On Tue, Apr 2, 2019 at 2:05 PM Mike Rapoport <[email protected]> wrote: > > On Tue, Apr 02, 2019 at 06:02:38AM +0000, Anup Patel wrote: > > The Maximum Physical Memory 2GiB option for 64bit systems is currently > > broken because kernel hangs at boot-time when this option is enabled > > and the underlying system has more than 2GiB memory. > > > > This issue can be easily reproduced on SiFive Unleashed board where > > we have 8GiB of memory. > > > > This patch fixes above issue by reserving unusable memory region in > > setup_bootmem(). > > > > Signed-off-by: Anup Patel <[email protected]> > > --- > > arch/riscv/mm/init.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > > index 5fd8c922e1c2..6b063f20a9d0 100644 > > --- a/arch/riscv/mm/init.c > > +++ b/arch/riscv/mm/init.c > > @@ -121,6 +121,14 @@ void __init setup_bootmem(void) > > */ > > memblock_reserve(reg->base, vmlinux_end - reg->base); > > mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET); > > + > > + /* > > + * Reserve from the end of usable area to the end of > > + * region > > + */ > > + if ((reg->base + mem_size) < end) > > + memblock_reserve(reg->base + mem_size, > > + end - reg->base - mem_size); > > The memory above MAXPHYSMEM should not be reserved. It should be either > removed from memblock with memblock_remove or not added at the first place. > > Frankly, I fail to understand the logic behind setting PAGE_OFFSET to > MAXPHYSMEM and then using PAGE_OFFSET as the limit for accessible physical > memory. Still, as it is there, you can set MAX_MEMBLOCK_ADDR=PAGE_OFFSET in > arch/riscv/include/page.h and then early_init_dt_add_memory_arch() will > simply ignore the memory above PAGE_OFFSET.
Little explanation about current code ... The current code, assumes PAGE_OFFSET to have value such that upper-bits are 1s lower bits are 0s. For example, 0xc0000000 (32bit), 0xffffffff80000000 (64bit), and 0xffffffe000000000 (64bit) For above PAGE_OFFSET values, -PAGE_OFFSET is size of virtual address space and maximum supported physical memory is also -PAGE_OFFSET hence MAXPHYMEM is tied with -PAGE_OFFSET. If we try to force some arbitrary PAGE_OFFSET then things break. Regards, Anup
