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Commit ab3da156 authored by Ard Biesheuvel's avatar Ard Biesheuvel
Browse files

ARM: be strict about FP exceptions in kernel mode 



The support code in vfp_support_entry does not care whether the
exception that caused it to be invoked occurred in kernel mode or
in user mode. However, neither condition that could trigger this
exception (lazy restore and VFP bounce to support code) is
currently allowable in kernel mode.

In either case, print a message describing the condition before
letting the undefined instruction handler run its course and trigger
an oops.

Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: default avatarNicolas Pitre <nico@linaro.org>
parent 0773d73d

arch/arm/vfp/vfphw.S

+5 −0
Original line number Diff line number Diff line
@@ -78,6 +78,11 @@ 
ENTRY(vfp_support_entry)

	DBGSTR3	"instr %08x pc %08x state %p", r0, r2, r10



	ldr	r3, [sp, #S_PSR]	@ Neither lazy restore nor FP exceptions

	and	r3, r3, #MODE_MASK	@ are supported in kernel mode

	teq	r3, #USR_MODE

	bne	vfp_kmode_exception	@ Returns through lr



	VFPFMRX	r1, FPEXC		@ Is the VFP enabled?

	DBGSTR1	"fpexc %08x", r1

	tst	r1, #FPEXC_EN

arch/arm/vfp/vfpmodule.c

+20 −0
Original line number Diff line number Diff line
@@ -648,6 +648,26 @@ static int vfp_hotplug(struct notifier_block *b, unsigned long action, 
	return NOTIFY_OK;

}



void vfp_kmode_exception(void)

{

	/*

	 * If we reach this point, a floating point exception has been raised

	 * while running in kernel mode. If the NEON/VFP unit was enabled at the

	 * time, it means a VFP instruction has been issued that requires

	 * software assistance to complete, something which is not currently

	 * supported in kernel mode.

	 * If the NEON/VFP unit was disabled, and the location pointed to below

	 * is properly preceded by a call to kernel_neon_begin(), something has

	 * caused the task to be scheduled out and back in again. In this case,

	 * rebuilding and running with CONFIG_DEBUG_ATOMIC_SLEEP enabled should

	 * be helpful in localizing the problem.

	 */

	if (fmrx(FPEXC) & FPEXC_EN)

		pr_crit("BUG: unsupported FP instruction in kernel mode\n");

	else

		pr_crit("BUG: FP instruction issued in kernel mode with FP unit disabled\n");

}



/*

 * VFP support code initialisation.

 */