linux-kernel - Re: [PATCH 3/3] riscv: Make sure the kernel mapping does not overlap with IS_ERR

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Message-ID: <mhng-bc552805-71aa-4a1e-afa7-dfd08cfba35b@palmerdabbelt-glaptop>
Date:   Fri, 23 Jul 2021 17:58:08 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     alex@...ti.fr
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        wangkefeng.wang@...wei.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, alex@...ti.fr
Subject:     Re: [PATCH 3/3] riscv: Make sure the kernel mapping does not overlap with IS_ERR_VALUE

On Tue, 29 Jun 2021 02:13:48 PDT (-0700), alex@...ti.fr wrote:
> The check that is done in setup_bootmem currently only works for 32-bit
> kernel since the kernel mapping has been moved outside of the linear
> mapping for 64-bit kernel. So make sure that for 64-bit kernel, the kernel
> mapping does not overlap with the last 4K of the addressable memory.
>
> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
> ---
>  arch/riscv/mm/init.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index a1a0c4afa80f..a90c41bc9485 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -156,7 +156,7 @@ static void __init setup_bootmem(void)
>  {
>  	phys_addr_t vmlinux_end = __pa_symbol(&_end);
>  	phys_addr_t vmlinux_start = __pa_symbol(&_start);
> -	phys_addr_t max_mapped_addr = __pa(~(ulong)0);
> +	phys_addr_t __maybe_unused max_mapped_addr;
>  	phys_addr_t dram_end;
>
>  #ifdef CONFIG_XIP_KERNEL
> @@ -179,14 +179,20 @@ static void __init setup_bootmem(void)
>  	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
>
>  	dram_end = memblock_end_of_DRAM();
> +#ifndef CONFIG_64BIT
>  	/*
>  	 * 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 end of dram is equal to maximum addressable memory. For 64-bit
> +	 * kernel, this problem can't happen here as the end of the virtual
> +	 * address space is occupied by the kernel mapping then this check must
> +	 * be done in create_kernel_page_table.
>  	 */
> +	max_mapped_addr = __pa(~(ulong)0);
>  	if (max_mapped_addr == (dram_end - 1))
>  		memblock_set_current_limit(max_mapped_addr - 4096);
> +#endif
>
>  	min_low_pfn = PFN_UP(memblock_start_of_DRAM());
>  	max_low_pfn = max_pfn = PFN_DOWN(dram_end);
> @@ -556,6 +562,7 @@ static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size,
>  	uintptr_t va, end_va;
>
>  	end_va = kernel_virt_addr + load_sz;
> +
>  	for (va = kernel_virt_addr; va < end_va; va += map_size)
>  		create_pgd_mapping(pgdir, va,
>  				   load_pa + (va - kernel_virt_addr),
> @@ -602,6 +609,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	/* Sanity check alignment and size */
>  	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
>  	BUG_ON((load_pa % map_size) != 0);
> +#ifdef CONFIG_64BIT
> +	/*
> +	 * The last 4K bytes of the addressable memory can not be mapped because
> +	 * of IS_ERR_VALUE macro.
> +	 */
> +	BUG_ON((kernel_virt_addr + load_sz) > ADDRESS_SPACE_END - SZ_4K);
> +#endif
>
>  	pt_ops.alloc_pte = alloc_pte_early;
>  	pt_ops.get_pte_virt = get_pte_virt_early;

Thanks.  These are on fixes, with some fixes tags added.  This one had 
some merge conflicts that I had to fix up, LMK if something went wrong.