[v6 PATCH] riscv: mm: execute local TLB flush after populating vmemmap

[Alexandre Ghiti]

Hi Prabhakar,

On Tue, Jan 30, 2024 at 10:59 AM Lad, Prabhakar
<prabhakar.csengg at gmail.com> wrote:
>
> Hi Vincent,
>
> Thank you for the patch.
>
> On Wed, Jan 17, 2024 at 2:07 PM Vincent Chen <vincent.chen at sifive.com> wrote:
> >
> > The spare_init() calls memmap_populate() many times to create VA to PA
> > mapping for the VMEMMAP area, where all "struct page" are located once
> > CONFIG_SPARSEMEM_VMEMMAP is defined. These "struct page" are later
> > initialized in the zone_sizes_init() function. However, during this
> > process, no sfence.vma instruction is executed for this VMEMMAP area.
> > This omission may cause the hart to fail to perform page table walk
> > because some data related to the address translation is invisible to the
> > hart. To solve this issue, the local_flush_tlb_kernel_range() is called
> > right after the sparse_init() to execute a sfence.vma instruction for this
> > VMEMMAP area, ensuring that all data related to the address translation
> > is visible to the hart.
> >
> > Fixes: d95f1a542c3d ("RISC-V: Implement sparsemem")
> > Signed-off-by: Vincent Chen <vincent.chen at sifive.com>
> > Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>
> > ---
> >  arch/riscv/include/asm/tlbflush.h | 2 ++
> >  arch/riscv/mm/init.c              | 5 +++++
> >  arch/riscv/mm/tlbflush.c          | 6 ++++++
> >  3 files changed, 13 insertions(+)
> >
> I get below build issue with this patch applied:
>
> arch/riscv/mm/tlbflush.c:207:6: error: redefinition of
> 'local_flush_tlb_kernel_range'
>   207 | void local_flush_tlb_kernel_range(unsigned long start,
> unsigned long end)
>       |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> arch/riscv/mm/tlbflush.c:69:6: note: previous definition of
> 'local_flush_tlb_kernel_range' with type 'void(long unsigned int,
> long unsigned int)'
>    69 | void local_flush_tlb_kernel_range(unsigned long start,
> unsigned long end)
>       |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> make[4]: *** [scripts/Makefile.build:243: arch/riscv/mm/tlbflush.o] Error 1
> make[4]: *** Waiting for unfinished jobs....
>   CC      kernel/resource.o
> make[3]: *** [scripts/Makefile.build:481: arch/riscv/mm] Error 2
> make[3]: *** Waiting for unfinished jobs....
>
> I have attached the defconfig file.
>

Indeed, we recently added the same function, you can find a rebased
version of this patch on top of 6.8 here:
https://github.com/AlexGhiti/linux-riscv/commit/756d1871f58edac455773db0bb996f8d064a6b06

> Cheers,
> Prabhakar
>
> > diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
> > index 8f3418c5f172..525267379ccb 100644
> > --- a/arch/riscv/include/asm/tlbflush.h
> > +++ b/arch/riscv/include/asm/tlbflush.h
> > @@ -46,6 +46,7 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end);
> >  void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
> >                         unsigned long end);
> >  #endif
> > +void local_flush_tlb_kernel_range(unsigned long start, unsigned long end);
> >  #else /* CONFIG_SMP && CONFIG_MMU */
> >
> >  #define flush_tlb_all() local_flush_tlb_all()
> > @@ -66,6 +67,7 @@ static inline void flush_tlb_kernel_range(unsigned long start,
> >
> >  #define flush_tlb_mm(mm) flush_tlb_all()
> >  #define flush_tlb_mm_range(mm, start, end, page_size) flush_tlb_all()
> > +#define local_flush_tlb_kernel_range(start, end) flush_tlb_all()
> >  #endif /* !CONFIG_SMP || !CONFIG_MMU */
> >
> >  #endif /* _ASM_RISCV_TLBFLUSH_H */
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 2e011cbddf3a..cc56a0945120 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -1377,6 +1377,10 @@ void __init misc_mem_init(void)
> >         early_memtest(min_low_pfn << PAGE_SHIFT, max_low_pfn << PAGE_SHIFT);
> >         arch_numa_init();
> >         sparse_init();
> > +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> > +       /* The entire VMEMMAP region has been populated. Flush TLB for this region */
> > +       local_flush_tlb_kernel_range(VMEMMAP_START, VMEMMAP_END);
> > +#endif
> >         zone_sizes_init();
> >         arch_reserve_crashkernel();
> >         memblock_dump_all();
> > @@ -1386,6 +1390,7 @@ void __init misc_mem_init(void)
> >  int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
> >                                struct vmem_altmap *altmap)
> >  {
> > +       /* Defer the required TLB flush until the entire VMEMMAP region has been populated */
> >         return vmemmap_populate_basepages(start, end, node, NULL);
> >  }
> >  #endif
> > diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> > index e6659d7368b3..d11a4ae87ec1 100644
> > --- a/arch/riscv/mm/tlbflush.c
> > +++ b/arch/riscv/mm/tlbflush.c
> > @@ -193,6 +193,12 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> >         __flush_tlb_range(NULL, start, end - start, PAGE_SIZE);
> >  }
> >
> > +/* Flush a range of kernel pages without broadcasting */
> > +void local_flush_tlb_kernel_range(unsigned long start, unsigned long end)
> > +{
> > +       local_flush_tlb_range_asid(start, end - start, PAGE_SIZE, FLUSH_TLB_NO_ASID);
> > +}
> > +
> >  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >  void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
> >                         unsigned long end)
> > --
> > 2.34.1
> >
> >
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