xen64: set up syscall and sysenter entrypoints for 64-bit

We set up entrypoints for syscall and sysenter.  sysenter is only used
for 32-bit compat processes, whereas syscall can be used in by both 32
and 64-bit processes.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 127 insertions, 2 deletions

diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index b147b495daef..4038cbfe3331 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -15,6 +15,8 @@
 
 #include <asm/asm-offsets.h>
 #include <asm/processor-flags.h>
+#include <asm/errno.h>
+#include <asm/segment.h>
 
 #include <xen/interface/xen.h>
 
@@ -138,9 +140,132 @@ ENTRY(xen_adjust_exception_frame)
         mov 8+8(%rsp),%r11
         ret $16
 
+hypercall_iret = hypercall_page + __HYPERVISOR_iret * 32
+/*
+        Xen64 iret frame:
+
+        ss
+        rsp
+        rflags
+        cs
+        rip             <-- standard iret frame
+
+        flags
+
+        rcx             }
+        r11             }<-- pushed by hypercall page
+rsp ->  rax             }
+ */
 ENTRY(xen_iret)
         pushq $0
-        jmp hypercall_page + __HYPERVISOR_iret * 32
+1:      jmp hypercall_iret
+ENDPATCH(xen_iret)
+RELOC(xen_iret, 1b+1)
 
+/*
+        sysexit is not used for 64-bit processes, so it's
+        only ever used to return to 32-bit compat userspace.
+ */
 ENTRY(xen_sysexit)
-        ud2a
+        pushq $__USER32_DS
+        pushq %rcx
+        pushq $X86_EFLAGS_IF
+        pushq $__USER32_CS
+        pushq %rdx
+
+        pushq $VGCF_in_syscall
+1:      jmp hypercall_iret
+ENDPATCH(xen_sysexit)
+RELOC(xen_sysexit, 1b+1)
+
+ENTRY(xen_sysret64)
+        /* We're already on the usermode stack at this point, but still
+           with the kernel gs, so we can easily switch back */
+        movq %rsp, %gs:pda_oldrsp
+        movq %gs:pda_kernelstack,%rsp
+
+        pushq $__USER_DS
+        pushq %gs:pda_oldrsp
+        pushq %r11
+        pushq $__USER_CS
+        pushq %rcx
+
+        pushq $VGCF_in_syscall
+1:      jmp hypercall_iret
+ENDPATCH(xen_sysret64)
+RELOC(xen_sysret64, 1b+1)
+
+ENTRY(xen_sysret32)
+        /* We're already on the usermode stack at this point, but still
+           with the kernel gs, so we can easily switch back */
+        movq %rsp, %gs:pda_oldrsp
+        movq %gs:pda_kernelstack, %rsp
+
+        pushq $__USER32_DS
+        pushq %gs:pda_oldrsp
+        pushq %r11
+        pushq $__USER32_CS
+        pushq %rcx
+
+        pushq $VGCF_in_syscall
+1:      jmp hypercall_iret
+ENDPATCH(xen_sysret32)
+RELOC(xen_sysret32, 1b+1)
+
+/*
+        Xen handles syscall callbacks much like ordinary exceptions,
+        which means we have:
+         - kernel gs
+         - kernel rsp
+         - an iret-like stack frame on the stack (including rcx and r11):
+                ss
+                rsp
+                rflags
+                cs
+                rip
+                r11
+        rsp->   rcx
+
+        In all the entrypoints, we undo all that to make it look
+        like a CPU-generated syscall/sysenter and jump to the normal
+        entrypoint.
+ */
+
+.macro undo_xen_syscall
+        mov 0*8(%rsp),%rcx
+        mov 1*8(%rsp),%r11
+        mov 5*8(%rsp),%rsp
+.endm
+
+/* Normal 64-bit system call target */
+ENTRY(xen_syscall_target)
+        undo_xen_syscall
+        jmp system_call_after_swapgs
+ENDPROC(xen_syscall_target)
+
+#ifdef CONFIG_IA32_EMULATION
+
+/* 32-bit compat syscall target */
+ENTRY(xen_syscall32_target)
+        undo_xen_syscall
+        jmp ia32_cstar_target
+ENDPROC(xen_syscall32_target)
+
+/* 32-bit compat sysenter target */
+ENTRY(xen_sysenter_target)
+        undo_xen_syscall
+        jmp ia32_sysenter_target
+ENDPROC(xen_sysenter_target)
+
+#else /* !CONFIG_IA32_EMULATION */
+
+ENTRY(xen_syscall32_target)
+ENTRY(xen_sysenter_target)
+        lea 16(%rsp), %rsp      /* strip %rcx,%r11 */
+        mov $-ENOSYS, %rax
+        pushq $VGCF_in_syscall
+        jmp hypercall_iret
+ENDPROC(xen_syscall32_target)
+ENDPROC(xen_sysenter_target)
+
+#endif  /* CONFIG_IA32_EMULATION */