[Xen-devel] [PATCH v4 7/8] x86: also NOP out xen_cr3 restores of XPTI

["Jan Beulich" <JBeulich@xxxxxxxx>]

... despite quite likely the gain being rather limited.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v4: Split off from earlier patch.

--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -583,7 +583,8 @@ ENTRY(common_interrupt)
         CR4_PV32_RESTORE
         movq %rsp,%rdi
         callq do_IRQ
-        mov   %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+        ALTERNATIVE __stringify(mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)), 
\
+                    "", X86_FEATURE_NO_XPTI
         jmp ret_from_intr
 
 ENTRY(page_fault)
@@ -665,7 +666,8 @@ handle_exception_saved:
         PERFC_INCR(exceptions, %rax, %rbx)
         mov   (%rdx, %rax, 8), %rdx
         INDIRECT_CALL %rdx
-        mov   %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+        ALTERNATIVE __stringify(mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)), 
\
+                    "", X86_FEATURE_NO_XPTI
         testb $3,UREGS_cs(%rsp)
         jz    restore_all_xen
         leaq  VCPU_trap_bounce(%rbx),%rdx
@@ -698,7 +700,8 @@ exception_with_ints_disabled:
         rep;  movsq                     # make room for ec/ev
 1:      movq  UREGS_error_code(%rsp),%rax # ec/ev
         movq  %rax,UREGS_kernel_sizeof(%rsp)
-        mov   %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+        ALTERNATIVE __stringify(mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)), 
\
+                    "", X86_FEATURE_NO_XPTI
         jmp   restore_all_xen           # return to fixup code
 
 /* No special register assumptions. */
@@ -849,7 +852,8 @@ handle_ist_exception:
         leaq  exception_table(%rip),%rdx
         mov   (%rdx, %rax, 8), %rdx
         INDIRECT_CALL %rdx
-        mov   %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+        ALTERNATIVE __stringify(mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)), 
\
+                    "", X86_FEATURE_NO_XPTI
         cmpb  $TRAP_nmi,UREGS_entry_vector(%rsp)
         jne   ret_from_intr
 




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