[xen staging-4.16] x86/spec_ctrl: Hold SCF in %ebx across SPEC_CTRL_ENTRY_{PV,INTR}

[patchbot@xxxxxxx]

commit 6107fa01870e33ab59969f5f21f959352a3670d5
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Mar 22 12:08:02 2024 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Apr 9 17:10:28 2024 +0100

    x86/spec_ctrl: Hold SCF in %ebx across SPEC_CTRL_ENTRY_{PV,INTR}
    
    ... as we do in the exit paths too.  This will allow simplification to the
    sub-blocks.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 9607aeb6602b8ed9962404de3f5f90170ffddb66)
---
 xen/arch/x86/x86_64/compat/entry.S  |  2 +-
 xen/arch/x86/x86_64/entry.S         | 12 ++++++------
 xen/include/asm-x86/spec_ctrl_asm.h | 10 +++++++---
 3 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/x86_64/compat/entry.S 
b/xen/arch/x86/x86_64/compat/entry.S
index a32b95f7c3..ff462a92e0 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -20,7 +20,7 @@ ENTRY(entry_int82)
 
         GET_STACK_END(14)
 
-        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
+        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %r14=end, %rdx=0, 
Clob: abcd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         sti
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index c52229d032..09f143354e 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -268,7 +268,7 @@ ENTRY(lstar_enter)
 
         GET_STACK_END(14)
 
-        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
+        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %r14=end, %rdx=0, 
Clob: abcd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
@@ -306,7 +306,7 @@ ENTRY(cstar_enter)
 
         GET_STACK_END(14)
 
-        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
+        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %r14=end, %rdx=0, 
Clob: abcd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
@@ -348,7 +348,7 @@ GLOBAL(sysenter_eflags_saved)
 
         GET_STACK_END(14)
 
-        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
+        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %r14=end, %rdx=0, 
Clob: abcd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         /* PUSHF above has saved EFLAGS.IF clear (the caller had it set). */
@@ -403,7 +403,7 @@ ENTRY(int80_direct_trap)
 
         GET_STACK_END(14)
 
-        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
+        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %r14=end, %rdx=0, 
Clob: abcd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
@@ -704,7 +704,7 @@ ENTRY(common_interrupt)
 
         GET_STACK_END(14)
 
-        SPEC_CTRL_ENTRY_FROM_INTR /* Req: %rsp=regs, %r14=end, %rdx=0, Clob: 
acd */
+        SPEC_CTRL_ENTRY_FROM_INTR /* Req: %rsp=regs, %r14=end, %rdx=0, Clob: 
abcd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
@@ -738,7 +738,7 @@ GLOBAL(handle_exception)
 
         GET_STACK_END(14)
 
-        SPEC_CTRL_ENTRY_FROM_INTR /* Req: %rsp=regs, %r14=end, %rdx=0, Clob: 
acd */
+        SPEC_CTRL_ENTRY_FROM_INTR /* Req: %rsp=regs, %r14=end, %rdx=0, Clob: 
abcd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
diff --git a/xen/include/asm-x86/spec_ctrl_asm.h 
b/xen/include/asm-x86/spec_ctrl_asm.h
index d536a79f28..de6a6e4ff1 100644
--- a/xen/include/asm-x86/spec_ctrl_asm.h
+++ b/xen/include/asm-x86/spec_ctrl_asm.h
@@ -268,9 +268,11 @@
  */
 .macro SPEC_CTRL_ENTRY_FROM_PV
 /*
- * Requires %rsp=regs/cpuinfo, %rdx=0
- * Clobbers %rax, %rcx, %rdx
+ * Requires %rsp=regs/cpuinfo, %r14=stack_end, %rdx=0
+ * Clobbers %rax, %rbx, %rcx, %rdx
  */
+    movzbl STACK_CPUINFO_FIELD(scf)(%r14), %ebx
+
     ALTERNATIVE "", __stringify(DO_SPEC_CTRL_COND_IBPB maybexen=0),     \
         X86_FEATURE_IBPB_ENTRY_PV
 
@@ -294,8 +296,10 @@
 .macro SPEC_CTRL_ENTRY_FROM_INTR
 /*
  * Requires %rsp=regs, %r14=stack_end, %rdx=0
- * Clobbers %rax, %rcx, %rdx
+ * Clobbers %rax, %rbx, %rcx, %rdx
  */
+    movzbl STACK_CPUINFO_FIELD(scf)(%r14), %ebx
+
     testb $3, UREGS_cs(%rsp)
     jz .L\@_skip
 
--
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