Commit b6eca183 authored by Leonardo Bras's avatar Leonardo Bras Committed by Michael Ellerman

powerpc/kernel: Enables memory hot-remove after reboot on pseries guests

While providing guests, it's desirable to resize it's memory on demand.

By now, it's possible to do so by creating a guest with a small base
memory, hot-plugging all the rest, and using 'movable_node' kernel
command-line parameter, which puts all hot-plugged memory in
ZONE_MOVABLE, allowing it to be removed whenever needed.

But there is an issue regarding guest reboot:
If memory is hot-plugged, and then the guest is rebooted, all hot-plugged
memory goes to ZONE_NORMAL, which offers no guaranteed hot-removal.
It usually prevents this memory to be hot-removed from the guest.

It's possible to use device-tree information to fix that behavior, as
it stores flags for LMB ranges on ibm,dynamic-memory-vN.
It involves marking each memblock with the correct flags as hotpluggable
memory, which mm/memblock.c puts in ZONE_MOVABLE during boot if
'movable_node' is passed.

For carrying such information, the new flag DRCONF_MEM_HOTREMOVABLE was
proposed and accepted into Power Architecture documentation.
This flag should be:
- true (b=1) if the hypervisor may want to hot-remove it later, and
- false (b=0) if it does not care.

During boot, guest kernel reads the device-tree, early_init_drmem_lmb()
is called for every added LMBs. Here, checking for this new flag and
marking memblocks as hotplugable memory is enough to get the desirable
behavior.

This should cause no change if 'movable_node' parameter is not passed
in kernel command-line.
Signed-off-by: default avatarLeonardo Bras <leonardo@linux.ibm.com>
Reviewed-by: default avatarBharata B Rao <bharata@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200402195156.626430-1-leonardo@linux.ibm.com
parent 0e7e92ef
...@@ -65,6 +65,7 @@ struct of_drconf_cell_v2 { ...@@ -65,6 +65,7 @@ struct of_drconf_cell_v2 {
#define DRCONF_MEM_ASSIGNED 0x00000008 #define DRCONF_MEM_ASSIGNED 0x00000008
#define DRCONF_MEM_AI_INVALID 0x00000040 #define DRCONF_MEM_AI_INVALID 0x00000040
#define DRCONF_MEM_RESERVED 0x00000080 #define DRCONF_MEM_RESERVED 0x00000080
#define DRCONF_MEM_HOTREMOVABLE 0x00000100
static inline u32 drmem_lmb_size(void) static inline u32 drmem_lmb_size(void)
{ {
......
...@@ -515,9 +515,14 @@ static void __init early_init_drmem_lmb(struct drmem_lmb *lmb, ...@@ -515,9 +515,14 @@ static void __init early_init_drmem_lmb(struct drmem_lmb *lmb,
size = 0x80000000ul - base; size = 0x80000000ul - base;
} }
if (!validate_mem_limit(base, &size))
continue;
DBG("Adding: %llx -> %llx\n", base, size); DBG("Adding: %llx -> %llx\n", base, size);
if (validate_mem_limit(base, &size))
memblock_add(base, size); memblock_add(base, size);
if (lmb->flags & DRCONF_MEM_HOTREMOVABLE)
memblock_mark_hotplug(base, size);
} while (--rngs); } while (--rngs);
} }
#endif /* CONFIG_PPC_PSERIES */ #endif /* CONFIG_PPC_PSERIES */
......
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