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Subject[HMM 04/16] mm/ZONE_DEVICE/x86: add support for un-addressable device memory
Date
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@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
arch/x86/mm/init_64.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 6c0b24e..b635636 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -658,6 +658,7 @@ int arch_add_memory(int nid, u64 start, u64 size, enum memory_type type)
case MEMORY_NORMAL:
break;
case MEMORY_DEVICE_PERSISTENT:
+ case MEMORY_DEVICE_UNADDRESSABLE:
for_device = true;
break;
default:
@@ -668,7 +669,17 @@ int arch_add_memory(int nid, u64 start, u64 size, enum memory_type type)
zone = pgdat->node_zones +
zone_for_memory(nid, start, size, ZONE_NORMAL, for_device);

- 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 (type != MEMORY_DEVICE_UNADDRESSABLE)
+ init_memory_mapping(start, start + size);

ret = __add_pages(nid, zone, start_pfn, nr_pages);
WARN_ON_ONCE(ret);
@@ -980,6 +991,7 @@ int __ref arch_remove_memory(u64 start, u64 size, enum memory_type type)
switch (type) {
case MEMORY_NORMAL:
case MEMORY_DEVICE_PERSISTENT:
+ case MEMORY_DEVICE_UNADDRESSABLE:
break;
default:
pr_err("hotplug unsupported memory type %d\n", type);
@@ -993,7 +1005,9 @@ int __ref arch_remove_memory(u64 start, u64 size, enum memory_type type)
zone = page_zone(page);
ret = __remove_pages(zone, start_pfn, nr_pages);
WARN_ON_ONCE(ret);
- kernel_physical_mapping_remove(start, start + size);
+
+ if (type != MEMORY_DEVICE_UNADDRESSABLE)
+ kernel_physical_mapping_remove(start, start + size);

return ret;
}
--
2.9.3
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