On 1/22/21 2:48 PM, David Hildenbrand wrote:

quoted

+/*
+ * Platforms should define arch_get_mappable_range() that provides
+ * maximum possible addressable physical memory range for which the
+ * linear mapping could be created. The platform returned address
+ * range must adhere to these following semantics.
+ *
+ * - range.start <= range.end
+ * - Range includes both end points [range.start..range.end]
+ *
+ * There is also a fallback definition provided here, allowing the
+ * entire possible physical address range in case any platform does
+ * not define arch_get_mappable_range().
+ */
+struct range __weak arch_get_mappable_range(void)
+{
+	struct range memhp_range = {
+		.start = 0UL,
+		.end = -1ULL,
+	};
+	return memhp_range;
+}
+
+struct range memhp_get_pluggable_range(bool need_mapping)
+{
+	const u64 max_phys = (1ULL << (MAX_PHYSMEM_BITS + 1)) - 1;

Sorry, thought about that line a bit more, and I think this is just
wrong (took me longer to realize as it should). The old code used this
calculation to print the limit only (in a wrong way), let's recap:

Assume MAX_PHYSMEM_BITS=32

	max_phys = (1ULL << (32 + 1)) - 1 = 0x1ffffffffull;

Ehm, these are 33 bit.

OTOH, old code checked for

	if (max_addr >> MAX_PHYSMEM_BITS) {

Which makes sense, because

	0x1ffffffffull >> 32 = 1

results in "true", meaning it's to big, while

	0xffffffffull >> 32 = 0

correctly results in "false", meaning the address is fine.



So, this should just be

const u64 max_phys = 1ULL << MAX_PHYSMEM_BITS;

(similarly as calculated in virito-mem code, or in kernel/resource.c)

Should this be 1ULL << MAX_PHYSMEM_BITS - 1 instead ? Currently there are
three usage for this variable in the function.

- if (mhp_range.start > max_phys)
- mhp_range.end = min_t(u64, mhp_range.end, max_phys)
- mhp_range.end = max_phys

mhp_range.end being always inclusive on the higher end and could be maximum
(1ULL << MAX_PHYSMEM_BITS - 1) which is 0xFFFFFFFF instead of 0x100000000
when (1ULL << MAX_PHYSMEM_BITS) is followed for a 32 bit system. This seems
consistent with the default fallback (range.end = -1ULL) defined above.

quoted

+	struct range memhp_range;
+
+	if (need_mapping) {
+		memhp_range = arch_get_mappable_range();
+		if (memhp_range.start > max_phys) {
+			memhp_range.start = 0;
+			memhp_range.end = 0;
+		}
+		memhp_range.end = min_t(u64, memhp_range.end, max_phys);
+	} else {
+		memhp_range.start = 0;
+		memhp_range.end = max_phys;
+	}
+	return memhp_range;
+}
+EXPORT_SYMBOL_GPL(memhp_get_pluggable_range);

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