[tip: x86/urgent] x86/static-call: Remove early_boot_irqs_disabled check to fix Xen PVH dom0

[tip-bot2 for Andrew Cooper]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     5cc2db37124bb33914996d6fdbb2ddb3811f2945
Gitweb:        https://git.kernel.org/tip/5cc2db37124bb33914996d6fdbb2ddb3811f2945
Author:        Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate:    Sat, 21 Dec 2024 21:10:46 
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Thu, 02 Jan 2025 17:11:29 +01:00

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: 0ef8047b737d ("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 <alex@xxxxxxxxx>
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Alex Zenla <alex@xxxxxxxxx>
Link: https://lore.kernel.org/r/20241221211046.6475-1-andrew.cooper3@xxxxxxxxxx
---
 arch/x86/kernel/static_call.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
index 9eed0c1..9e51242 100644
--- a/arch/x86/kernel/static_call.c
+++ b/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();