x86/entry: Switch XEN/PV hypercall entry to IDTENTRY

Convert the XEN/PV hypercall to IDTENTRY:

  - Emit the ASM stub with DECLARE_IDTENTRY
  - Remove the ASM idtentry in 64-bit
  - Remove the open coded ASM entry code in 32-bit
  - Remove the old prototypes

The handler stubs need to stay in ASM code as they need corner case handling
and adjustment of the stack pointer.

Provide a new C function which invokes the entry/exit handling and calls
into the XEN handler on the interrupt stack if required.

The exit code is slightly different from the regular idtentry_exit() on
non-preemptible kernels. If the hypercall is preemptible and need_resched()
is set then XEN provides a preempt hypercall scheduling function.

Move this functionality into the entry code so it can use the existing
idtentry functionality.

[ mingo: Build fixes. ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Juergen Gross <jgross@suse.com>
Tested-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20200521202118.055270078@linutronix.de

1 files changed, 34 insertions, 0 deletions

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index b05688973b92..b2a5fe02dcf0 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -165,6 +165,21 @@ __visible noinstr void func(struct pt_regs *regs)
 #define DEFINE_IDTENTRY_RAW_ERRORCODE(func)				\
 __visible noinstr void func(struct pt_regs *regs, unsigned long error_code)
 
+/**
+ * DECLARE_IDTENTRY_XENCB - Declare functions for XEN HV callback entry point
+ * @vector:	Vector number (ignored for C)
+ * @func:	Function name of the entry point
+ *
+ * Declares three functions:
+ * - The ASM entry point: asm_##func
+ * - The XEN PV trap entry point: xen_##func (maybe unused)
+ * - The C handler called from the ASM entry point
+ *
+ * Maps to DECLARE_IDTENTRY(). Distinct entry point to handle the 32/64-bit
+ * difference
+ */
+#define DECLARE_IDTENTRY_XENCB(vector, func)				\
+	DECLARE_IDTENTRY(vector, func)
 
 #ifdef CONFIG_X86_64
 /**
@@ -307,6 +322,9 @@ __visible noinstr void func(struct pt_regs *regs,			\
 # define DECLARE_IDTENTRY_DF(vector, func)				\
 	idtentry_df vector asm_##func func
 
+# define DECLARE_IDTENTRY_XENCB(vector, func)				\
+	DECLARE_IDTENTRY(vector, func)
+
 #else
 # define DECLARE_IDTENTRY_MCE(vector, func)				\
 	DECLARE_IDTENTRY(vector, func)
@@ -317,6 +335,9 @@ __visible noinstr void func(struct pt_regs *regs,			\
 /* No ASM emitted for DF as this goes through a C shim */
 # define DECLARE_IDTENTRY_DF(vector, func)
 
+/* No ASM emitted for XEN hypervisor callback */
+# define DECLARE_IDTENTRY_XENCB(vector, func)
+
 #endif
 
 /* No ASM code emitted for NMI */
@@ -337,6 +358,13 @@ __visible noinstr void func(struct pt_regs *regs,			\
  * This avoids duplicate defines and ensures that everything is consistent.
  */
 
+/*
+ * Dummy trap number so the low level ASM macro vector number checks do not
+ * match which results in emitting plain IDTENTRY stubs without bells and
+ * whistels.
+ */
+#define X86_TRAP_OTHER		0xFFFF
+
 /* Simple exception entry points. No hardware error code */
 DECLARE_IDTENTRY(X86_TRAP_DE,		exc_divide_error);
 DECLARE_IDTENTRY(X86_TRAP_OF,		exc_overflow);
@@ -376,4 +404,10 @@ DECLARE_IDTENTRY_XEN(X86_TRAP_DB,	debug);
 /* #DF */
 DECLARE_IDTENTRY_DF(X86_TRAP_DF,	exc_double_fault);
 
+#ifdef CONFIG_XEN_PV
+DECLARE_IDTENTRY_XENCB(X86_TRAP_OTHER,	exc_xen_hypervisor_callback);
+#endif
+
+#undef X86_TRAP_OTHER
+
 #endif