From: Arnd Bergmann
[ Upstream commit cef397038167ac15d085914493d6c86385773709 ]
Stefan Agner reported a bug when using zsram on 32-bit Arm machines
with RAM above the 4GB address boundary:
Unable to handle kernel NULL pointer dereference at virtual address
pgd = a27bd01c
[] *pgd=236a0003, *pmd=1ffa64003
Internal error: Oops: 207 [#1] SMP ARM
Modules linked in: mdio_bcm_unimac(+) brcmfmac cfg80211 brcmutil
raspberrypi_hwmon hci_uart crc32_arm_ce bcm2711_thermal phy_generic genet
CPU: 0 PID: 123 Comm: mkfs.ext4 Not tainted 5.9.6 #1
Hardware name: BCM2711
PC is at zs_map_object+0x94/0x338
LR is at zram_bvec_rw.constprop.0+0x330/0xa64
pc : []lr : []psr: 6013
sp : e376bbe0 ip : fp : c1e2921c
r10: 0002 r9 : c1dda730 r8 :
r7 : e8ff7a00 r6 : r5 : 02f9ffa0 r4 : e371
r3 : 000fdffe r2 : c1e0ce80 r1 : ebf979a0 r0 :
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
Control: 30c5383d Table: 235c2a80 DAC: fffd
Process mkfs.ext4 (pid: 123, stack limit = 0x495a22e6)
Stack: (0xe376bbe0 to 0xe376c000)
As it turns out, zsram needs to know the maximum memory size, which
is defined in MAX_PHYSMEM_BITS when CONFIG_SPARSEMEM is set, or in
MAX_POSSIBLE_PHYSMEM_BITS on the x86 architecture.
The same problem will be hit on all 32-bit architectures that have a
physical address space larger than 4GB and happen to not enable sparsemem
and include asm/sparsemem.h from asm/pgtable.h.
After the initial discussion, I suggested just always defining
MAX_POSSIBLE_PHYSMEM_BITS whenever CONFIG_PHYS_ADDR_T_64BIT is
set, or provoking a build error otherwise. This addresses all
configurations that can currently have this runtime bug, but
leaves all other configurations unchanged.
I looked up the possible number of bits in source code and
datasheets, here is what I found:
- on ARC, CONFIG_ARC_HAS_PAE40 controls whether 32 or 40 bits are used
- on ARM, CONFIG_LPAE enables 40 bit addressing, without it we never
support more than 32 bits, even though supersections in theory allow
up to 40 bits as well.
- on MIPS, some MIPS32r1 or later chips support 36 bits, and MIPS32r5
XPA supports up to 60 bits in theory, but 40 bits are more than
anyone will ever ship
- On PowerPC, there are three different implementations of 36 bit
addressing, but 32-bit is used without CONFIG_PTE_64BIT
- On RISC-V, the normal page table format can support 34 bit
addressing. There is no highmem support on RISC-V, so anything
above 2GB is unused, but it might be useful to eventually support
CONFIG_ZRAM for high pages.
Fixes: 61989a80fb3a ("staging: zsmalloc: zsmalloc memory allocation library")
Fixes: 02390b87a945 ("mm/zsmalloc: Prepare to variable MAX_PHYSMEM_BITS")
Acked-by: Thomas Bogendoerfer
Reviewed-by: Stefan Agner
Tested-by: Stefan Agner
Acked-by: Mike Rapoport
Link:
https://lore.kernel.org/linux-mm/bdfa44bf1c570b05d6c70898e2bbb0acf234ecdf.1604762181.git.ste...@agner.ch/
Signed-off-by: Arnd Bergmann
Signed-off-by: Sasha Levin
[florian: patch arch/powerpc/include/asm/pte-common.h for 4.19.y]
Signed-off-by: Florian Fainelli
---
arch/arc/include/asm/pgtable.h| 2 ++
arch/arm/include/asm/pgtable-2level.h | 2 ++
arch/arm/include/asm/pgtable-3level.h | 2 ++
arch/mips/include/asm/pgtable-32.h| 3 +++
arch/powerpc/include/asm/pte-common.h | 2 ++
arch/riscv/include/asm/pgtable-32.h | 2 ++
include/asm-generic/pgtable.h | 13 +
7 files changed, 26 insertions(+)
diff --git a/arch/arc/include/asm/pgtable.h b/arch/arc/include/asm/pgtable.h
index cf4be70d5892..f231963b4011 100644
--- a/arch/arc/include/asm/pgtable.h
+++ b/arch/arc/include/asm/pgtable.h
@@ -138,8 +138,10 @@
#ifdef CONFIG_ARC_HAS_PAE40
#define PTE_BITS_NON_RWX_IN_PD1(0xff | PAGE_MASK |
_PAGE_CACHEABLE)
+#define MAX_POSSIBLE_PHYSMEM_BITS 40
#else
#define PTE_BITS_NON_RWX_IN_PD1(PAGE_MASK | _PAGE_CACHEABLE)
+#define MAX_POSSIBLE_PHYSMEM_BITS 32
#endif
/**
diff --git a/arch/arm/include/asm/pgtable-2level.h
b/arch/arm/include/asm/pgtable-2level.h
index 12659ce5c1f3..90bf19d99378 100644
--- a/arch/arm/include/asm/pgtable-2level.h
+++ b/arch/arm/include/asm/pgtable-2level.h
@@ -78,6 +78,8 @@
#define PTE_HWTABLE_OFF(PTE_HWTABLE_PTRS * sizeof(pte_t))
#define PTE_HWTABLE_SIZE (PTRS_PER_PTE * sizeof(u32))
+#define MAX_POSSIBLE_PHYSMEM_BITS 32
+
/*
* PMD_SHIFT determines the size of the area a second-level page table can map
* PGDIR_SHIFT determines what a third-level page table entry can map
diff --git a/arch/arm/include/asm/pgtable-3level.h
b/arch/arm/include/asm/pgtable-3level.h
index 6d50a11d7793..7ba08dd650e3 100644
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -37,6 +37,8 @@
#define PTE_HWTABLE_OFF