linux-kernel - Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online

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Date:   Fri, 14 Jun 2019 14:28:40 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Qian Cai <cai@....pw>, Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()

Qian Cai <cai@....pw> writes:


> 1) offline is busted [1]. It looks like test_pages_in_a_zone() missed the same
> pfn_section_valid() check.
>
> 2) powerpc booting is generating endless warnings [2]. In vmemmap_populated() at
> arch/powerpc/mm/init_64.c, I tried to change PAGES_PER_SECTION to
> PAGES_PER_SUBSECTION, but it alone seems not enough.
>

Can you check with this change on ppc64.  I haven't reviewed this series yet.
I did limited testing with change . Before merging this I need to go
through the full series again. The vmemmap poplulate on ppc64 needs to
handle two translation mode (hash and radix). With respect to vmemap
hash doesn't setup a translation in the linux page table. Hence we need
to make sure we don't try to setup a mapping for a range which is
arleady convered by an existing mapping. 

diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index a4e17a979e45..15c342f0a543 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -88,16 +88,23 @@ static unsigned long __meminit vmemmap_section_start(unsigned long page)
  * which overlaps this vmemmap page is initialised then this page is
  * initialised already.
  */
-static int __meminit vmemmap_populated(unsigned long start, int page_size)
+static bool __meminit vmemmap_populated(unsigned long start, int page_size)
 {
 	unsigned long end = start + page_size;
 	start = (unsigned long)(pfn_to_page(vmemmap_section_start(start)));
 
-	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page)))
-		if (pfn_valid(page_to_pfn((struct page *)start)))
-			return 1;
+	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page))) {
 
-	return 0;
+		struct mem_section *ms;
+		unsigned long pfn = page_to_pfn((struct page *)start);
+
+		if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
+			return 0;
+		ms = __nr_to_section(pfn_to_section_nr(pfn));
+		if (valid_section(ms))
+			return true;
+	}
+	return false;
 }
 
 /*