x86/entry: replace two GET_CURRENT() uses

Now that we have %r14 set up using GET_STACK_END() in a number of
places, in two places we can eliminate the redundancy of GET_CURRENT()
also invoking that macro. In handle_ist_exception() actually go a step
farther and avoid using %rbx altogether when retrieving the processor
ID: Obtain the current vCPU pointer only in the PV32-specific code
actually needing it.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/x86_64/asm-offsets.c

@@ -118,6 +118,7 @@ void __dummy__(void)
 #endif
 
     OFFSET(CPUINFO_guest_cpu_user_regs, struct cpu_info, guest_cpu_user_regs);
+    OFFSET(CPUINFO_processor_id, struct cpu_info, processor_id);
     OFFSET(CPUINFO_verw_sel, struct cpu_info, verw_sel);
     OFFSET(CPUINFO_current_vcpu, struct cpu_info, current_vcpu);
     OFFSET(CPUINFO_per_cpu_offset, struct cpu_info, per_cpu_offset);

xen/arch/x86/x86_64/entry.S

@@ -749,7 +749,7 @@ FUNC(handle_exception, 0)
 .Lxcpt_cr3_okay:
 
 handle_exception_saved:
-        GET_CURRENT(bx)
+        mov   STACK_CPUINFO_FIELD(current_vcpu)(%r14), %rbx
         testb $X86_EFLAGS_IF>>8,UREGS_eflags+1(%rsp)
         jz    exception_with_ints_disabled
 
@@ -1130,9 +1130,8 @@ FUNC(handle_ist_exception)
 #ifdef CONFIG_PV
         testb $3,UREGS_cs(%rsp)
         jz    restore_all_xen
-        GET_CURRENT(bx)
         /* Send an IPI to ourselves to cover for the lack of event checking. */
-        movl  VCPU_processor(%rbx),%eax
+        mov   STACK_CPUINFO_FIELD(processor_id)(%r14), %eax
         shll  $IRQSTAT_shift,%eax
         leaq  irq_stat+IRQSTAT_softirq_pending(%rip),%rcx
         cmpl  $0,(%rcx,%rax,1)
@@ -1141,6 +1140,7 @@ FUNC(handle_ist_exception)
         call  send_IPI_self
 1:
 #ifdef CONFIG_PV32
+        mov   STACK_CPUINFO_FIELD(current_vcpu)(%r14), %rbx
         movq  VCPU_domain(%rbx),%rax
         cmpb  $0,DOMAIN_is_32bit_pv(%rax)
         je    restore_all_guest