VMX: streamline entry.S code

- move stuff easily/better done in C into C code
- re-arrange code paths so that no redundant GET_CURRENT() would remain
  on the fast paths
- move long latency operations earlier
- slightly defer disabling interrupts on the VM entry path
- use ENTRY() instead of open coding it

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

xen/arch/x86/hvm/vmx/entry.S

@@ -28,109 +28,66 @@
 
 #define VMRESUME     .byte 0x0f,0x01,0xc3
 #define VMLAUNCH     .byte 0x0f,0x01,0xc2
-#define VMREAD(off)  .byte 0x0f,0x78,0x47,((off)-UREGS_rip)
-#define VMWRITE(off) .byte 0x0f,0x79,0x47,((off)-UREGS_rip)
 
-/* VMCS field encodings */
-#define GUEST_RSP    0x681c
-#define GUEST_RIP    0x681e
-#define GUEST_RFLAGS 0x6820
-
-        ALIGN
-.globl vmx_asm_vmexit_handler
-vmx_asm_vmexit_handler:
+ENTRY(vmx_asm_vmexit_handler)
         push %rdi
         push %rsi
         push %rdx
         push %rcx
         push %rax
+        mov  %cr2,%rax
         push %r8
         push %r9
         push %r10
         push %r11
         push %rbx
+        GET_CURRENT(%rbx)
         push %rbp
         push %r12
         push %r13
         push %r14
         push %r15
 
-        GET_CURRENT(%rbx)
-
         movb $1,VCPU_vmx_launched(%rbx)
-
-        lea  UREGS_rip(%rsp),%rdi
-        mov  $GUEST_RIP,%eax
-        /*VMREAD(UREGS_rip)*/
-        .byte 0x0f,0x78,0x07  /* vmread %rax,(%rdi) */
-        mov  $GUEST_RSP,%eax
-        VMREAD(UREGS_rsp)
-        mov  $GUEST_RFLAGS,%eax
-        VMREAD(UREGS_eflags)
-
-        mov  %cr2,%rax
         mov  %rax,VCPU_hvm_guest_cr2(%rbx)
 
-#ifndef NDEBUG
-        mov  $0xbeef,%ax
-        mov  %ax,UREGS_error_code(%rsp)
-        mov  %ax,UREGS_entry_vector(%rsp)
-        mov  %ax,UREGS_saved_upcall_mask(%rsp)
-        mov  %ax,UREGS_cs(%rsp)
-        mov  %ax,UREGS_ds(%rsp)
-        mov  %ax,UREGS_es(%rsp)
-        mov  %ax,UREGS_fs(%rsp)
-        mov  %ax,UREGS_gs(%rsp)
-        mov  %ax,UREGS_ss(%rsp)
-#endif
-
         mov  %rsp,%rdi
         call vmx_vmexit_handler
 
-.globl vmx_asm_do_vmentry
-vmx_asm_do_vmentry:
+.Lvmx_do_vmentry:
         call vmx_intr_assist
         call nvmx_switch_guest
         ASSERT_NOT_IN_ATOMIC
 
-        GET_CURRENT(%rbx)
-        cli
-
         mov  VCPU_processor(%rbx),%eax
-        shl  $IRQSTAT_shift,%eax
         lea  irq_stat+IRQSTAT_softirq_pending(%rip),%rdx
-        cmpl $0,(%rdx,%rax,1)
+        xor  %ecx,%ecx
+        shl  $IRQSTAT_shift,%eax
+        cli
+        cmp  %ecx,(%rdx,%rax,1)
         jnz  .Lvmx_process_softirqs
 
-        testb $0xff,VCPU_vmx_emulate(%rbx)
-        jnz .Lvmx_goto_emulator
-        testb $0xff,VCPU_vmx_realmode(%rbx)
-UNLIKELY_START(nz, realmode)
-        cmpw $0,VCPU_vm86_seg_mask(%rbx)
+        cmp  %cl,VCPU_vmx_emulate(%rbx)
+        jne .Lvmx_goto_emulator
+        cmp  %cl,VCPU_vmx_realmode(%rbx)
+UNLIKELY_START(ne, realmode)
+        cmp  %cx,VCPU_vm86_seg_mask(%rbx)
         jnz .Lvmx_goto_emulator
         mov  %rsp,%rdi
         call vmx_enter_realmode
 UNLIKELY_END(realmode)
 
