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[PATCH] x86/entry: re-order exception entry points


  • To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 6 Mar 2024 14:57:06 +0100
  • Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Wed, 06 Mar 2024 13:57:16 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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 <jbeulich@xxxxxxxx>
---
Arguably we could move all these entry points ahead of handle_exception,
accepting that the first few will continue to use Disp32 JMPs.

--- 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



 


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