linux-kernel - [PATCH] ARM: vfp: Add vudot opcode to VFP undef hook

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Date:   Wed, 20 Sep 2023 16:39:00 +0800
From:   Mark-PK Tsai <mark-pk.tsai@...iatek.com>
To:     Russell King <linux@...linux.org.uk>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
CC:     <yj.chiang@...iatek.com>, Mark-PK Tsai <mark-pk.tsai@...iatek.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: [PATCH] ARM: vfp: Add vudot opcode to VFP undef hook

Add vudot opcode to the VFP undef hook to fix the
potentially undefined instruction error when the
user space executes vudot instruction.

Before this commit, kernel didn't handle the undef exception
caused by vudot and didn't enable VFP in lazy VFP context
switch code like other NEON instructions.
This led to the occurrence of the undefined instruction
error as following:

[  250.741238 ] 0904 (26902): undefined instruction: pc=004014ec
...
[  250.741287 ] PC is at 0x4014ec
[  250.741298 ] LR is at 0xb677874f
[  250.741303 ] pc : [<004014ec>]    lr : [<b677874f>]    psr: 80070010
[  250.741309 ] sp : beffedb0  ip : b67d7864  fp : beffee58
[  250.741314 ] r10: 00000000  r9 : 00000000  r8 : 00000000
[  250.741319 ] r7 : 00000001  r6 : 00000001  r5 : beffee90  r4 : 00401470
[  250.741324 ] r3 : beffee20  r2 : beffee30  r1 : beffee40  r0 : 004003a8
[  250.741331 ] Flags: Nzcv  IRQs on  FIQs on  Mode USER_32  ISA ARM Segment user
[  250.741339 ] Control: 10c5383d  Table: 32d0406a  DAC: 00000055
[  250.741348 ] Code: f4434aef f4610aef f4622aef f4634aef (fc620df4)

Below is the assembly of the user program:

0x4014dc <+108>: vst1.64 {d20, d21}, [r3:128]
0x4014e0 <+112>: vld1.64 {d16, d17}, [r1:128]
0x4014e4 <+116>: vld1.64 {d18, d19}, [r2:128]
0x4014e8 <+120>: vld1.64 {d20, d21}, [r3:128] --> switch out
0x4014ec <+124>: vudot.u8 q8, q9, q10         <-- switch in, and FPEXC.EN = 0
                                                  SIGILL(illegal instruction)

Link: https://services.arm.com/support/s/case/5004L00000XsOjP
Signed-off-by: Mark-PK Tsai <mark-pk.tsai@...iatek.com>
---
 arch/arm/vfp/vfpmodule.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 7e8773a2d99d..7eab8d1019d2 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -788,6 +788,12 @@ static struct undef_hook neon_support_hook[] = {{
 	.cpsr_mask	= PSR_T_BIT,
 	.cpsr_val	= 0,
 	.fn		= vfp_support_entry,
+}, {
+	.instr_mask	= 0xffb00000,
+	.instr_val	= 0xfc200000,
+	.cpsr_mask	= PSR_T_BIT,
+	.cpsr_val	= 0,
+	.fn		= vfp_support_entry,
 }, {
 	.instr_mask	= 0xef000000,
 	.instr_val	= 0xef000000,
@@ -800,6 +806,12 @@ static struct undef_hook neon_support_hook[] = {{
 	.cpsr_mask	= PSR_T_BIT,
 	.cpsr_val	= PSR_T_BIT,
 	.fn		= vfp_support_entry,
+}, {
+	.instr_mask	= 0xffb00000,
+	.instr_val	= 0xfc200000,
+	.cpsr_mask	= PSR_T_BIT,
+	.cpsr_val	= PSR_T_BIT,
+	.fn		= vfp_support_entry,
 }};
 
 static struct undef_hook vfp_support_hook = {
-- 
2.18.0