+        mov  %rsp,%rdi
         call vmx_vmenter_helper
         mov  VCPU_hvm_guest_cr2(%rbx),%rax
-        mov  %rax,%cr2
 
-        lea  UREGS_rip(%rsp),%rdi
-        mov  $GUEST_RIP,%eax
-        /*VMWRITE(UREGS_rip)*/
-        .byte 0x0f,0x79,0x07  /* vmwrite (%rdi),%rax */
-        mov  $GUEST_RSP,%eax
-        VMWRITE(UREGS_rsp)
-        mov  $GUEST_RFLAGS,%eax
-        VMWRITE(UREGS_eflags)
-
-        cmpb $0,VCPU_vmx_launched(%rbx)
         pop  %r15
         pop  %r14
         pop  %r13
         pop  %r12
         pop  %rbp
+        mov  %rax,%cr2
+        cmpb $0,VCPU_vmx_launched(%rbx)
         pop  %rbx
         pop  %r11
         pop  %r10
@@ -155,13 +112,17 @@ UNLIKELY_END(realmode)
         call vm_launch_fail
         ud2
 
+ENTRY(vmx_asm_do_vmentry)
+        GET_CURRENT(%rbx)
+        jmp  .Lvmx_do_vmentry
+
 .Lvmx_goto_emulator:
         sti
         mov  %rsp,%rdi
         call vmx_realmode
-        jmp  vmx_asm_do_vmentry
+        jmp  .Lvmx_do_vmentry
 
 .Lvmx_process_softirqs:
         sti
         call do_softirq
-        jmp  vmx_asm_do_vmentry
+        jmp  .Lvmx_do_vmentry

xen/arch/x86/hvm/vmx/vmx.c

@@ -2377,6 +2377,12 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
     unsigned long exit_qualification, inst_len = 0;
     struct vcpu *v = current;
 
+    regs->rip    = __vmread(GUEST_RIP);
+    regs->rsp    = __vmread(GUEST_RSP);
+    regs->rflags = __vmread(GUEST_RFLAGS);
+
+    hvm_invalidate_regs_fields(regs);
+
     if ( paging_mode_hap(v->domain) && hvm_paging_enabled(v) )
         v->arch.hvm_vcpu.guest_cr[3] = v->arch.hvm_vcpu.hw_cr[3] =
             __vmread(GUEST_CR3);
@@ -2870,7 +2876,7 @@ out:
         nvmx_idtv_handling();
 }
 
-void vmx_vmenter_helper(void)
+void vmx_vmenter_helper(const struct cpu_user_regs *regs)
 {
     struct vcpu *curr = current;
     u32 new_asid, old_asid;
@@ -2912,6 +2918,10 @@ void vmx_vmenter_helper(void)
 
  out:
     HVMTRACE_ND(VMENTRY, 0, 1/*cycles*/, 0, 0, 0, 0, 0, 0, 0);
+
+    __vmwrite(GUEST_RIP,    regs->rip);
+    __vmwrite(GUEST_RSP,    regs->rsp);
+    __vmwrite(GUEST_RFLAGS, regs->rflags);
 }
 
 /*

xen/include/asm-x86/hvm/hvm.h

@@ -439,6 +439,21 @@ static inline void hvm_set_info_guest(struct vcpu *v)
 
 int hvm_debug_op(struct vcpu *v, int32_t op);
 
+static inline void hvm_invalidate_regs_fields(struct cpu_user_regs *regs)
+{
+#ifndef NDEBUG
+    regs->error_code = 0xbeef;
+    regs->entry_vector = 0xbeef;
+    regs->saved_upcall_mask = 0xbf;
+    regs->cs = 0xbeef;
+    regs->ss = 0xbeef;
+    regs->ds = 0xbeef;
+    regs->es = 0xbeef;
+    regs->fs = 0xbeef;
+    regs->gs = 0xbeef;
+#endif
+}
+
 int hvm_hap_nested_page_fault(paddr_t gpa,
                               bool_t gla_valid, unsigned long gla,
                               bool_t access_r,