linux-kernel - [RFC PATCH 6/6] arm64: fall back to vmemmap_populate_basepages if not aligned with PMD

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Date:   Wed, 29 Jul 2020 11:34:24 +0800
From:   Jia He <justin.he@....com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Dave Jiang <dave.jiang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steve Capper <steve.capper@....com>,
        Mark Rutland <mark.rutland@....com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org,
        Wei Yang <richardw.yang@...ux.intel.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Ira Weiny <ira.weiny@...el.com>, Kaly Xin <Kaly.Xin@....com>,
        Jia He <justin.he@....com>
Subject: [RFC PATCH 6/6] arm64: fall back to vmemmap_populate_basepages if not aligned  with PMD_SIZE

In dax pmem kmem (dax pmem used as RAM device) case, the start address
might not be aligned with PMD_SIZE
e.g.
240000000-33fdfffff : Persistent Memory
  240000000-2421fffff : namespace0.0
  242400000-2bfffffff : dax0.0
    242400000-2bfffffff : System RAM (kmem)
pfn_to_page(0x242400000) is fffffe0007e90000.

Without this patch, vmemmap_populate(fffffe0007e90000, ...) will incorrectly
create a pmd mapping [fffffe0007e00000, fffffe0008000000] which contains
fffffe0007e90000.

This adds the check and then falls back to vmemmap_populate_basepages()

Signed-off-by: Jia He <justin.he@....com>
---
 arch/arm64/mm/mmu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index d69feb2cfb84..3b21bd47e801 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1102,6 +1102,10 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 
 	do {
 		next = pmd_addr_end(addr, end);
+		if (next - addr < PMD_SIZE) {
+			vmemmap_populate_basepages(start, next, node, altmap);
+			continue;
+		}
 
 		pgdp = vmemmap_pgd_populate(addr, node);
 		if (!pgdp)
-- 
2.17.1