[PATCH v3 1/4] x86/HVM: don't (almost) open-code POP_GPRS

[Jan Beulich <jbeulich@xxxxxxxx>]

It can be used as-is for VMX. For SVM the special treatment of %rax needs
accounting for.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
This is the minimum required as a prereq to the next patch (to avoid the
need for custom adjustments in the two places). We could go further and
switch to using PUSH_AND_CLEAR_GPRS at the same time.
---
v3: New.

--- a/xen/arch/x86/hvm/svm/entry.S
+++ b/xen/arch/x86/hvm/svm/entry.S
@@ -82,22 +82,8 @@ __UNLIKELY_END(nsvm_hap)
          */
         sti
 
-        pop  %r15
-        pop  %r14
-        pop  %r13
-        pop  %r12
-        pop  %rbp
         mov  VCPU_svm_vmcb_pa(%rbx),%rax
-        pop  %rbx
-        pop  %r11
-        pop  %r10
-        pop  %r9
-        pop  %r8
-        pop  %rcx /* Skip %rax: restored by VMRUN. */
-        pop  %rcx
-        pop  %rdx
-        pop  %rsi
-        pop  %rdi
+        POP_GPRS skip_rax=1 /* %rax restored by VMRUN. */
 
         SPEC_CTRL_COND_VERW     /* Req: %rsp=eframe                    Clob: 
efl */
 
--- a/xen/arch/x86/hvm/vmx/entry.S
+++ b/xen/arch/x86/hvm/vmx/entry.S
@@ -139,21 +139,7 @@ UNLIKELY_END(realmode)
         and  $SCF_verw, %eax
         or   %eax, %ecx
 
-        pop  %r15
-        pop  %r14
-        pop  %r13
-        pop  %r12
-        pop  %rbp
-        pop  %rbx
-        pop  %r11
-        pop  %r10
-        pop  %r9
-        pop  %r8
-        pop  %rax
-        pop  %rcx
-        pop  %rdx
-        pop  %rsi
-        pop  %rdi
+        POP_GPRS /* Preserves flags. */
 
         jpe  .L_skip_verw
         /* VERW clobbers ZF, but preserves all others, including SF. */
--- a/xen/arch/x86/include/asm/asm_defns.h
+++ b/xen/arch/x86/include/asm/asm_defns.h
@@ -357,7 +357,7 @@ static always_inline void stac(void)
 /*
  * POP GPRs from a UREGS_* frame on the stack.  Does not modify flags.
  */
-.macro POP_GPRS
+.macro POP_GPRS skip_rax=0
         pop   %r15
         pop   %r14
         pop   %r13
@@ -368,7 +368,11 @@ static always_inline void stac(void)
         pop   %r10
         pop   %r9
         pop   %r8
+ .if \skip_rax
+        pop   %rcx
+ .else
         pop   %rax
+ .endif
         pop   %rcx
         pop   %rdx
         pop   %rsi