x86/idt: Split idt_data setup out of set_intr_gate()

The code to setup idt_data is needed for early exception handling, but
set_intr_gate() can't be used that early because it has pv-ops in its
code path which don't work that early.

Split out the idt_data initialization part from set_intr_gate() so
that it can be used separately.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200907131613.12703-29-joro@8bytes.org

arch/x86/kernel/idt.c

@@ -205,18 +205,24 @@ idt_setup_from_table(gate_desc *idt, const struct idt_data *t, int size, bool sy
 	}
 }
 
+static void init_idt_data(struct idt_data *data, unsigned int n,
+			  const void *addr)
+{
+	BUG_ON(n > 0xFF);
+
+	memset(data, 0, sizeof(*data));
+	data->vector	= n;
+	data->addr	= addr;
+	data->segment	= __KERNEL_CS;
+	data->bits.type	= GATE_INTERRUPT;
+	data->bits.p	= 1;
+}
+
 static __init void set_intr_gate(unsigned int n, const void *addr)
 {
 	struct idt_data data;
 
-	BUG_ON(n > 0xFF);
+	init_idt_data(&data, n, addr);
-
-	memset(&data, 0, sizeof(data));
-	data.vector	= n;
-	data.addr	= addr;
-	data.segment	= __KERNEL_CS;
-	data.bits.type	= GATE_INTERRUPT;
-	data.bits.p	= 1;
 
 	idt_setup_from_table(idt_table, &data, 1, false);
 }