x86/entry: Use POP_GPRS and remove RESTORE_ALL

POP_GPRS is shorter than RESTORE_ALL in terms of emitted code.

By separating the popping of entry_vector/error_code off the stack,
SPEC_CTRL_COND_VERW doesn't need custom displacements.

Get rid of the compat=1 special case for PV32.  It's not obviously a win, and
PV32 is getting increasingly rare these days.

No functional change.

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

xen/arch/x86/include/asm/asm_defns.h

@@ -264,54 +264,6 @@ static always_inline void stac(void)
         xor   %r15d, %r15d
 .endm
 
-#define LOAD_ONE_REG(reg, compat) \
-.if !(compat); \
-        movq  UREGS_r##reg(%rsp),%r##reg; \
-.else; \
-        movl  UREGS_r##reg(%rsp),%e##reg; \
-.endif
-
-/*
- * Restore all previously saved registers.
- *
- * @adj: extra stack pointer adjustment to be folded into the adjustment done
- *       anyway at the end of the macro
- * @compat: R8-R15 don't need reloading, but they are clobbered for added
- *          safety against information leaks.
- */
-.macro RESTORE_ALL adj=0, compat=0
-.if !\compat
-        movq  UREGS_r15(%rsp), %r15
-        movq  UREGS_r14(%rsp), %r14
-        movq  UREGS_r13(%rsp), %r13
-        movq  UREGS_r12(%rsp), %r12
-.else
-        xor %r15d, %r15d
-        xor %r14d, %r14d
-        xor %r13d, %r13d
-        xor %r12d, %r12d
-.endif
-        LOAD_ONE_REG(bp, \compat)
-        LOAD_ONE_REG(bx, \compat)
-.if !\compat
-        movq  UREGS_r11(%rsp),%r11
-        movq  UREGS_r10(%rsp),%r10
-        movq  UREGS_r9(%rsp),%r9
-        movq  UREGS_r8(%rsp),%r8
-.else
-        xor %r11d, %r11d
-        xor %r10d, %r10d
-        xor %r9d, %r9d
-        xor %r8d, %r8d
-.endif
-        LOAD_ONE_REG(ax, \compat)
-        LOAD_ONE_REG(cx, \compat)
-        LOAD_ONE_REG(dx, \compat)
-        LOAD_ONE_REG(si, \compat)
-        LOAD_ONE_REG(di, \compat)
-        subq  $-(UREGS_error_code-UREGS_r15+\adj), %rsp
-.endm
-
 /*
  * Push and clear GPRs
  */
@@ -369,7 +321,7 @@ static always_inline void stac(void)
         pop   %r9
         pop   %r8
  .if \skip_rax
-        pop   %rcx
+        pop   %rcx /* Any register yet to restore. */
  .else
         pop   %rax
  .endif

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

@@ -160,12 +160,11 @@ FUNC(compat_restore_all_guest)
         /* WARNING! `ret`, `call *`, `jmp *` not safe beyond this point. */
         SPEC_CTRL_EXIT_TO_PV    /* Req: a=spec_ctrl %rsp=regs/cpuinfo, Clob: cd */
 
-        RESTORE_ALL adj=8, compat=1
+        POP_GPRS
 
-        /* Account for ev/ec having already been popped off the stack. */
-        SPEC_CTRL_COND_VERW \
-            scf=STK_REL(CPUINFO_scf,      CPUINFO_rip), \
-            sel=STK_REL(CPUINFO_verw_sel, CPUINFO_rip)
+        SPEC_CTRL_COND_VERW     /* Req: %rsp=eframe                    Clob: efl */
+
+        add     $8, %rsp        /* Pop ev/ec off the stack */
 
         jmp     iret_to_guest
 END(compat_restore_all_guest)

xen/arch/x86/x86_64/entry.S

@@ -226,7 +226,8 @@ FUNC_LOCAL(restore_all_guest)
         /* WARNING! `ret`, `call *`, `jmp *` not safe beyond this point. */
         SPEC_CTRL_EXIT_TO_PV    /* Req: a=spec_ctrl %rsp=regs/cpuinfo, Clob: cd */
 
-        RESTORE_ALL
+        POP_GPRS
+
         BUILD_BUG_ON(TRAP_syscall & 0xff)
         testb $TRAP_syscall >> 8, EFRAME_entry_vector + 1(%rsp)
         jz    iret_exit_to_guest
@@ -753,20 +754,17 @@ UNLIKELY_END(exit_cr3)
         /* WARNING! `ret`, `call *`, `jmp *` not safe beyond this point. */
         SPEC_CTRL_EXIT_TO_XEN /* Req: %r12=ist_exit %r14=end %rsp=regs, Clob: abcd */
 
-        RESTORE_ALL adj=8
+        POP_GPRS
 
         /*
          * When the CPU pushed this exception frame, it zero-extended eflags.
          * For an IST exit, SPEC_CTRL_EXIT_TO_XEN stashed shadow copies of
          * scf and ver_sel above eflags, as we can't use any GPRs,
          * and we're at a random place on the stack, not in a CPUFINFO block.
-         *
-         * Account for ev/ec having already been popped off the stack.
          */
-        SPEC_CTRL_COND_VERW \
-            scf=STK_REL(EFRAME_shadow_scf, EFRAME_rip), \
-            sel=STK_REL(EFRAME_shadow_sel, EFRAME_rip)
+        SPEC_CTRL_COND_VERW     /* Req: %rsp=eframe                    Clob: efl */
 
+        add     $8, %rsp        /* Pop ev/ec off the stack */
         iretq
 END(restore_all_xen)