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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.

Change-Id: I1a9508f3adfb0264cac1984d6080d117bfcb39f6
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
This commit is contained in:
Ard Biesheuvel 2013-05-24 16:23:28 +02:00 committed by Dan Pasanen
parent 3dab984695
commit d74abc2b4f
2 changed files with 25 additions and 0 deletions
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5
arch/arm/vfp/vfphw.S
View File

@ -71,6 +71,11 @@
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

20
arch/arm/vfp/vfpmodule.c
View File

@ -675,6 +675,26 @@ static int proc_read_status(char *page, char **start, off_t off, int count,
}
#endif
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.
*/