Commit 822c8020 authored by Michael Ellerman's avatar Michael Ellerman Committed by Damien Le Moal
Browse files

ata: pata_macio: Fix DMA table overflow 



Kolbjørn and Jonáš reported that their 32-bit PowerMacs were crashing
in pata-macio since commit 09fe2bfa ("ata: pata_macio: Fix
max_segment_size with PAGE_SIZE == 64K").

For example:

  kernel BUG at drivers/ata/pata_macio.c:544!
  Oops: Exception in kernel mode, sig: 5 [#1]
  BE PAGE_SIZE=4K MMU=Hash SMP NR_CPUS=2 DEBUG_PAGEALLOC PowerMac
  ...
  NIP pata_macio_qc_prep+0xf4/0x190
  LR  pata_macio_qc_prep+0xfc/0x190
  Call Trace:
    0xc1421660 (unreliable)
    ata_qc_issue+0x14c/0x2d4
    __ata_scsi_queuecmd+0x200/0x53c
    ata_scsi_queuecmd+0x50/0xe0
    scsi_queue_rq+0x788/0xb1c
    __blk_mq_issue_directly+0x58/0xf4
    blk_mq_plug_issue_direct+0x8c/0x1b4
    blk_mq_flush_plug_list.part.0+0x584/0x5e0
    __blk_flush_plug+0xf8/0x194
    __submit_bio+0x1b8/0x2e0
    submit_bio_noacct_nocheck+0x230/0x304
    btrfs_work_helper+0x200/0x338
    process_one_work+0x1a8/0x338
    worker_thread+0x364/0x4c0
    kthread+0x100/0x104
    start_kernel_thread+0x10/0x14

That commit increased max_segment_size to 64KB, with the justification
that the SCSI core was already using that size when PAGE_SIZE == 64KB,
and that there was existing logic to split over-sized requests.

However with a sufficiently large request, the splitting logic causes
each sg to be split into two commands in the DMA table, leading to
overflow of the DMA table, triggering the BUG_ON().

With default settings the bug doesn't trigger, because the request size
is limited by max_sectors_kb == 1280, however max_sectors_kb can be
increased, and apparently some distros do that by default using udev
rules.

Fix the bug for 4KB kernels by reverting to the old max_segment_size.

For 64KB kernels the sg_tablesize needs to be halved, to allow for the
possibility that each sg will be split into two.

Fixes: 09fe2bfa ("ata: pata_macio: Fix max_segment_size with PAGE_SIZE == 64K")
Cc: stable@vger.kernel.org # v6.10+
Reported-by: default avatarKolbjørn Barmen <linux-ppc@kolla.no>
Closes: https://lore.kernel.org/all/62d248bb-e97a-25d2-bcf2-9160c518cae5@kolla.no/


Reported-by: default avatarJonáš Vidra <vidra@ufal.mff.cuni.cz>
Closes: https://lore.kernel.org/all/3b6441b8-06e6-45da-9e55-f92f2c86933e@ufal.mff.cuni.cz/


Tested-by: default avatarKolbjørn Barmen <linux-ppc@kolla.no>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: default avatarDamien Le Moal <dlemoal@kernel.org>
parent fa0db8e5

drivers/ata/pata_macio.c

+15 −8
Original line number Diff line number Diff line
@@ -208,6 +208,19 @@ static const char* macio_ata_names[] = { 
/* Don't let a DMA segment go all the way to 64K */

#define MAX_DBDMA_SEG		0xff00



#ifdef CONFIG_PAGE_SIZE_64KB

/*

 * The SCSI core requires the segment size to cover at least a page, so

 * for 64K page size kernels it must be at least 64K. However the

 * hardware can't handle 64K, so pata_macio_qc_prep() will split large

 * requests. To handle the split requests the tablesize must be halved.

 */

#define PATA_MACIO_MAX_SEGMENT_SIZE	SZ_64K

#define PATA_MACIO_SG_TABLESIZE		(MAX_DCMDS / 2)

#else

#define PATA_MACIO_MAX_SEGMENT_SIZE	MAX_DBDMA_SEG

#define PATA_MACIO_SG_TABLESIZE		MAX_DCMDS

#endif



/*

 * Wait 1s for disk to answer on IDE bus after a hard reset
@@ -912,16 +925,10 @@ static int pata_macio_do_resume(struct pata_macio_priv *priv) 


static const struct scsi_host_template pata_macio_sht = {

	__ATA_BASE_SHT(DRV_NAME),

	.sg_tablesize		= MAX_DCMDS,

	.sg_tablesize		= PATA_MACIO_SG_TABLESIZE,

	/* We may not need that strict one */

	.dma_boundary		= ATA_DMA_BOUNDARY,

	/*

	 * The SCSI core requires the segment size to cover at least a page, so

	 * for 64K page size kernels this must be at least 64K. However the

	 * hardware can't handle 64K, so pata_macio_qc_prep() will split large

	 * requests.

	 */

	.max_segment_size	= SZ_64K,

	.max_segment_size	= PATA_MACIO_MAX_SEGMENT_SIZE,

	.device_configure	= pata_macio_device_configure,

	.sdev_groups		= ata_common_sdev_groups,

	.can_queue		= ATA_DEF_QUEUE,