It does not need much, just skip populating kernel linear mapping
for range of un-addressable device memory (it is pick so that there
is no physical memory resource overlapping it). All the logic is in
share mm code.
Only support x86-64 as this feature doesn't make much sense with
constrained virtual address space of 32bits architecture.
Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
---
arch/x86/mm/init_64.c | 28 ++++++++++++++--------------
1 file changed, 14 insertions(+), 14 deletions(-)
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 8c4abb0..556f7bb 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -661,13 +661,17 @@ int arch_add_memory(int nid, u64 start, u64 size, int flags)
unsigned long nr_pages = size >> PAGE_SHIFT;
int ret;
- /* Need to add support for device and unaddressable memory if needed */
- if (flags & MEMORY_UNADDRESSABLE) {
- BUG();
- return -EINVAL;
- }
-
- init_memory_mapping(start, start + size);
+ /*
+ * We get un-addressable memory when some one is adding a ZONE_DEVICE
+ * to have struct page for a device memory which is not accessible by
+ * the CPU so it is pointless to have a linear kernel mapping of such
+ * memory.
+ *
+ * Core mm should make sure it never set a pte pointing to such fake
+ * physical range.
+ */
+ if (!(flags & MEMORY_UNADDRESSABLE))
+ init_memory_mapping(start, start + size);
ret = __add_pages(nid, zone, start_pfn, nr_pages);
WARN_ON_ONCE(ret);
@@ -972,12 +976,6 @@ int __ref arch_remove_memory(u64 start, u64 size, int flags)
struct zone *zone;
int ret;
- /* Need to add support for device and unaddressable memory if needed */
- if (flags & MEMORY_UNADDRESSABLE) {
- BUG();
- return -EINVAL;
- }
-
/* With altmap the first mapped page is offset from @start */
altmap = to_vmem_altmap((unsigned long) page);
if (altmap)
@@ -985,7 +983,9 @@ int __ref arch_remove_memory(u64 start, u64 size, int flags)
zone = page_zone(page);
ret = __remove_pages(zone, start_pfn, nr_pages);
WARN_ON_ONCE(ret);
- kernel_physical_mapping_remove(start, start + size);
+
+ if (!(flags & MEMORY_UNADDRESSABLE))
+ kernel_physical_mapping_remove(start, start + size);
return ret;
}
--
2.4.3
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