Can clobber any volatile register if pv */
@@ -389,37 +384,8 @@ early_idt_handler_common:
 10:
 	movq %rsp,%rdi		/* RDI = pt_regs; RSI is already trapnr */
 	call early_fixup_exception
-	andl %eax,%eax
-	jnz 20f			# Found an exception entry
-
-11:
-#ifdef CONFIG_EARLY_PRINTK
-	/*
-	 * On paravirt kernels, GET_CR2_INTO clobbers callee-clobbered regs.
-	 * We only care about RSI, so we need to save it.
-	 */
-	movq %rsi,%rbx		/* Save vector number */
-	GET_CR2_INTO(%r9)
-	movq ORIG_RAX(%rsp),%r8	/* error code */
-	movq %rbx,%rsi		/* vector number */
-	movq CS(%rsp),%rdx
-	movq RIP(%rsp),%rcx
-	xorl %eax,%eax
-	leaq early_idt_msg(%rip),%rdi
-	call early_printk
-	cmpl $2,early_recursion_flag(%rip)
-	jz  1f
-	call dump_stack
-#ifdef CONFIG_KALLSYMS	
-	leaq early_idt_ripmsg(%rip),%rdi
-	movq RIP(%rsp),%rsi	# %rip again
-	call __print_symbol
-#endif
-#endif /* EARLY_PRINTK */
-1:	hlt
-	jmp 1b
 
-20:	/* Exception table entry found or page table generated */
+20:
 	decl early_recursion_flag(%rip)
 	jmp restore_regs_and_iret
 ENDPROC(early_idt_handler_common)
@@ -427,16 +393,9 @@ ENDPROC(early_idt_handler_common)
 	__INITDATA
 
 	.balign 4
-early_recursion_flag:
+GLOBAL(early_recursion_flag)
 	.long 0
 
-#ifdef CONFIG_EARLY_PRINTK
-early_idt_msg:
-	.asciz "PANIC: early exception %02lx rip %lx:%lx error %lx cr2 %lx\n"
-early_idt_ripmsg:
-	.asciz "RIP %s\n"
-#endif /* CONFIG_EARLY_PRINTK */
-
 #define NEXT_PAGE(name) \
 	.balign	PAGE_SIZE; \
 GLOBAL(name)
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index d6e4e6fb4002..8997022abebc 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -90,8 +90,10 @@ int fixup_exception(struct pt_regs *regs, int trapnr)
 	return handler(e, regs, trapnr);
 }
 
+extern unsigned int early_recursion_flag;
+
 /* Restricted version used during very early boot */
-int __init early_fixup_exception(struct pt_regs *regs, int trapnr)
+void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
 {
 	const struct exception_table_entry *e;
 	unsigned long new_ip;
@@ -99,21 +101,38 @@ int __init early_fixup_exception(struct pt_regs *regs, int trapnr)
 
 	/* Ignore early NMIs. */
 	if (trapnr == X86_TRAP_NMI)
-		return 1;
+		return;
+
+	if (early_recursion_flag > 2)
+		goto halt_loop;
+
+	if (regs->cs != __KERNEL_CS)
+		goto fail;
 
 	e = search_exception_tables(regs->ip);
 	if (!e)
-		return 0;
+		goto fail;
 
 	new_ip  = ex_fixup_addr(e);
 	handler = ex_fixup_handler(e);
 
 	/* special handling not supported during early boot */
 	if (handler != ex_handler_default)
-		return 0;
+		goto fail;
 
 	regs->ip = new_ip;
-	return 1;
+	return;
+
+fail:
+	early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
+		     (unsigned)trapnr, (unsigned long)regs->cs, regs->ip,
+		     regs->orig_ax, read_cr2());
+
+	show_regs(regs);
+
+halt_loop:
+	while (true)
+		halt();
 }
 
 /*
-- 
2.5.5
