[PATCH v2 16/18] riscv: mm: Use physical memory aliases to apply PMAs

[Emil Renner Berthing]

Samuel Holland wrote:
> Hi Emil,
>
> Thanks for testing!
>
> On 2025-10-10 10:06 AM, Emil Renner Berthing wrote:
> > Samuel Holland wrote:
[ .. ]
> >> +
> >> +void __init riscv_init_memory_alias(void)
> >> +{
> >> +	int na = of_n_addr_cells(of_root);
> >> +	int ns = of_n_size_cells(of_root);
> >> +	int nc = na + ns + 2;
> >> +	const __be32 *prop;
> >> +	int pairs = 0;
> >> +	int len;
> >> +
> >> +	prop = of_get_property(of_root, "riscv,physical-memory-regions", &len);
> >> +	if (!prop)
> >> +		return;
> >> +
> >> +	len /= sizeof(__be32);
> >> +	for (int i = 0; len >= nc; i++, prop += nc, len -= nc) {
> >> +		unsigned long base = of_read_ulong(prop, na);
> >> +		unsigned long size = of_read_ulong(prop + na, ns);
> >> +		unsigned long flags = be32_to_cpup(prop + na + ns);
> >> +		struct memory_alias_pair *pair;
> >> +		int alias;
> >> +
> >> +		/* We only care about non-coherent memory. */
> >> +		if ((flags & PMA_ORDER_MASK) != PMA_ORDER_MEMORY || (flags & PMA_COHERENT))
> >> +			continue;
> >> +
> >> +		/* The cacheable alias must be usable memory. */
> >> +		if ((flags & PMA_CACHEABLE) &&
> >> +		    !memblock_overlaps_region(&memblock.memory, base, size))
> >> +			continue;
> >> +
> >> +		alias = FIELD_GET(PMR_ALIAS_MASK, flags);
> >> +		if (alias) {
> >> +			pair = NULL;
> >> +			for (int j = 0; j < pairs; j++) {
> >> +				if (alias == memory_alias_pairs[j].index) {
> >> +					pair = &memory_alias_pairs[j];
> >> +					break;
> >> +				}
> >> +			}
> >> +			if (!pair)
> >> +				continue;
> >> +		} else {
> >> +			/* Leave room for the null sentinel. */
> >> +			if (pairs == ARRAY_SIZE(memory_alias_pairs) - 1)
> >> +				continue;
> >> +			pair = &memory_alias_pairs[pairs++];
> >> +			pair->index = i;
> >
> > I think this needs to be pair->index = i + 1, so PMA_ALIAS(1) can refer to the
> > first entry (i = 0).
>
> The code here is as intended. It's the PMA_ALIAS(1) in the DT that I should have
> changed to PMA_ALIAS(0) after I removed the special first entry from the
> riscv,physical-memory-regions property. Patch 18 also needs this fix.

Hmm.. that doesn't quite work for me though. Then the "if (alias)" above won't
trigger with PMR_ALIAS(0) right?

/Emil