1 files changed, 17 insertions, 1 deletions
diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
index 9b93567d663a..6debb816e83d 100644
--- a/arch/x86/boot/compressed/idt_64.c
+++ b/arch/x86/boot/compressed/idt_64.c
@@ -39,7 +39,23 @@ void load_stage1_idt(void)
 	load_boot_idt(&boot_idt_desc);
 }
 
-/* Setup IDT after kernel jumping to  .Lrelocated */
+/*
+ * Setup IDT after kernel jumping to  .Lrelocated.
+ *
+ * initialize_identity_maps() needs a #PF handler to be setup
+ * in order to be able to fault-in identity mapping ranges; see
+ * do_boot_page_fault().
+ *
+ * This #PF handler setup needs to happen in load_stage2_idt() where the
+ * IDT is loaded and there the #VC IDT entry gets setup too.
+ *
+ * In order to be able to handle #VCs, one needs a GHCB which
+ * gets setup with an already set up pagetable, which is done in
+ * initialize_identity_maps(). And there's the catch 22: the boot #VC
+ * handler do_boot_stage2_vc() needs to call early_setup_ghcb() itself
+ * (and, especially set_page_decrypted()) because the SEV-ES setup code
+ * cannot initialize a GHCB as there's no #PF handler yet...
+ */
 void load_stage2_idt(void)
 {
 	boot_idt_desc.address = (unsigned long)boot_idt;