On Thu, 25 Apr 2024 at 11:58, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> And maybe this time, it's not a buggy mess?
Actually, even with MASK_VAL() fixed, I think it's *STILL* a buggy mess.
Why? Beuse the *uses* of MASK_VAL() seem entirely bogus.
In particular, we have this in cpc_write():
if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
val = MASK_VAL(reg, val);
switch (size) {
case 8:
writeb_relaxed(val, vaddr);
break;
case 16:
writew_relaxed(val, vaddr);
break;
...
and I strongly suspect that it needs to update the 'vaddr' too. Something like
if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
val = MASK_VAL(reg, val);
#ifdef __LITTLE_ENDIAN
vaddr += reg->bit_offset >> 3;
if (reg->bit_offset & 7)
return -EFAULT;
#else
/* Fixme if we ever care */
if (reg->bit_offset)
return -EFAULT;
#endif
}
*might* be changing this in the right direction, but it's unclear and
I neither know that CPC rules, nor did I think _that_ much about it.
Anyway, the take-away should be that all this code is entirely broken
and somebody didn't think enough about it.
It's possible that that whole cpc_write() ACPI_ADR_SPACE_SYSTEM_MEMORY
case should be done as a 64-bit "read-mask-write" sequence.
Possibly with "reg->bit_offset == 0" and the 8/16/32/64-bit cases as a
special case for "just do the write".
Or, maybe writes with a non-zero bit offset shouldn't be allowed at
all, and there are CPC rules that aren't checked. I don't know. I only
know that the current code is seriously broken.
Linus
