x86/efi: Fix graceful fault handling after FPU softirq changes

commit 088f65e upstream.

Since commit d021985 ("x86/fpu: Improve crypto performance by
making kernel-mode FPU reliably usable in softirqs"), kernel_fpu_begin()
calls fpregs_lock() which uses local_bh_disable() instead of the
previous preempt_disable(). This sets SOFTIRQ_OFFSET in preempt_count
during the entire EFI runtime service call, causing in_interrupt() to
return true in normal task context.

The graceful page fault handler efi_crash_gracefully_on_page_fault()
uses in_interrupt() to bail out for faults in real interrupt context.
With SOFTIRQ_OFFSET now set, the handler always bails out, leaving EFI
firmware page faults unhandled. This escalates to die() which also sees
in_interrupt() as true and calls panic("Fatal exception in interrupt"),
resulting in a hard system freeze. On systems with buggy firmware that
triggers page faults during EFI runtime calls (e.g., accessing unmapped
memory in GetTime()), this causes an unrecoverable hang instead of the
expected graceful EFI_ABORTED recovery.

Fix by replacing in_interrupt() with !in_task(). This preserves the
original intent of bailing for interrupts or NMI faults, while no longer
falsely triggering from the FPU code path's local_bh_disable().

Fixes: d021985 ("x86/fpu: Improve crypto performance by making kernel-mode FPU reliably usable in softirqs")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ivan Hu <ivan.hu@canonical.com>
[ardb: Sashiko spotted that using 'in_hardirq() || in_nmi()' leaves a
       window where a softirq may be taken before fpregs_lock() is
       called, but after efi_rts_work.efi_rts_id has been assigned,
       and any page faults occurring in that window will then be
       misidentified as having been caused by the firmware. Instead,
       use !in_task(), which incorporates in_serving_softirq(). ]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Ivanhu5866

arch/x86/platform/efi/quirks.c

@@ -771,7 +771,7 @@ void efi_crash_gracefully_on_page_fault(unsigned long phys_addr,
 	 * If we get an interrupt/NMI while processing an EFI runtime service
 	 * then this is a regular OOPS, not an EFI failure.
 	 */
-	if (in_interrupt())
+	if (!in_task())
 		return;
 
 	/*