[PATCH 2/4] RISC-V: Set current memblock limit

[Atish Patra]

On Sun, Jan 10, 2021 at 7:59 PM Anup Patel <anup at brainfault.org> wrote:
>
> On Thu, Jan 7, 2021 at 2:57 PM Atish Patra <atish.patra at wdc.com> wrote:
> >
> > Currently, linux kernel can not use last 4k bytes of addressable space because
> > IS_ERR_VALUE macro treats those as an error. This will be an issue for RV32
> > as any memblock allocator potentially allocate chunk of memory from the end
> > of DRAM (2GB) leading bad address error even though the address was technically
> > valid.
> >
> > Fix this issue by limiting the memblock if available memory spans the entire
> > address space.
> >
> > Signed-off-by: Atish Patra <atish.patra at wdc.com>
> > ---
> >  arch/riscv/mm/init.c | 16 ++++++++++++++--
> >  1 file changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index bf5379135e39..da53902ef0fc 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -157,9 +157,10 @@ static void __init setup_initrd(void)
> >  void __init setup_bootmem(void)
> >  {
> >         phys_addr_t mem_start = 0;
> > -       phys_addr_t start, end = 0;
> > +       phys_addr_t start, dram_end, end = 0;
> >         phys_addr_t vmlinux_end = __pa_symbol(&_end);
> >         phys_addr_t vmlinux_start = __pa_symbol(&_start);
> > +       phys_addr_t max_mapped_addr = __pa(PHYS_ADDR_MAX);
>
> Using PHYS_ADDR_MAX as the max virtual address does not look right.
>
> Better use __pa(~(ulong)0) here. Otherwise looks good to me.
>

ok will change it. Thanks for the review.

> Reviewed-by: Anup Patel <anup at brainfault.org>
>
> >         u64 i;
> >
> >         /* Find the memory region containing the kernel */
> > @@ -181,7 +182,18 @@ void __init setup_bootmem(void)
> >         /* Reserve from the start of the kernel to the end of the kernel */
> >         memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
> >
> > -       max_pfn = PFN_DOWN(memblock_end_of_DRAM());
> > +       dram_end = memblock_end_of_DRAM();
> > +
> > +       /*
> > +        * memblock allocator is not aware of the fact that last 4K bytes of
> > +        * the addressable memory can not be mapped because of IS_ERR_VALUE
> > +        * macro. Make sure that last 4k bytes are not usable by memblock
> > +        * if end of dram is equal to maximum addressable memory.
> > +        */
> > +       if (max_mapped_addr == (dram_end - 1))
> > +               memblock_set_current_limit(max_mapped_addr - 4096);
> > +
> > +       max_pfn = PFN_DOWN(dram_end);
> >         max_low_pfn = max_pfn;
> >         dma32_phys_limit = min(4UL * SZ_1G, (unsigned long)PFN_PHYS(max_low_pfn));
> >         set_max_mapnr(max_low_pfn);
> > --
> > 2.25.1
> >
> >
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>
> Regards,
> Anup
>
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-- 
Regards,
Atish