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[RFC,v2,3/7] x86/boot: Only jump into low trampoline code for real-mode boot

Message ID ec9a721d769910ff5e9d77caf036fb931a32ff1f.1556739209.git.dwmw2@infradead.org (mailing list archive)
State New, archived
Headers show
Series Clean up x86_64 boot code | expand

Commit Message

David Woodhouse May 1, 2019, 7:39 p.m. UTC 
From: David Woodhouse <dwmw@amazon.co.uk>

If the no-real-mode flag is set, don't go there at all. This is a prelude
to not even putting it there in the first place.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 xen/arch/x86/boot/head.S       | 10 ++++++++++
 xen/arch/x86/boot/trampoline.S |  4 ----
 2 files changed, 10 insertions(+), 4 deletions(-)
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Patch

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index db19ac6fd8..7c30de3671 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -734,7 +734,17 @@  trampoline_setup:
         /* Switch to low-memory stack which lives at the end of trampoline region. */
         mov     sym_fs(trampoline_phys),%edi
         lea     TRAMPOLINE_SPACE+TRAMPOLINE_STACK_SPACE(%edi),%esp
+        cmpb    $0, sym_fs(skip_realmode)
+        jz      1f
+        /* If no-real-mode, jump straight to trampoline_protmode_entry */
+        lea     trampoline_protmode_entry-trampoline_start(%edi),%eax
+        /* EBX == 0 indicates we are the BP (Boot Processor). */
+        xor     %ebx,%ebx
+        jmp     2f
+1:
+        /* Go via 16-bit code in trampoline_boot_cpu_entry */
         lea     trampoline_boot_cpu_entry-trampoline_start(%edi),%eax
+2:
         pushl   $BOOT_CS32
         push    %eax
 
diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 5588c7986a..df0ffd5013 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -187,9 +187,6 @@  start64:
 
         .code32
 trampoline_boot_cpu_entry:
-        cmpb    $0,bootsym_rel(skip_realmode,5)
-        jnz     .Lskip_realmode
-
         /* Load pseudo-real-mode segments. */
         mov     $BOOT_PSEUDORM_DS,%eax
         mov     %eax,%ds
@@ -269,7 +266,6 @@  trampoline_boot_cpu_entry:
         mov     %eax,%gs
         mov     %eax,%ss
 
-.Lskip_realmode:
         /* EBX == 0 indicates we are the BP (Boot Processor). */
         xor     %ebx,%ebx