Hi Phaedrus,
On 07/04/2024 03:47, mwle...@mailtundra.com wrote:
Without this patch, when trying to boot zfs using U-Boot on a Jetson TX2
NX (which is aarch64), I get a CPU reset error like so:
"Synchronous Abort" handler, esr 0x96000021
elr: 00000000800c9000 lr : 00000000800c8ffc (reloc)
elr: 00000000fff77000 lr : 00000000fff76ffc
x0 : 00000000ffb40f04 x1 : 0000000000000000
x2 : 000000000000000a x3 : 0000000003100000
x4 : 0000000003100000 x5 : 0000000000000034
x6 : 00000000fff9cc6e x7 : 000000000000000f
x8 : 00000000ff7f84a0 x9 : 0000000000000008
x10: 00000000ffb40f04 x11: 0000000000000006
x12: 000000000001869f x13: 0000000000000001
x14: 00000000ff7f84bc x15: 0000000000000010
x16: 0000000000002080 x17: 00000000001fffff
x18: 00000000ff7fbdd8 x19: 00000000ffb405f8
x20: 00000000ffb40dd0 x21: 00000000fffabe5e
x22: 000000ea77940000 x23: 00000000ffb42090
x24: 0000000000000000 x25: 0000000000000000
x26: 0000000000000000 x27: 0000000000000000
x28: 0000000000bab10c x29: 00000000ff7f85f0
Code: d00001a0 9103a000 94006ac6 f9401ba0 (f9400000)
Resetting CPU ...
This happens when be64_to_cpu() is called on a value that exists at a
memory address that's 4 byte aligned but not 8 byte aligned (e.g. an
address ending in 04). The call stack where that happens is:
check_pool_label() ->
zfs_nvlist_lookup_uint64(vdevnvlist, ZPOOL_CONFIG_ASHIFT,...) ->
be64_to_cpu()
This is very odd, aarch64 doesn't generally have these restrictions. I
got a bit nerdsniped when I saw this so I did some digging and figured this:
1. Your abort exception doesn't include the FAR_ELx register (which
should contain the address that was being accessed when the abort
occured). This means your board is running in EL3.
2. It turns out there is an "A" flag in the SCTLR_ELx register, when set
this flag causes a fault when trying to load from an address that isn't
aligned to the size of the data element (see "A, bit" on
https://developer.arm.com/documentation/ddi0595/2021-06/AArch64-Registers/SCTLR-EL3--System-Control-Register--EL3-
I'm not sure who's in the "wrong" here, maybe the driver should avoid
unaligned accesses? But then again, I don't think you should be running
a ZFS driver in EL3.
I'm not familiar with the Jetson Nano, but maybe there's a documented
way to run U-Boot so that it isn't executing in EL3? Or if not you could
also try unsetting the A flag.
If this really is something to fix in the driver, I don't think
hotpatching every unaligned access with a malloc() is the right solution.
Signed-off-by: Phaedrus Leeds <mwle...@mailtundra.com>
Tested-by: Phaedrus Leeds <mwle...@mailtundra.com>
regarding your question about re-sending to remove these tags, I'd say
probably yes, and especially if you're going to send a new revision anyway.
fwiw you seem to have gotten pretty much everything else about the patch
submission process spot on :)
Kind regards,
---
fs/zfs/zfs.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/fs/zfs/zfs.c b/fs/zfs/zfs.c
index 61d58fce68..9a50deac18 100644
--- a/fs/zfs/zfs.c
+++ b/fs/zfs/zfs.c
@@ -1552,35 +1552,53 @@ nvlist_find_value(char *nvlist, char *name, int
valtype, char **val,
if (nelm_out)
*nelm_out = nelm;
return 1;
}
nvlist += encode_size; /* goto the next nvpair */
}
return 0;
}
+int is_word_aligned_ptr(void *ptr) {
+ return ((uintptr_t)ptr & (sizeof(void *) - 1)) == 0;
+}
+
int
zfs_nvlist_lookup_uint64(char *nvlist, char *name, uint64_t *out)
{
char *nvpair;
size_t size;
int found;
found = nvlist_find_value(nvlist, name, DATA_TYPE_UINT64, &nvpair, &size, 0);
if (!found)
return 0;
if (size < sizeof(uint64_t)) {
printf("invalid uint64\n");
return ZFS_ERR_BAD_FS;
}
+ /* On arm64, calling be64_to_cpu() on a value stored at a memory address
+ * that's not 8-byte aligned causes the CPU to reset. Avoid that by
copying the
+ * value somewhere else if needed.
+ */
+ if (!is_word_aligned_ptr((void *)nvpair)) {
+ uint64_t *alignedptr = malloc(sizeof(uint64_t));
+ if (!alignedptr)
+ return 0;
+ memcpy(alignedptr, nvpair, sizeof(uint64_t));
+ *out = be64_to_cpu(*alignedptr);
+ free(alignedptr);
+ return 1;
+ }
+
*out = be64_to_cpu(*(uint64_t *) nvpair);
return 1;
}
char *
zfs_nvlist_lookup_string(char *nvlist, char *name)
{
char *nvpair;
char *ret;
size_t slen;
--
// Caleb (they/them)
