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fix(drivers): query real HVC block capacity instead of hardcoding 512 GiB #13

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Merged
AprilNEA merged 1 commit into from
Jul 19, 2026
Merged

fix(drivers): query real HVC block capacity instead of hardcoding 512 GiB #13

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51 changes: 40 additions & 11 deletions drivers/arcbox_hvc_blk.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7,10 +7,11 @@
* on the host file, bypassing VirtIO queues entirely.
*
* SMCCC function IDs (vendor-specific range):
* 0xC2000000 ARCBOX_HVC_PROBE -- returns number of block devices
* 0xC2000001 ARCBOX_HVC_BLK_READ -- synchronous pread
* 0xC2000002 ARCBOX_HVC_BLK_WRITE -- synchronous pwrite
* 0xC2000003 ARCBOX_HVC_BLK_FLUSH -- fsync
* 0xC2000000 ARCBOX_HVC_PROBE -- returns number of block devices
* 0xC2000001 ARCBOX_HVC_BLK_READ -- synchronous pread
* 0xC2000002 ARCBOX_HVC_BLK_WRITE -- synchronous pwrite
* 0xC2000003 ARCBOX_HVC_BLK_FLUSH -- fsync
* 0xC2000004 ARCBOX_HVC_BLK_CAPACITY -- device capacity in 512B sectors
*/

#include <linux/blk-mq.h>
Expand All @@ -19,11 +20,18 @@
#include <linux/version.h>
#include <linux/arm-smccc.h>

#define ARCBOX_HVC_PROBE 0xC2000000
#define ARCBOX_HVC_BLK_READ 0xC2000001
#define ARCBOX_HVC_BLK_WRITE 0xC2000002
#define ARCBOX_HVC_BLK_FLUSH 0xC2000003
#define ARCBOX_HVC_SECTOR 512
#define ARCBOX_HVC_PROBE 0xC2000000
#define ARCBOX_HVC_BLK_READ 0xC2000001
#define ARCBOX_HVC_BLK_WRITE 0xC2000002
#define ARCBOX_HVC_BLK_FLUSH 0xC2000003
#define ARCBOX_HVC_BLK_CAPACITY 0xC2000004
#define ARCBOX_HVC_SECTOR 512

/*
* Fallback capacity for hosts that predate ARCBOX_HVC_BLK_CAPACITY: the old
* fixed placeholder (512 GiB in sectors). Only used when the query fails.
*/
#define ARCBOX_HVC_DEFAULT_SECTORS ((sector_t)1 << 30)

#define DRIVER_NAME "arcbox_hvc_blk"
#define MAX_DEVICES 8
Expand Down Expand Up @@ -58,6 +66,24 @@ static int arcbox_hvc_flush(unsigned int idx)
return (long)res.a0 < 0 ? (int)(long)res.a0 : 0;
}

/*
* Query the device's real capacity in sectors. Returns the fixed fallback if
* the host is older than ARCBOX_HVC_BLK_CAPACITY (negative/zero result), so an
* old host keeps its previous behavior; a current host reports the true size,
* which the guest must honor or Btrfs will reject a data disk whose metadata
* records a larger size.
*/
static sector_t arcbox_hvc_capacity(unsigned int idx)
{
struct arm_smccc_res res;

arm_smccc_1_1_hvc(ARCBOX_HVC_BLK_CAPACITY, idx, 0, 0, 0, 0, 0, 0, &res);

if ((long)res.a0 <= 0)
return ARCBOX_HVC_DEFAULT_SECTORS;
return (sector_t)res.a0;
}

static blk_status_t arcbox_queue_rq(struct blk_mq_hw_ctx *hctx,
const struct blk_mq_queue_data *bd)
{
Expand Down Expand Up @@ -153,8 +179,11 @@ static int arcbox_probe_one(int idx)
disk->fops = &arcbox_fops;
snprintf(disk->disk_name, DISK_NAME_LEN, "arcboxhvc%d", idx);

/* Large default capacity — VMM validates sector range. */
set_capacity(disk, (sector_t)1 << 30);
/* Use the host-reported capacity so the guest sees the true disk size.
* A hardcoded value that undershoots the backing file silently corrupts
* a Btrfs data disk whose metadata records the real (larger) size.
*/
set_capacity(disk, arcbox_hvc_capacity(idx));

err = add_disk(disk);
if (err) {
Expand Down
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