From c1f0616124c455c5c762b6f123e40bba5df759e6 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Sun, 16 May 2021 18:17:55 +0200
Subject: [PATCH] ALSA: intel8x0: Don't update period unless prepared
Git-commit: c1f0616124c455c5c762b6f123e40bba5df759e6
Patch-mainline: v5.13-rc3
References: git-fixes

The interrupt handler of intel8x0 calls snd_intel8x0_update() whenever
the hardware sets the corresponding status bit for each stream.  This
works fine for most cases as long as the hardware behaves properly.
But when the hardware gives a wrong bit set, this leads to a zero-
division Oops, and reportedly, this seems what happened on a VM.

For fixing the crash, this patch adds a internal flag indicating that
the stream is ready to be updated, and check it (as well as the flag
being in suspended) to ignore such spurious update.

Cc: <stable@vger.kernel.org>
Reported-and-tested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Link: https://lore.kernel.org/r/s5h5yzi7uh0.wl-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

---
 sound/pci/intel8x0.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/sound/pci/intel8x0.c
+++ b/sound/pci/intel8x0.c
@@ -354,6 +354,7 @@ struct ichdev {
 	unsigned int ali_slot;			/* ALI DMA slot */
 	struct ac97_pcm *pcm;
 	int pcm_open_flag;
+	unsigned int prepared:1;
 	unsigned int suspended: 1;
 };
 
@@ -714,6 +715,9 @@ static inline void snd_intel8x0_update(s
 	int status, civ, i, step;
 	int ack = 0;
 
+	if (!ichdev->prepared || ichdev->suspended)
+		return;
+
 	spin_lock_irqsave(&chip->reg_lock, flags);
 	status = igetbyte(chip, port + ichdev->roff_sr);
 	civ = igetbyte(chip, port + ICH_REG_OFF_CIV);
@@ -907,6 +911,7 @@ static int snd_intel8x0_hw_params(struct
 	if (ichdev->pcm_open_flag) {
 		snd_ac97_pcm_close(ichdev->pcm);
 		ichdev->pcm_open_flag = 0;
+		ichdev->prepared = 0;
 	}
 	err = snd_ac97_pcm_open(ichdev->pcm, params_rate(hw_params),
 				params_channels(hw_params),
@@ -928,6 +933,7 @@ static int snd_intel8x0_hw_free(struct s
 	if (ichdev->pcm_open_flag) {
 		snd_ac97_pcm_close(ichdev->pcm);
 		ichdev->pcm_open_flag = 0;
+		ichdev->prepared = 0;
 	}
 	return snd_pcm_lib_free_pages(substream);
 }
@@ -1002,6 +1008,7 @@ static int snd_intel8x0_pcm_prepare(stru
 			ichdev->pos_shift = (runtime->sample_bits > 16) ? 2 : 1;
 	}
 	snd_intel8x0_setup_periods(chip, ichdev);
+	ichdev->prepared = 1;
 	return 0;
 }