Re: [PATCH] RISC-V-fixes: relocate DTB if it's outside memory region

[Palmer Dabbelt]

On Thu, 24 Mar 2022 02:37:29 PDT (-0700), Conor.Dooley@xxxxxxxxxxxxx wrote:
> On 22/03/2022 13:28, Nick Kossifidis wrote:
> > In case the DTB provided by the bootloader/BootROM is before the kernel
> > image or outside /memory, we won't be able to access it through the
> > linear mapping, and get a segfault on setup_arch(). Currently OpenSBI
> > relocates DTB but that's not always the case (e.g. if FW_JUMP_FDT_ADDR
> > is not specified), and it's also not the most portable approach since
> > the default FW_JUMP_FDT_ADDR of the generic platform relocates the DTB
> > at a specific offset that may not be available. To avoid this situation
> > copy DTB so that it's visible through the linear mapping.
> >
> > Signed-off-by: Nick Kossifidis <mick@xxxxxxxxxxxx>
>
> Albeit in a backport, I tested this on a PolarFire SoC based board.
> So I guess, Tested-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>

My scripts don't pick these up unless they're on their own line, not 
sure if that's too conservative but it's on purpose.  I just sort of 
stumbled into this one so it's in.

> And a lot cleaner than using create_pgd_mapping in setup_vm_final to do it :)
>
> Thanks,
> Conor.
>
> > ---
> >   arch/riscv/mm/init.c | 21 +++++++++++++++++++--
> >   1 file changed, 19 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 0d588032d..697a9aed4 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -206,8 +206,25 @@ static void __init setup_bootmem(void)
> >   	 * early_init_fdt_reserve_self() since __pa() does
> >   	 * not work for DTB pointers that are fixmap addresses
> >   	 */
> > -	if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
> > -		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> > +	if (!IS_ENABLED(CONFIG_BUILTIN_DTB)) {
> > +		/*
> > +		 * In case the DTB is not located in a memory region we won't
> > +		 * be able to locate it later on via the linear mapping and
> > +		 * get a segfault when accessing it via __va(dtb_early_pa).
> > +		 * To avoid this situation copy DTB to a memory region.
> > +		 * Note that memblock_phys_alloc will also reserve DTB region.
> > +		 */
> > +		if (!memblock_is_memory(dtb_early_pa)) {
> > +			size_t fdt_size = fdt_totalsize(dtb_early_va);
> > +			phys_addr_t new_dtb_early_pa = memblock_phys_alloc(fdt_size, PAGE_SIZE);
> > +			void *new_dtb_early_va = early_memremap(new_dtb_early_pa, fdt_size);
> > +
> > +			memcpy(new_dtb_early_va, dtb_early_va, fdt_size);
> > +			early_memunmap(new_dtb_early_va, fdt_size);
> > +			_dtb_early_pa = new_dtb_early_pa;
> > +		} else
> > +			memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> > +	}
> >   
> >   	early_init_fdt_scan_reserved_mem();
> >   	dma_contiguous_reserve(dma32_phys_limit);