[librm] Add support for installing a startup IPI handler

Application processors are started via INIT and SIPI interprocessor
interrupts: the INIT places the processor into a "wait for SIPI"
state, and the SIPI then starts the processor in real mode at a
page-aligned address derived from the SIPI vector number.

Add support for installing a real-mode SIPI handler that will switch
the CPU into protected mode with flat physical addressing, load
initial register contents, and then jump to the address of a
protected-mode SIPI handler.  No stack pointer is set up, to avoid the
need to allocate stack space for each available processor.

We use 32-bit physical addressing in order to minimise the changes
required for a 64-bit build.  The existing long mode transition code
relies on the existence of the stack, so we cannot easily switch the
application processor into long mode.  We could use 32-bit virtual
addressing, but this runtime environment does not currently exist
outside of librm.S itself in a 64-bit build, and using it would
complicate the implementation of the protected-mode SIPI handler.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/src/arch/x86/transitions/librm_mgmt.c b/src/arch/x86/transitions/librm_mgmt.c
index da221e8b..b3820589 100644
--- a/src/arch/x86/transitions/librm_mgmt.c
+++ b/src/arch/x86/transitions/librm_mgmt.c
@@ -45,6 +45,9 @@ struct idtr64 idtr64 = {
 	.limit = ( sizeof ( idt64 ) - 1 ),
 };
 
+/** Startup IPI register state */
+struct i386_regs sipi_regs;
+
 /** Length of stack dump */
 #define STACK_DUMP_LEN 128
 
@@ -402,6 +405,29 @@ __asmcall void check_fxsr ( struct i386_all_regs *regs ) {
 	       ( ( regs->flags & CF ) ? " not" : "" ) );
 }
 
+/**
+ * Set up startup IPI handler
+ *
+ * @v vector		Startup IPI vector
+ * @v handler		Protected-mode startup IPI handler physical address
+ * @v regs		Initial register state
+ */
+void setup_sipi ( unsigned int vector, uint32_t handler,
+		  struct i386_regs *regs ) {
+
+	/* Record protected-mode handler */
+	sipi_handler = handler;
+
+	/* Update copy of rm_ds */
+	sipi_ds = rm_ds;
+
+	/* Save register state */
+	memcpy ( &sipi_regs, regs, sizeof ( sipi_regs ) );
+
+	/* Copy real-mode handler */
+	copy_to_real ( ( vector << 8 ), 0, sipi, ( ( size_t ) sipi_len ) );
+}
+
 PROVIDE_UACCESS_INLINE ( librm, phys_to_user );
 PROVIDE_UACCESS_INLINE ( librm, user_to_phys );
 PROVIDE_UACCESS_INLINE ( librm, virt_to_user );