exit/idt-shadow: allocate current_idt on the stack

We have 6 pages of stack space to use, no need to exhaust NonPagedPool.

exit.c

@@ -2084,17 +2084,11 @@ static inline void vcpu_sync_idt(struct vcpu *vcpu, struct gdtr *idt)
 	 * entries that we set, by simply just discarding them.
 	 */
 	size_t entries = min((size_t)idt->limit, (PAGE_SIZE - 1)) / sizeof(struct kidt_entry64);
-	struct kidt_entry64 *current_idt;
+	struct kidt_entry64 current_idt[256];
 	struct kidt_entry64 *shadow = (struct kidt_entry64 *)vcpu->idt.base;
 
-	current_idt = mm_alloc_page();
-	if (!current_idt)
-		return;
-
-	if (!ksm_read_virt(vcpu, idt->base, (u8 *)current_idt, idt->limit)) {
-		mm_free_pool(current_idt, PAGE_SIZE);
+	if (!ksm_read_virt(vcpu, idt->base, (u8 *)current_idt, idt->limit))
 		return vcpu_inject_pf(vcpu, idt->base, PGF_PRESENT);
-	}
 
 	KSM_DEBUG("Loading new IDT (new size: %d old size: %d)  Copying %d entries\n",
 		   idt->limit, vcpu->idt.limit, (int)entries);
@@ -2105,7 +2099,6 @@ static inline void vcpu_sync_idt(struct vcpu *vcpu, struct gdtr *idt)
 		if (!idte_present(&vcpu->shadow_idt[n]))
 			memcpy(&shadow[n], &current_idt[n], sizeof(*shadow));
 	vcpu_flush_idt(vcpu);
-	mm_free_page(current_idt);
 }
 
 static bool vcpu_handle_gdt_idt_access(struct vcpu *vcpu)