x86/static-call: Remove early_boot_irqs_disabled check to fix Xen PVH dom0

__static_call_update_early() has a check for early_boot_irqs_disabled, but
is used before early_boot_irqs_disabled is set up in start_kernel().

Xen PV has always special cased early_boot_irqs_disabled, but Xen PVH does
not and falls over the BUG when booting as dom0.

It is very suspect that early_boot_irqs_disabled starts as 0, becomes 1 for
a time, then becomes 0 again, but as this needs backporting to fix a
breakage in a security fix, dropping the BUG_ON() is the far safer option.

Fixes: 0ef8047 ("x86/static-call: provide a way to do very early static-call updates")
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219620
Reported-by: Alex Zenla <[email protected]>
Suggested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Andrew Cooper <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Alex Zenla <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: andyhhp

arch/x86/kernel/static_call.c

@@ -175,7 +175,6 @@ EXPORT_SYMBOL_GPL(arch_static_call_transform);
 noinstr void __static_call_update_early(void *tramp, void *func)
 {
 	BUG_ON(system_state != SYSTEM_BOOTING);
-	BUG_ON(!early_boot_irqs_disabled);
 	BUG_ON(static_call_initialized);
 	__text_gen_insn(tramp, JMP32_INSN_OPCODE, tramp, func, JMP32_INSN_SIZE);
 	sync_core();