On Mon, 2014-11-17 at 18:42 +0100, Greg Kurz wrote:
> The first argument to vphn_unpack_associativity() is a const long *, but the
> parsing code expects __be64 values actually. This is inconsistent. We should
> either pass a const __be64 * or change vphn_unpack_associativity() so that
> it fixes endianness by itself.
>
> This patch does the latter, since the caller doesn't need to know about
> endianness and this allows to fix significant 64-bit values only. Please
> note that the previous code was able to cope with 32-bit fields being split
> accross two consecutives 64-bit values. Since PAPR+ doesn't say this cannot
> happen, the behaviour was kept. It requires extra checking to know when fixing
> is needed though.
While I agree with moving the endian fixing down, the patch makes me
nervous. Note that I don't fully understand the format of what we are
parsing here so I might be wrong but ...
>
> #define VPHN_FIELD_UNUSED (0xffff)
> #define VPHN_FIELD_MSB (0x8000)
> #define VPHN_FIELD_MASK (~VPHN_FIELD_MSB)
>
> - for (i = 1; i < VPHN_ASSOC_BUFSIZE; i++) {
> - if (be16_to_cpup(field) == VPHN_FIELD_UNUSED)
> + for (i = 1, j = 0, k = 0; i < VPHN_ASSOC_BUFSIZE;) {
> + u16 field;
> +
> + if (j % 4 == 0) {
> + fixed.packed[k] = cpu_to_be64(packed[k]);
> + k++;
> + }
So we have essentially a bunch of 16-bit fields ... the above loads and
swap a whole 4 of them at once. However that means not only we byteswap
them individually, but we also flip the order of the fields. This is
ok ?
> + field = be16_to_cpu(fixed.field[j]);
> +
> + if (field == VPHN_FIELD_UNUSED)
> /* All significant fields processed.
> */
> break;
For example, we might have USED,USED,USED,UNUSED ... after the swap, we
now have UNUSED,USED,USED,USED ... and we stop parsing in the above
line on the first one. Or am I missing something ?
> - if (be16_to_cpup(field) & VPHN_FIELD_MSB) {
> + if (field & VPHN_FIELD_MSB) {
> /* Data is in the lower 15 bits of this field */
> - unpacked[i] = cpu_to_be32(
> - be16_to_cpup(field) & VPHN_FIELD_MASK);
> - field++;
> + unpacked[i++] = cpu_to_be32(field & VPHN_FIELD_MASK);
> + j++;
> } else {
> /* Data is in the lower 15 bits of this field
> * concatenated with the next 16 bit field
> */
> - unpacked[i] = *((__be32 *)field);
> - field += 2;
> + if (unlikely(j % 4 == 3)) {
> + /* The next field is to be copied from the next
> + * 64-bit input value. We must fix it now.
> + */
> + fixed.packed[k] = cpu_to_be64(packed[k]);
> + k++;
> + }
> +
> + unpacked[i++] = *((__be32 *)&fixed.field[j]);
> + j += 2;
> }
> }
>
> @@ -1460,11 +1479,8 @@ static long hcall_vphn(unsigned long cpu, __be32
> *associativity)
> long retbuf[PLPAR_HCALL9_BUFSIZE] = {0};
> u64 flags = 1;
> int hwcpu = get_hard_smp_processor_id(cpu);
> - int i;
>
> rc = plpar_hcall9(H_HOME_NODE_ASSOCIATIVITY, retbuf, flags, hwcpu);
> - for (i = 0; i < VPHN_REGISTER_COUNT; i++)
> - retbuf[i] = cpu_to_be64(retbuf[i]);
> vphn_unpack_associativity(retbuf, associativity);
>
> return rc;
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