From 07464e88365e9236febaca9ed1a2e2006d8bc952 Mon Sep 17 00:00:00 2001
From: Oliver O'Halloran <oohall@gmail.com>
Date: Wed, 6 Feb 2019 13:04:53 +1100
Subject: [PATCH] libnvdimm: Fix altmap reservation size calculation

References: bsc#1127682
Patch-mainline: v5.1-rc1
Git-commit: 07464e88365e9236febaca9ed1a2e2006d8bc952

Libnvdimm reserves the first 8K of pfn and devicedax namespaces to
store a superblock describing the namespace. This 8K reservation
is contained within the altmap area which the kernel uses for the
vmemmap backing for the pages within the namespace. The altmap
allows for some pages at the start of the altmap area to be reserved
and that mechanism is used to protect the superblock from being
re-used as vmemmap backing.

The number of PFNs to reserve is calculated using:

	PHYS_PFN(SZ_8K)

Which is implemented as:

 #define PHYS_PFN(x) ((unsigned long)((x) >> PAGE_SHIFT))

So on systems where PAGE_SIZE is greater than 8K the reservation
size is truncated to zero and the superblock area is re-used as
vmemmap backing. As a result all the namespace information stored
in the superblock (i.e. if it's a PFN or DAX namespace) is lost
and the namespace needs to be re-created to get access to the
contents.

This patch fixes this by using PFN_UP() rather than PHYS_PFN() to ensure
that at least one page is reserved. On systems with a 4K pages size this
patch should have no effect.

Cc: stable@vger.kernel.org
Cc: Dan Williams <dan.j.williams@intel.com>
Fixes: ac515c084be9 ("libnvdimm, pmem, pfn: move pfn setup to the core")
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 drivers/nvdimm/pfn_devs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
index 040bbd9c367e..7760c1b91853 100644
--- a/drivers/nvdimm/pfn_devs.c
+++ b/drivers/nvdimm/pfn_devs.c
@@ -593,7 +593,7 @@ static unsigned long init_altmap_base(resource_size_t base)
 
 static unsigned long init_altmap_reserve(resource_size_t base)
 {
-	unsigned long reserve = PHYS_PFN(SZ_8K);
+	unsigned long reserve = PFN_UP(SZ_8K);
 	unsigned long base_pfn = PHYS_PFN(base);
 
 	reserve += base_pfn - PFN_SECTION_ALIGN_DOWN(base_pfn);
-- 
2.20.1