linux-kernel - Re: [patch 00/15] x86/entry: Consolidation

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Date:   Wed, 26 Feb 2020 10:53:19 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [patch 00/15] x86/entry: Consolidation - Part V

On Tue, Feb 25, 2020 at 11:47:19PM +0100, Thomas Gleixner wrote:

>    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git entry-v1-part5

How about the completely untested something below on top to avoid that
silly indirect call on 32bit idtentry.

---
 arch/x86/entry/entry_32.S | 37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index cf94e724743d..c92cd8412ab2 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -723,19 +723,19 @@
 .endm
 
 #ifdef CONFIG_X86_INVD_BUG
-.macro idtentry_push_func vector cfunc
+.macro idtentry_call_func vector cfunc
 	.if \vector == X86_TRAP_XF
 		/* AMD 486 bug: invd from userspace calls exception 19 instead of #GP */
-		ALTERNATIVE "pushl	$exc_general_protection",	\
-			    "pushl	$exc_simd_coprocessor_error",	\
+		ALTERNATIVE "call	exc_general_protection",	\
+			    "call	exc_simd_coprocessor_error",	\
 			    X86_FEATURE_XMM
 	.else
-		pushl $\cfunc
+		call \cfunc
 	.endif
 .endm
 #else
-.macro idtentry_push_func vector cfunc
-	pushl $\cfunc
+.macro idtentry_call_func vector cfunc
+	call \cfunc
 .endm
 #endif
 
@@ -755,10 +755,9 @@ SYM_CODE_START(\asmsym)
 		pushl	$0		/* Clear the error code */
 	.endif
 
-	/* Push the C-function address into the GS slot */
-	idtentry_push_func \vector \cfunc
-	/* Invoke the common exception entry */
-	jmp	common_exception
+	call	common_idtentry
+	idtentry_call_func \vector \cfunc
+	jmp	ret_from_exception
 SYM_CODE_END(\asmsym)
 .endm
 
@@ -1125,7 +1124,6 @@ SYM_FUNC_START(entry_INT80_32)
 .section .fixup, "ax"
 SYM_CODE_START(asm_exc_iret_error)
 	pushl	$0				# no error code
-	pushl	$exc_iret_error
 
 #ifdef CONFIG_DEBUG_ENTRY
 	/*
@@ -1139,7 +1137,9 @@ SYM_CODE_START(asm_exc_iret_error)
 	popl	%eax
 #endif
 
-	jmp	common_exception
+	call	common_idtentry
+	call	exc_iret_error
+	jmp	ret_from_exception
 SYM_CODE_END(asm_exc_iret_error)
 .previous
 	_ASM_EXTABLE(.Lirq_return, asm_exc_iret_error)
@@ -1332,15 +1332,15 @@ SYM_FUNC_START(xen_failsafe_callback)
 SYM_FUNC_END(xen_failsafe_callback)
 #endif /* CONFIG_XEN_PV */
 
-SYM_CODE_START_LOCAL_NOALIGN(common_exception)
-	/* the function address is in %gs's slot on the stack */
+SYM_CODE_START_LOCAL_NOALIGN(common_idtentry)
+	/* the return address is in the %gs stack slot */
 	SAVE_ALL switch_stacks=1 skip_gs=1 unwind_espfix=1
 	ENCODE_FRAME_POINTER
 
 	/* fixup %gs */
 	GS_TO_REG %ecx
-	movl	PT_GS(%esp), %edi		# get the function address
-	REG_TO_PTGS %ecx
+	pushl	PT_GS(%esp)			# push return address
+	REG_TO_OTGS %ecx
 	SET_KERNEL_GS %ecx
 
 	/* fixup orig %eax */
@@ -1348,9 +1348,8 @@ SYM_CODE_START_LOCAL_NOALIGN(common_exception)
 	movl	$-1, PT_ORIG_EAX(%esp)		# no syscall to restart
 
 	movl	%esp, %eax			# pt_regs pointer
-	CALL_NOSPEC %edi
-	jmp	ret_from_exception
-SYM_CODE_END(common_exception)
+	ret
+SYM_CODE_END(common_idtentry)
 
 #ifdef CONFIG_DOUBLEFAULT
 SYM_CODE_START(asm_exc_double_fault)