Re: [PATCH v1] efi/runtime-wrappers: Avoid crashing on early PRM code invocations

["Rafael J. Wysocki" <rafael@kernel.org>]

On Friday, May 15, 2026 7:29:03 PM CEST Ard Biesheuvel wrote:
> Hi Rafael,
> 
> On Fri, 15 May 2026, at 19:10, Rafael J. Wysocki wrote:
> > From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> >
> > There is a dependency between EFI and ACPI PRM that the latter cannot
> > run until the former is ready and PRM can be invoked from AML early
> > through acpi_platformrt_space_handler().  If that happens before
> > initializing efi_rts_wq, it leads to a NULL pointer dereference.
> >
> > Avoid that by adding an efi_rts_wq check against NULL to
> > efi_call_acpi_prm_handler().
> >
> > Fixes: 5894cf571e14 ("acpi/prmt: Use EFI runtime sandbox to invoke PRM 
> > handlers")
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Cc: 6.6+ <stable@vger.kernel.org> # 6.6+
> > ---
> >
> > An alternative would be to somehow ensure that efisubsys_init() will always
> > run before acpi_init(), but moving any of them to another initcall level is
> > not an option AFAICS.
> >
> 
> Given that they both run as subsys_initcall() currently, changing acpi_init()
> to subsys_initcall_sync() is probably fine (famous last words :-))

Well, not quite because there is stuff depending on ACPI in that initcall level
(MWI and CXL, probably among other things).

> But if the PRM code can deal with EFI_NOT_READY than this is also fine,
> modulo the comment below.

It can, but that is not ideal because if EFI_NOT_READY is returned, so AML will
be aborted and that may be something like a GPE handler method, so it would be
better to ensure the working order.

Something like the patch below can be done.  It works AFAICS, but the initcall
error handling is a bit awkward (it is for debug though, so not a big deal I
guess).  If this is acceptable, I can send it as a v2.

---
 drivers/acpi/bus.c         |    8 +++++++-
 drivers/firmware/efi/efi.c |   16 +++++++++++++++-
 include/acpi/acpi_bus.h    |    4 ++++
 3 files changed, 26 insertions(+), 2 deletions(-)

--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -1490,7 +1490,7 @@ EXPORT_SYMBOL_GPL(acpi_kobj);
 
 void __weak __init acpi_arch_init(void) { }
 
-static int __init acpi_init(void)
+int __init acpi_init(void)
 {
 	int result;
 
@@ -1531,4 +1531,10 @@ static int __init acpi_init(void)
 	return 0;
 }
 
+/*
+ * If EFI is enabled, it needs to initialize before ACPI due to a PRM
+ * dependency, so in that case acpi_init() will be called from there.
+ */
+#ifndef CONFIG_EFI
 subsys_initcall(acpi_init);
+#endif
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -500,7 +500,21 @@ err_destroy_wq:
 	return error;
 }
 
-subsys_initcall(efisubsys_init);
+static int __init efisubsys_and_acpi_init(void)
+{
+	int efi_ret, acpi_ret;
+
+	efi_ret = efisubsys_init();
+
+	/* Initialize ACPI after EFI to satisfy a PRM dependency. */
+	acpi_ret = acpi_init();
+
+	if (efi_ret)
+		return efi_ret;
+
+	return acpi_ret;
+}
+subsys_initcall(efisubsys_and_acpi_init);
 
 void __init efi_find_mirror(void)
 {
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -92,6 +92,8 @@ bool acpi_reduced_hardware(void);
 
 #ifdef CONFIG_ACPI
 
+int __init acpi_init(void);
+
 struct proc_dir_entry;
 
 #define ACPI_BUS_FILE_ROOT	"acpi"
@@ -994,6 +996,8 @@ int acpi_scan_add_dep(acpi_handle handle
 u32 arch_acpi_add_auto_dep(acpi_handle handle);
 #else	/* CONFIG_ACPI */
 
+static inline int acpi_init(void) { return 0; }
+
 static inline int register_acpi_bus_type(void *bus) { return 0; }
 static inline int unregister_acpi_bus_type(void *bus) { return 0; }