linux-kernel - Re: [PATCH v3] riscv: mm: Fix the out of bound issue of vmemmap address

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Message-ID: <87v7vtw234.fsf@all.your.base.are.belong.to.us>
Date: Mon, 09 Dec 2024 12:03:11 +0100
From: Björn Töpel <bjorn@...nel.org>
To: Xu Lu <luxu.kernel@...edance.com>, paul.walmsley@...ive.com,
 palmer@...belt.com, alexghiti@...osinc.com, bjorn@...osinc.com
Cc: lihangjing@...edance.com, xieyongji@...edance.com,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, Xu Lu
 <luxu.kernel@...edance.com>
Subject: Re: [PATCH v3] riscv: mm: Fix the out of bound issue of vmemmap
 address

Minor nits below; Too many ifdefs.

Xu Lu <luxu.kernel@...edance.com> writes:

> In sparse vmemmap model, the virtual address of vmemmap is calculated as:
> ((struct page *)VMEMMAP_START - (phys_ram_base >> PAGE_SHIFT)).
> And the struct page's va can be calculated with an offset:
> (vmemmap + (pfn)).
>
> However, when initializing struct pages, kernel actually starts from the
> first page from the same section that phys_ram_base belongs to. If the
> first page's physical address is not (phys_ram_base >> PAGE_SHIFT), then
> we get an va below VMEMMAP_START when calculating va for it's struct page.
>
> For example, if phys_ram_base starts from 0x82000000 with pfn 0x82000, the
> first page in the same section is actually pfn 0x80000. During
> init_unavailable_range(), we will initialize struct page for pfn 0x80000
> with virtual address ((struct page *)VMEMMAP_START - 0x2000), which is
> below VMEMMAP_START as well as PCI_IO_END.
>
> This commit fixes this bug by introducing a new variable
> 'vmemmap_start_pfn' which is aligned with memory section size and using
> it to calculate vmemmap address instead of phys_ram_base.
>
> Fixes: a11dd49dcb93 ("riscv: Sparse-Memory/vmemmap out-of-bounds fix")
> Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
> ---
>  arch/riscv/include/asm/page.h    |  4 ++++
>  arch/riscv/include/asm/pgtable.h |  4 +++-
>  arch/riscv/mm/init.c             | 18 ++++++++++++++++++
>  3 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 71aabc5c6713..a1be1adcfb85 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -123,6 +123,10 @@ struct kernel_mapping {
>  extern struct kernel_mapping kernel_map;
>  extern phys_addr_t phys_ram_base;
>  
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP

Not needed, and should be removed.

> +extern unsigned long vmemmap_start_pfn;
> +#endif
> +
>  #define is_kernel_mapping(x)	\
>  	((x) >= kernel_map.virt_addr && (x) < (kernel_map.virt_addr + kernel_map.size))
>  
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index d4e99eef90ac..e2dbd4b9a686 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -87,7 +87,9 @@
>   * Define vmemmap for pfn_to_page & page_to_pfn calls. Needed if kernel
>   * is configured with CONFIG_SPARSEMEM_VMEMMAP enabled.
>   */
> -#define vmemmap		((struct page *)VMEMMAP_START - (phys_ram_base >> PAGE_SHIFT))
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP

Dito, please remove.

> +#define vmemmap		((struct page *)VMEMMAP_START - vmemmap_start_pfn)
> +#endif
>  
>  #define PCI_IO_SIZE      SZ_16M
>  #define PCI_IO_END       VMEMMAP_START
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 0e8c20adcd98..e7c52d647f50 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -32,6 +32,9 @@
>  #include <asm/numa.h>
>  #include <asm/pgtable.h>
>  #include <asm/sections.h>
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP

Not needed, please remove.

> +#include <asm/sparsemem.h>
> +#endif
>  #include <asm/soc.h>
>  #include <asm/tlbflush.h>
>  
> @@ -62,6 +65,13 @@ EXPORT_SYMBOL(pgtable_l5_enabled);
>  phys_addr_t phys_ram_base __ro_after_init;
>  EXPORT_SYMBOL(phys_ram_base);
>  
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> +#define VMEMMAP_ADDR_ALIGN	(1ULL << SECTION_SIZE_BITS)
> +
> +unsigned long vmemmap_start_pfn __ro_after_init;
> +EXPORT_SYMBOL(vmemmap_start_pfn);
> +#endif
> +
>  unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
>  							__page_aligned_bss;
>  EXPORT_SYMBOL(empty_zero_page);
> @@ -243,6 +253,11 @@ static void __init setup_bootmem(void)
>  	if (!IS_ENABLED(CONFIG_XIP_KERNEL))
>  		phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
>  
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> +	if (!IS_ENABLED(CONFIG_XIP_KERNEL))
> +		vmemmap_start_pfn = round_down(phys_ram_base, VMEMMAP_ADDR_ALIGN) >> PAGE_SHIFT;
> +#endif
> +

Please fold this into the if-statement above, e.g.:
  |         if (!IS_ENABLED(CONFIG_XIP_KERNEL)) {
  |                 phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
  | #if defined(CONFIG_SPARSEMEM_VMEMMAP)
  |                 vmemmap_start_pfn = round_down(phys_ram_base, VMEMMAP_ADDR_ALIGN) >> PAGE_SHIFT;
  | #endif
  |         }


Björn