Added quirk for Surface Go touchscreen - #100

With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we
get:

BUG: scheduling while atomic: swapper/1/0/0x00000000
no locks held by swapper/1/0.
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ linux-surface#100
Call Trace:
 dump_stack_lvl+0xac/0x108
 __schedule_bug+0xac/0xe0
 __schedule+0xcf8/0x10d0
 schedule_idle+0x3c/0x70
 do_idle+0x2d8/0x4a0
 cpu_startup_entry+0x38/0x40
 start_secondary+0x2ec/0x3a0
 start_secondary_prolog+0x10/0x14

This is because powerpc's arch_cpu_idle_dead() decrements the idle task's
preempt count, for reasons explained in commit a7c2bb8 ("powerpc:
Re-enable preemption before cpu_die()"), specifically "start_secondary()
expects a preempt_count() of 0."

However, since commit 2c669ef ("powerpc/preempt: Don't touch the idle
task's preempt_count during hotplug") and commit f1a0a37 ("sched/core:
Initialize the idle task with preemption disabled"), that justification no
longer holds.

The idle task isn't supposed to re-enable preemption, so remove the
vestigial preempt_enable() from the CPU offline path.

Tested with pseries and powernv in qemu, and pseries on PowerVM.

Fixes: 2c669ef ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug")
Signed-off-by: Nathan Lynch <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Reviewed-by: Srikar Dronamraju <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

[ Upstream commit 787252a ]

With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we
get:

BUG: scheduling while atomic: swapper/1/0/0x00000000
no locks held by swapper/1/0.
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100
Call Trace:
 dump_stack_lvl+0xac/0x108
 __schedule_bug+0xac/0xe0
 __schedule+0xcf8/0x10d0
 schedule_idle+0x3c/0x70
 do_idle+0x2d8/0x4a0
 cpu_startup_entry+0x38/0x40
 start_secondary+0x2ec/0x3a0
 start_secondary_prolog+0x10/0x14

This is because powerpc's arch_cpu_idle_dead() decrements the idle task's
preempt count, for reasons explained in commit a7c2bb8 ("powerpc:
Re-enable preemption before cpu_die()"), specifically "start_secondary()
expects a preempt_count() of 0."

However, since commit 2c669ef ("powerpc/preempt: Don't touch the idle
task's preempt_count during hotplug") and commit f1a0a37 ("sched/core:
Initialize the idle task with preemption disabled"), that justification no
longer holds.

The idle task isn't supposed to re-enable preemption, so remove the
vestigial preempt_enable() from the CPU offline path.

Tested with pseries and powernv in qemu, and pseries on PowerVM.

Fixes: 2c669ef ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug")
Signed-off-by: Nathan Lynch <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Reviewed-by: Srikar Dronamraju <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sasha Levin <[email protected]>

[BUG]
Recently, we encountered a KASAN warning as follows:

BUG: KASAN: slab-out-of-bounds in fb_pad_aligned_buffer+0x11f/0x140
Read of size 1 at addr ff1100015fd9f6a4 by task tty_fbcon_oob/1239
CPU: 7 UID: 0 PID: 1239 Comm: tty_fbcon_oob Not tainted 7.3.0-rc1 linux-surface#100 PREEMPT(full)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014
Call Trace:
 <TASK>
 ...
 kasan_report+0xf0/0x120
 fb_pad_aligned_buffer+0x11f/0x140
 ccw_putcs+0x86c/0xa80
 fbcon_putcs+0x338/0x410
 do_update_region+0x21d/0x450
 do_con_write+0x1e0e/0x4880
 con_write+0x13/0x80
 n_tty_write+0x374/0x1010
 file_tty_write.isra.0+0x404/0x7a0
 ...

reproduce:
1) open /dev/tty0, set a KDFONTOP ioctl with op.op = KD_FONT_OP_SET,
op.width = 8 and op.height = 16 (visible VC1)
2) open /dev/tty1, set a KDFONTOP ioctl with op.op = KD_FONT_OP_SET,
op.width = 28 and op.height = 24 (invisible VC2)
3) echo 3 > /sys/devices/virtual/graphics/fbcon/rotate_all
4) write EShash8(esc hash8) to tty1

[CAUSE]
All VCs render to the framebuffer. setfont only modifies the target VC's
font without resizing the framebuffer backing buffer (par->rotated.buf);
the buffer is only resized for the visible VC
(fbcon_do_set_font -> ... -> vc_do_resize -> update_screen). This relies on
the con_should_update() check performed before every update_region().

However, the ESC # 8 path (do_con_trol -> do_update_region) omits the
con_should_update() check. After changing the font size of an invisible VC,
do_update_region() fills using the new font size against a buffer that was
never resized, causing an out-of-bounds access.

[FIX]
Only push the update when the console is visible and not blanked, add
the con_should_update() check in the do_con_trol() like every other call
site of do_update_region() (update_region(), invert_screen(), ...).

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable <[email protected]>
Signed-off-by: Zizhi Wo <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>