x86/entry: re-order exception entry points

Commit Message

Jan Beulich March 6, 2024, 1:57 p.m. UTC

Arrange for Disp8 JMPs to be usable. On top of the MOVL->MOVB conversion
this further reduces entry point size, such that in particular INT3 (for
guarding against straight line speculation) would then also still fit
within the same 16-byte block, irrespective of CET-IBT being enabled. Of
course when CC_SPLIT_SECTIONS=y the ordering here doesn't matter at all.

Which of the non-IST exception entry points are moved is based on
presumed / guessed frequency of use.

Signed-off-by: Jan Beulich <[e-mail]>
---
Arguably we could move all these entry points ahead of handle_exception,
accepting that the first few will continue to use Disp32 JMPs.

Patch

--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -725,6 +725,59 @@  FUNC(common_interrupt)
         jmp ret_from_intr
 END(common_interrupt)
 
+FUNC(entry_BP)
+        ENDBR64
+        pushq $0
+        movb  $X86_EXC_BP, EFRAME_entry_vector(%rsp)
+        jmp   handle_exception
+END(entry_BP)
+
+FUNC(entry_SS)
+        ENDBR64
+        movb  $X86_EXC_SS, EFRAME_entry_vector(%rsp)
+        jmp   handle_exception
+END(entry_SS)
+
+FUNC(entry_AC)
+        ENDBR64
+        movb  $X86_EXC_AC, EFRAME_entry_vector(%rsp)
+        jmp   handle_exception
+END(entry_AC)
+
+FUNC(entry_NM)
+        ENDBR64
+        pushq $0
+        movb  $X86_EXC_NM, EFRAME_entry_vector(%rsp)
+        jmp   handle_exception
+END(entry_NM)
+
+FUNC(entry_MF)
+        ENDBR64
+        pushq $0
+        movb  $X86_EXC_MF, EFRAME_entry_vector(%rsp)
+        jmp   handle_exception
+END(entry_MF)
+
+FUNC(entry_XM)
+        ENDBR64
+        pushq $0
+        movb  $X86_EXC_XM, EFRAME_entry_vector(%rsp)
+        jmp   handle_exception
+END(entry_XM)
+
+FUNC(entry_UD)
+        ENDBR64
+        pushq $0
+        movb  $X86_EXC_UD, EFRAME_entry_vector(%rsp)
+        jmp   handle_exception
+END(entry_UD)
+
+FUNC(entry_GP)
+        ENDBR64
+        movb  $X86_EXC_GP, EFRAME_entry_vector(%rsp)
+        jmp   handle_exception
+END(entry_GP)
+
 FUNC(entry_PF)
         ENDBR64
         movb  $X86_EXC_PF, EFRAME_entry_vector(%rsp)
@@ -908,41 +961,6 @@  FUNC(entry_DE)
         jmp   handle_exception
 END(entry_DE)
 
-FUNC(entry_MF)
-        ENDBR64
-        pushq $0
-        movb  $X86_EXC_MF, EFRAME_entry_vector(%rsp)
-        jmp   handle_exception
-END(entry_MF)
-
-FUNC(entry_XM)
-        ENDBR64
-        pushq $0
-        movb  $X86_EXC_XM, EFRAME_entry_vector(%rsp)
-        jmp   handle_exception
-END(entry_XM)
-
-FUNC(entry_NM)
-        ENDBR64
-        pushq $0
-        movb  $X86_EXC_NM, EFRAME_entry_vector(%rsp)
-        jmp   handle_exception
-END(entry_NM)
-
-FUNC(entry_DB)
-        ENDBR64
-        pushq $0
-        movb  $X86_EXC_DB, EFRAME_entry_vector(%rsp)
-        jmp   handle_ist_exception
-END(entry_DB)
-
-FUNC(entry_BP)
-        ENDBR64
-        pushq $0
-        movb  $X86_EXC_BP, EFRAME_entry_vector(%rsp)
-        jmp   handle_exception
-END(entry_BP)
-
 FUNC(entry_OF)
         ENDBR64
         pushq $0
@@ -957,13 +975,6 @@  FUNC(entry_BR)
         jmp   handle_exception
 END(entry_BR)
 
-FUNC(entry_UD)
-        ENDBR64
-        pushq $0
-        movb  $X86_EXC_UD, EFRAME_entry_vector(%rsp)
-        jmp   handle_exception
-END(entry_UD)
-
 FUNC(entry_TS)
         ENDBR64
         movb  $X86_EXC_TS, EFRAME_entry_vector(%rsp)
@@ -976,24 +987,6 @@  FUNC(entry_NP)
         jmp   handle_exception
 END(entry_NP)
 
-FUNC(entry_SS)
-        ENDBR64
-        movb  $X86_EXC_SS, EFRAME_entry_vector(%rsp)
-        jmp   handle_exception
-END(entry_SS)
-
-FUNC(entry_GP)
-        ENDBR64
-        movb  $X86_EXC_GP, EFRAME_entry_vector(%rsp)
-        jmp   handle_exception
-END(entry_GP)
-
-FUNC(entry_AC)
-        ENDBR64
-        movb  $X86_EXC_AC, EFRAME_entry_vector(%rsp)
-        jmp   handle_exception
-END(entry_AC)
-
 FUNC(entry_CP)
         ENDBR64
         movb  $X86_EXC_CP, EFRAME_entry_vector(%rsp)
@@ -1025,6 +1018,20 @@  FUNC(entry_DF)
         tailcall do_double_fault
 END(entry_DF)
 
+FUNC(entry_DB)
+        ENDBR64
+        pushq $0
+        movb  $X86_EXC_DB, EFRAME_entry_vector(%rsp)
+        jmp   handle_ist_exception
+END(entry_DB)
+
+FUNC(entry_MC)
+        ENDBR64
+        pushq $0
+        movb  $X86_EXC_MC, EFRAME_entry_vector(%rsp)
+        jmp   handle_ist_exception
+END(entry_MC)
+
 FUNC(entry_NMI)
         ENDBR64
         pushq $0
@@ -1161,13 +1168,6 @@  FUNC(handle_ist_exception)
 #endif
 END(handle_ist_exception)
 
-FUNC(entry_MC)
-        ENDBR64
-        pushq $0
-        movb  $X86_EXC_MC, EFRAME_entry_vector(%rsp)
-        jmp   handle_ist_exception
-END(entry_MC)
-
 /* No op trap handler.  Required for kexec crash path. */
 FUNC(trap_nop, 0)
         ENDBR64