[PATCH v3] powerpc/memhotplug: Add add_pages override for PPC

[Aneesh Kumar K.V]

With commit ffa0b64e3be5 ("powerpc: Fix virt_addr_valid() for 64-bit Book3E & 32-bit")
the kernel now validate the addr against high_memory value. This results
in the below BUG_ON with dax pfns.

[  635.798741][T26531] kernel BUG at mm/page_alloc.c:5521!
1:mon> e
cpu 0x1: Vector: 700 (Program Check) at [c000000007287630]
    pc: c00000000055ed48: free_pages.part.0+0x48/0x110
    lr: c00000000053ca70: tlb_finish_mmu+0x80/0xd0
    sp: c0000000072878d0
   msr: 800000000282b033
  current = 0xc00000000afabe00
  paca    = 0xc00000037ffff300   irqmask: 0x03   irq_happened: 0x05
    pid   = 26531, comm = 50-landscape-sy
kernel BUG at :5521!
Linux version 5.19.0-rc3-14659-g4ec05be7c2e1 (kvaneesh at ltc-boston8) (gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #625 SMP Thu Jun 23 00:35:43 CDT 2022
1:mon> t
[link register   ] c00000000053ca70 tlb_finish_mmu+0x80/0xd0
[c0000000072878d0] c00000000053ca54 tlb_finish_mmu+0x64/0xd0 (unreliable)
[c000000007287900] c000000000539424 exit_mmap+0xe4/0x2a0
[c0000000072879e0] c00000000019fc1c mmput+0xcc/0x210
[c000000007287a20] c000000000629230 begin_new_exec+0x5e0/0xf40
[c000000007287ae0] c00000000070b3cc load_elf_binary+0x3ac/0x1e00
[c000000007287c10] c000000000627af0 bprm_execve+0x3b0/0xaf0
[c000000007287cd0] c000000000628414 do_execveat_common.isra.0+0x1e4/0x310
[c000000007287d80] c00000000062858c sys_execve+0x4c/0x60
[c000000007287db0] c00000000002c1b0 system_call_exception+0x160/0x2c0
[c000000007287e10] c00000000000c53c system_call_common+0xec/0x250

The fix is to make sure we update high_memory on memory hotplug.
This is similar to what x86 does in commit 3072e413e305 ("mm/memory_hotplug: introduce add_pages")

Fixes: ffa0b64e3be5 ("powerpc: Fix virt_addr_valid() for 64-bit Book3E & 32-bit")
Cc: Kefeng Wang <wangkefeng.wang at huawei.com>
Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
---
Changes from v2:
* drop WARN_ON_ONCE
* check for error from __add_pages

 arch/powerpc/Kconfig  |  4 ++++
 arch/powerpc/mm/mem.c | 33 ++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c2ce2e60c8f0..7aa12e88c580 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -358,6 +358,10 @@ config ARCH_SUSPEND_NONZERO_CPU
 	def_bool y
 	depends on PPC_POWERNV || PPC_PSERIES
 
+config ARCH_HAS_ADD_PAGES
+	def_bool y
+	depends on ARCH_ENABLE_MEMORY_HOTPLUG
+
 config PPC_DCR_NATIVE
 	bool
 
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 52b77684acda..a97128a48817 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -105,6 +105,37 @@ void __ref arch_remove_linear_mapping(u64 start, u64 size)
 	vm_unmap_aliases();
 }
 
+/*
+ * After memory hotplug the variables max_pfn, max_low_pfn and high_memory need
+ * updating.
+ */
+static void update_end_of_memory_vars(u64 start, u64 size)
+{
+	unsigned long end_pfn = PFN_UP(start + size);
+
+	if (end_pfn > max_pfn) {
+		max_pfn = end_pfn;
+		max_low_pfn = end_pfn;
+		high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
+	}
+}
+
+int __ref add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
+		    struct mhp_params *params)
+{
+	int ret;
+
+	ret = __add_pages(nid, start_pfn, nr_pages, params);
+	if (ret)
+		return ret;
+
+	/* update max_pfn, max_low_pfn and high_memory */
+	update_end_of_memory_vars(start_pfn << PAGE_SHIFT,
+				  nr_pages << PAGE_SHIFT);
+
+	return ret;
+}
+
 int __ref arch_add_memory(int nid, u64 start, u64 size,
 			  struct mhp_params *params)
 {
@@ -115,7 +146,7 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
 	rc = arch_create_linear_mapping(nid, start, size, params);
 	if (rc)
 		return rc;
-	rc = __add_pages(nid, start_pfn, nr_pages, params);
+	rc = add_pages(nid, start_pfn, nr_pages, params);
 	if (rc)
 		arch_remove_linear_mapping(start, size);
 	return rc;
-- 
2.36.1