x86/xen: Use specific Xen pv interrupt entry for MCE

Xen PV guests don't use IST. For machine check interrupts, switch to the
same model as debug interrupts.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210120135555.32594-3-jgross@suse.com

arch/x86/include/asm/idtentry.h

@@ -585,6 +585,9 @@ DECLARE_IDTENTRY_MCE(X86_TRAP_MC,	exc_machine_check);
 #else
 DECLARE_IDTENTRY_RAW(X86_TRAP_MC,	exc_machine_check);
 #endif
+#ifdef CONFIG_XEN_PV
+DECLARE_IDTENTRY_RAW(X86_TRAP_MC,	xenpv_exc_machine_check);
+#endif
 #endif
 
 /* NMI */

arch/x86/xen/enlighten_pv.c

@@ -590,6 +590,20 @@ DEFINE_IDTENTRY_RAW(exc_xen_unknown_trap)
 	BUG();
 }
 
+#ifdef CONFIG_X86_MCE
+DEFINE_IDTENTRY_RAW(xenpv_exc_machine_check)
+{
+	/*
+	 * There's no IST on Xen PV, but we still need to dispatch
+	 * to the correct handler.
+	 */
+	if (user_mode(regs))
+		noist_exc_machine_check(regs);
+	else
+		exc_machine_check(regs);
+}
+#endif
+
 struct trap_array_entry {
 	void (*orig)(void);
 	void (*xen)(void);
@@ -610,7 +624,7 @@ static struct trap_array_entry trap_array[] = {
 	TRAP_ENTRY_REDIR(exc_debug,			true  ),
 	TRAP_ENTRY(exc_double_fault,			true  ),
 #ifdef CONFIG_X86_MCE
-	TRAP_ENTRY(exc_machine_check,			true  ),
+	TRAP_ENTRY_REDIR(exc_machine_check,		true  ),
 #endif
 	TRAP_ENTRY_REDIR(exc_nmi,			true  ),
 	TRAP_ENTRY(exc_int3,				false ),

arch/x86/xen/xen-asm.S

@@ -172,7 +172,7 @@ xen_pv_trap asm_exc_spurious_interrupt_bug
 xen_pv_trap asm_exc_coprocessor_error
 xen_pv_trap asm_exc_alignment_check
 #ifdef CONFIG_X86_MCE
-xen_pv_trap asm_exc_machine_check
+xen_pv_trap asm_xenpv_exc_machine_check
 #endif /* CONFIG_X86_MCE */
 xen_pv_trap asm_exc_simd_coprocessor_error
 #ifdef CONFIG_IA32_EMULATION