powerpc/pseries: check DRCONF_MEM_RESERVED in lmb_is_removable()

DRCONF_MEM_RESERVED is a flag that represents the "Reserved Memory"
status in LOPAR v2.10, section 4.2.8. If a LMB is marked as reserved,
quoting LOPAR, "is not to be used or altered by the base OS". This flag
is read only in the kernel, being set by the firmware/hypervisor in the
DT. As an example, QEMU will set this flag in hw/ppc/spapr.c,
spapr_dt_dynamic_memory().

lmb_is_removable() does not check for DRCONF_MEM_RESERVED. This function
is used in dlpar_remove_lmb() as a guard before the removal logic. Since
it is failing to check for !RESERVED, dlpar_remove_lmb() will fail in a
later stage instead of failing in the validation when receiving a
reserved LMB as input.

lmb_is_removable() is also used in dlpar_memory_remove_by_count() to
evaluate if we have enough LMBs to complete the request. The missing
!RESERVED check in this case is causing dlpar_memory_remove_by_count()
to miscalculate the number of elegible LMBs for the removal, and can
make it error out later on instead of failing in the validation with the
'not enough LMBs to satisfy request' message.

Making a DRCONF_MEM_RESERVED check in lmb_is_removable() fixes all these
issues.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210512202809.95363-3-danielhb413@gmail.com

arch/powerpc/platforms/pseries/hotplug-memory.c

@@ -348,7 +348,8 @@ static int pseries_remove_mem_node(struct device_node *np)
 
 static bool lmb_is_removable(struct drmem_lmb *lmb)
 {
-	if (!(lmb->flags & DRCONF_MEM_ASSIGNED))
+	if ((lmb->flags & DRCONF_MEM_RESERVED) ||
+		!(lmb->flags & DRCONF_MEM_ASSIGNED))
 		return false;
 
 #ifdef CONFIG_FA_DUMP