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authorPaul Burton <paul.burton@imgtec.com>2016-09-23 15:13:53 +0100
committerRalf Baechle <ralf@linux-mips.org>2016-09-23 18:21:38 +0200
commit7e956304eb8a285304a78582e4537e72c6365f20 (patch)
treeec1742eefeaa9f7e785b79512516263411a14bcd /arch
parent554af0c396380baf416f54c439b99b495180b2f4 (diff)
downloadlinux-stericsson-7e956304eb8a285304a78582e4537e72c6365f20.tar.gz
MIPS: Fix pre-r6 emulation FPU initialisation
In the mipsr2_decoder() function, used to emulate pre-MIPSr6 instructions that were removed in MIPSr6, the init_fpu() function is called if a removed pre-MIPSr6 floating point instruction is the first floating point instruction used by the task. However, init_fpu() performs varous actions that rely upon not being migrated. For example in the most basic case it sets the coprocessor 0 Status.CU1 bit to enable the FPU & then loads FP register context into the FPU registers. If the task were to migrate during this time, it may end up attempting to load FP register context on a different CPU where it hasn't set the CU1 bit, leading to errors such as: do_cpu invoked from kernel context![#2]: CPU: 2 PID: 7338 Comm: fp-prctl Tainted: G D 4.7.0-00424-g49b0c82 #2 task: 838e4000 ti: 88d38000 task.ti: 88d38000 $ 0 : 00000000 00000001 ffffffff 88d3fef8 $ 4 : 838e4000 88d38004 00000000 00000001 $ 8 : 3400fc01 801f8020 808e9100 24000000 $12 : dbffffff 807b69d8 807b0000 00000000 $16 : 00000000 80786150 00400fc4 809c0398 $20 : 809c0338 0040273c 88d3ff28 808e9d30 $24 : 808e9d30 00400fb4 $28 : 88d38000 88d3fe88 00000000 8011a2ac Hi : 0040273c Lo : 88d3ff28 epc : 80114178 _restore_fp+0x10/0xa0 ra : 8011a2ac mipsr2_decoder+0xd5c/0x1660 Status: 1400fc03 KERNEL EXL IE Cause : 1080002c (ExcCode 0b) PrId : 0001a920 (MIPS I6400) Modules linked in: Process fp-prctl (pid: 7338, threadinfo=88d38000, task=838e4000, tls=766527d0) Stack : 00000000 00000000 00000000 88d3fe98 00000000 00000000 809c0398 809c0338 808e9100 00000000 88d3ff28 00400fc4 00400fc4 0040273c 7fb69e18 004a0000 004a0000 004a0000 7664add0 8010de18 00000000 00000000 88d3fef8 88d3ff28 808e9100 00000000 766527d0 8010e534 000c0000 85755000 8181d580 00000000 00000000 00000000 004a0000 00000000 766527d0 7fb69e18 004a0000 80105c20 ... Call Trace: [<80114178>] _restore_fp+0x10/0xa0 [<8011a2ac>] mipsr2_decoder+0xd5c/0x1660 [<8010de18>] do_ri+0x90/0x6b8 [<80105c20>] ret_from_exception+0x0/0x10 Fix this by disabling preemption around the call to init_fpu(), ensuring that it starts & completes on one CPU. Signed-off-by: Paul Burton <paul.burton@imgtec.com> Fixes: b0a668fb2038 ("MIPS: kernel: mips-r2-to-r6-emul: Add R2 emulator for MIPS R6") Cc: linux-mips@linux-mips.org Cc: stable@vger.kernel.org # v4.0+ Patchwork: https://patchwork.linux-mips.org/patch/14305/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/mips/kernel/mips-r2-to-r6-emul.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/mips/kernel/mips-r2-to-r6-emul.c b/arch/mips/kernel/mips-r2-to-r6-emul.c
index c3372cac6db2..0a7e10b5f9e3 100644
--- a/arch/mips/kernel/mips-r2-to-r6-emul.c
+++ b/arch/mips/kernel/mips-r2-to-r6-emul.c
@@ -1164,7 +1164,9 @@ fpu_emul:
regs->regs[31] = r31;
regs->cp0_epc = epc;
if (!used_math()) { /* First time FPU user. */
+ preempt_disable();
err = init_fpu();
+ preempt_enable();
set_used_math();
}
lose_fpu(1); /* Save FPU state for the emulator. */