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Message-ID: <CAJ+HfNhYb9wNJ5m7-VEo1=FdRJ_h4fBYm2YqS+q=T6xrth2sSA@mail.gmail.com>
Date: Mon, 9 Dec 2024 12:31:10 +0100
From: Björn Töpel <bjorn.topel@...il.com>
To: Xu Lu <luxu.kernel@...edance.com>
Cc: paul.walmsley@...ive.com, palmer@...belt.com, alexghiti@...osinc.com,
bjorn@...osinc.com, lihangjing@...edance.com, xieyongji@...edance.com,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH v3] riscv: mm: Fix the out of bound issue
of vmemmap address
Hi,
On Mon, 9 Dec 2024 at 12:25, Xu Lu <luxu.kernel@...edance.com> wrote:
>
> Hi Björn,
>
> Thanks for your comment. Is it OK to introduce the new and unused
> variable 'vmemmap_start_pfn' when CONFIG_SPARSEMEM_VMEMMAP is
> disabled?
The declaration, yes. Definition, no!
Cheers,
Björn
> On Mon, Dec 9, 2024 at 7:03 PM Björn Töpel <bjorn@...nel.org> wrote:
> >
> > 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
>
> Best Regards,
>
> Xu Lu
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