x86/entry: Arrange for %r14 to be STACK_END across SPEC_CTRL_ENTRY_FROM_PV

Other SPEC_CTRL_* paths already use %r14 like this, and it will allow for
simplifications.

All instances of SPEC_CTRL_ENTRY_FROM_PV are followed by a GET_STACK_END()
invocation, so this change is only really logic and register shuffling.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit 22390697bf)

xen/arch/x86/x86_64/compat/entry.S

@@ -18,6 +18,8 @@ ENTRY(entry_int82)
         movl  $HYPERCALL_VECTOR, EFRAME_entry_vector(%rsp)
         SAVE_ALL compat=1 /* DPL1 gate, restricted to 32bit PV guests only. */
 
+        GET_STACK_END(14)
+
         SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
@@ -25,7 +27,7 @@ ENTRY(entry_int82)
 
         CR4_PV32_RESTORE
 
-        GET_CURRENT(bx)
+        movq STACK_CPUINFO_FIELD(current_vcpu)(%r14), %rbx
 
         mov   %rsp, %rdi
         call  do_entry_int82

xen/arch/x86/x86_64/entry.S

@@ -266,21 +266,22 @@ ENTRY(lstar_enter)
         movl  $TRAP_syscall, EFRAME_entry_vector(%rsp)
         SAVE_ALL
 
+        GET_STACK_END(14)
+
         SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
-        GET_STACK_END(bx)
-        mov   STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
+        mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
         test  %rcx, %rcx
         jz    .Llstar_cr3_okay
-        movb  $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%rbx)
+        movb  $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%r14)
         mov   %rcx, %cr3
         /* %r12 is still zero at this point. */
-        mov   %r12, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
+        mov   %r12, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
 .Llstar_cr3_okay:
         sti
 
-        movq  STACK_CPUINFO_FIELD(current_vcpu)(%rbx), %rbx
+        movq  STACK_CPUINFO_FIELD(current_vcpu)(%r14), %rbx
         testb $TF_kernel_mode,VCPU_thread_flags(%rbx)
         jz    switch_to_kernel
 
@@ -303,23 +304,24 @@ ENTRY(cstar_enter)
         movl  $TRAP_syscall, EFRAME_entry_vector(%rsp)
         SAVE_ALL
 
+        GET_STACK_END(14)
+
         SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
-        GET_STACK_END(bx)
-        mov   STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
+        mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
         test  %rcx, %rcx
         jz    .Lcstar_cr3_okay
-        movb  $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%rbx)
+        movb  $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%r14)
         mov   %rcx, %cr3
         /* %r12 is still zero at this point. */
-        mov   %r12, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
+        mov   %r12, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
 .Lcstar_cr3_okay:
         sti
 
         CR4_PV32_RESTORE
 
-        movq  STACK_CPUINFO_FIELD(current_vcpu)(%rbx), %rbx
+        movq  STACK_CPUINFO_FIELD(current_vcpu)(%r14), %rbx
 
 #ifdef CONFIG_PV32
         movq  VCPU_domain(%rbx), %rcx
@@ -344,23 +346,24 @@ GLOBAL(sysenter_eflags_saved)
         movl  $TRAP_syscall, EFRAME_entry_vector(%rsp)
         SAVE_ALL
 
+        GET_STACK_END(14)
+
         SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
-        GET_STACK_END(bx)
         /* PUSHF above has saved EFLAGS.IF clear (the caller had it set). */
         orl   $X86_EFLAGS_IF, UREGS_eflags(%rsp)
-        mov   STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
+        mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
         test  %rcx, %rcx
         jz    .Lsyse_cr3_okay
-        movb  $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%rbx)
+        movb  $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%r14)
         mov   %rcx, %cr3
         /* %r12 is still zero at this point. */
-        mov   %r12, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
+        mov   %r12, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
 .Lsyse_cr3_okay:
         sti
 
-        movq  STACK_CPUINFO_FIELD(current_vcpu)(%rbx), %rbx
+        movq  STACK_CPUINFO_FIELD(current_vcpu)(%r14), %rbx
         cmpb  $0,VCPU_sysenter_disables_events(%rbx)
         movq  VCPU_sysenter_addr(%rbx),%rax
         setne %cl
@@ -398,17 +401,18 @@ ENTRY(int80_direct_trap)
         movl  $0x80, EFRAME_entry_vector(%rsp)
         SAVE_ALL
 
+        GET_STACK_END(14)
+
         SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
-        GET_STACK_END(bx)
-        mov   STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
+        mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx
         test  %rcx, %rcx
         jz    .Lint80_cr3_okay
-        movb  $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%rbx)
+        movb  $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%r14)
         mov   %rcx, %cr3
         /* %r12 is still zero at this point. */
-        mov   %r12, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
+        mov   %r12, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
 .Lint80_cr3_okay:
         sti
 
@@ -418,7 +422,7 @@ UNLIKELY_START(ne, msi_check)
         call  check_for_unexpected_msi
 UNLIKELY_END(msi_check)
 
-        movq  STACK_CPUINFO_FIELD(current_vcpu)(%rbx), %rbx
+        movq  STACK_CPUINFO_FIELD(current_vcpu)(%r14), %rbx
 
         mov   VCPU_trap_ctxt(%rbx), %rsi
         mov   VCPU_domain(%rbx), %rax