arm64/boot: Disable trapping of PMZR_EL0 writes to EL2grafted

__init_el2_fgt2() writes one mask to both HDFGRTR2_EL2 and HDFGWTR2_EL2.
PMZR_EL0 is write-only, so its trap bit, nPMZR_EL0, exists only in
HDFGWTR2_EL2 and is therefore never set: a PMZR_EL0 write from the host
traps to EL2, where the nVHE hypervisor has no handler and BUG()s. The
kernel never writes PMZR_EL0, but kernel.perf_user_access=1 has the PMU
driver set PMUSERENR_EL0.UEN for a task with a user-read event, so a
write from EL0 reaches the trap and takes the host down without a panic
message.

Accumulate the HDFGWTR2_EL2 bits separately, as __init_el2_fgt() already
does for HDFGWTR_EL2, and set nPMZR_EL0 with the other FEAT_PMUv3p9
bits.

Fixes: 858c7bfcb35e1 ("arm64/boot: Enable EL2 requirements for FEAT_PMUv3p9")
Cc: stable@vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/Documentation/input/notifier.rst b/Documentation/input/notifier.rst
new file mode 100644
index 000000000..824379399
--- /dev/null
+++ b/Documentation/input/notifier.rst
@@ -0,0 +1,55 @@
+=================
+Keyboard notifier
+=================
+
+One can use register_keyboard_notifier to get called back on keyboard
+events (see kbd_keycode() function for details).  The passed structure is
+keyboard_notifier_param (see <linux/keyboard.h>):
+
+- 'vc' always provide the VC for which the keyboard event applies;
+- 'down' is 1 for a key press event, 0 for a key release;
+- 'shift' is the current modifier state, mask bit indexes are KG_*;
+- 'ledstate' is the current LED state;
+- 'value' depends on the type of event.
+
+- KBD_KEYCODE events are always sent before other events, value is the keycode.
+- KBD_UNBOUND_KEYCODE events are sent if the keycode is not bound to a keysym.
+  value is the keycode.
+- KBD_UNICODE events are sent if the keycode -> keysym translation produced a
+  unicode character. value is the unicode value.
+- KBD_KEYSYM events are sent if the keycode -> keysym translation produced a
+  non-unicode character. value is the keysym.
+- KBD_POST_KEYSYM events are sent after the treatment of non-unicode keysyms.
+  That permits one to inspect the resulting LEDs for instance.
+
+For each kind of event but the last, the callback may return NOTIFY_STOP in
+order to "eat" the event: the notify loop is stopped and the keyboard event is
+dropped.
+
+In a rough C snippet, we have::
+
+    kbd_keycode(keycode) {
+	...
+	params.value = keycode;
+	if (notifier_call_chain(KBD_KEYCODE,&params) == NOTIFY_STOP)
+	    || !bound) {
+		notifier_call_chain(KBD_UNBOUND_KEYCODE,&params);
+		return;
+	}
+
+	if (unicode) {
+		param.value = unicode;
+		if (notifier_call_chain(KBD_UNICODE,&params) == NOTIFY_STOP)
+			return;
+		emit unicode;
+		return;
+	}
+
+	params.value = keysym;
+	if (notifier_call_chain(KBD_KEYSYM,&params) == NOTIFY_STOP)
+		return;
+	apply keysym;
+	notifier_call_chain(KBD_POST_KEYSYM,&params);
+    }
+
+.. note:: This notifier is usually called from interrupt context.