[Xen-devel] [PATCH] x86: streamline page fault path

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

#PF is, in all "normal" usage models, the only potentially high
frequency (and hence performance sensitive) exception. Thus make it
the fall-through case into handle_exception (rather than
divide_error for x86-32 and not having one at all for x86-64).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- a/xen/arch/x86/x86_32/entry.S
+++ b/xen/arch/x86/x86_32/entry.S
@@ -438,9 +438,8 @@ ENTRY(ret_from_intr)
         jnz   test_all_events
         jmp   restore_all_xen
 
-ENTRY(divide_error)
-        pushl $TRAP_divide_error<<16
-        ALIGN
+ENTRY(page_fault)
+        movw  $TRAP_page_fault,2(%esp)
 handle_exception:
         FIXUP_RING0_GUEST_STACK
         SAVE_ALL(1f,2f)
@@ -513,6 +512,10 @@ ENTRY(device_not_available)
         pushl $TRAP_no_device<<16
         jmp   handle_exception
 
+ENTRY(divide_error)
+        pushl $TRAP_divide_error<<16
+        jmp   handle_exception
+
 ENTRY(debug)
         pushl $TRAP_debug<<16
         jmp   handle_exception
@@ -557,10 +560,6 @@ ENTRY(alignment_check)
         movw  $TRAP_alignment_check,2(%esp)
         jmp   handle_exception
 
-ENTRY(page_fault)
-        movw  $TRAP_page_fault,2(%esp)
-        jmp   handle_exception
-
 ENTRY(spurious_interrupt_bug)
         pushl $TRAP_spurious_int<<16
         jmp   handle_exception
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -474,9 +474,11 @@ ENTRY(ret_from_intr)
         jz    test_all_events
         jmp   compat_test_all_events
 
-        ALIGN
+ENTRY(page_fault)
+        movl  $TRAP_page_fault,4(%rsp)
 /* No special register assumptions. */
-ENTRY(handle_exception)
+       .globl handle_exception
+handle_exception:
         SAVE_ALL
 handle_exception_saved:
         testb $X86_EFLAGS_IF>>8,UREGS_eflags+1(%rsp)
@@ -598,10 +600,6 @@ ENTRY(alignment_check)
         movl  $TRAP_alignment_check,4(%rsp)
         jmp   handle_exception
 
-ENTRY(page_fault)
-        movl  $TRAP_page_fault,4(%rsp)
-        jmp   handle_exception
-
 ENTRY(spurious_interrupt_bug)
         pushq $0
         movl  $TRAP_spurious_int,4(%rsp)

Attachment: x86-prefer-page-fault.patch
Description: Text document

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