[PATCH 6.18 156/198] ALSA: ctxfi: Limit PTP to a single page

Greg Kroah-Hartman
2026-04-20T16:03:53Z

From: Harin Lee <me@harin.net>

commit e9418da50d9e5c496c22fe392e4ad74c038a94eb upstream.

Commit 391e69143d0a increased CT_PTP_NUM from 1 to 4 to support 256
playback streams, but the additional pages are not used by the card
correctly. The CT20K2 hardware already has multiple VMEM_PTPAL
registers, but using them separately would require refactoring the
entire virtual memory allocation logic.

ct_vm_map() always uses PTEs in vm->ptp[0].area regardless of
CT_PTP_NUM. On AMD64 systems, a single PTP covers 512 PTEs (2M). When
aggregate memory allocations exceed this limit, ct_vm_map() tries to
access beyond the allocated space and causes a page fault:

BUG: unable to handle page fault for address: ffffd4ae8a10a000
Oops: Oops: 0002 [#1] SMP PTI
RIP: 0010:ct_vm_map+0x17c/0x280 [snd_ctxfi]
Call Trace:
atc_pcm_playback_prepare+0x225/0x3b0
ct_pcm_playback_prepare+0x38/0x60
snd_pcm_do_prepare+0x2f/0x50
snd_pcm_action_single+0x36/0x90
snd_pcm_action_nonatomic+0xbf/0xd0
snd_pcm_ioctl+0x28/0x40
__x64_sys_ioctl+0x97/0xe0
do_syscall_64+0x81/0x610
entry_SYSCALL_64_after_hwframe+0x76/0x7e

Revert CT_PTP_NUM to 1. The 256 SRC_RESOURCE_NUM and playback_count
remain unchanged.

Fixes: 391e69143d0a ("ALSA: ctxfi: Bump playback substreams to 256")
Cc: stable@vger.kernel.org
Signed-off-by: Harin Lee <me@harin.net>
Link: https://patch.msgid.link/20260406074857.216034-1-me@harin.net
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/pci/ctxfi/ctvmem.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/pci/ctxfi/ctvmem.h
+++ b/sound/pci/ctxfi/ctvmem.h
@@ -15,7 +15,7 @@
#ifndef CTVMEM_H
#define CTVMEM_H

-#define CT_PTP_NUM 4 /* num of device page table pages */
+#define CT_PTP_NUM 1 /* num of device page table pages */

#include <linux/mutex.h>
#include <linux/list.h>