[PATCH v3] riscv: mm: execute local TLB flush after populating vmemmap

[Palmer Dabbelt]

On Sun, 16 Apr 2023 23:06:18 PDT (-0700), 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 spare_init() to execute a sfence.vma instruction for the
> 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>
> Reviewed-by: Andrew Jones <ajones at ventanamicro.com>
> ---
>  arch/riscv/include/asm/tlbflush.h | 7 +++++++
>  arch/riscv/mm/init.c              | 5 +++++
>  2 files changed, 12 insertions(+)
>
> diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
> index a09196f8de68..f9d3712bd93b 100644
> --- a/arch/riscv/include/asm/tlbflush.h
> +++ b/arch/riscv/include/asm/tlbflush.h
> @@ -61,4 +61,11 @@ static inline void flush_tlb_kernel_range(unsigned long start,
>  	flush_tlb_all();
>  }
>
> +/* Flush a range of kernel pages without broadcasting */
> +static inline void local_flush_tlb_kernel_range(unsigned long start,
> +						unsigned long end)
> +{
> +	local_flush_tlb_all();

Why is this a global flush, istead of a range-based one?  We should 
probably make the same change for flush_tlb_kernel_range(), though 
that's not a fix.

> +}
> +
>  #endif /* _ASM_RISCV_TLBFLUSH_H */
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 0f14f4a8d179..bcf365cbbcc1 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -1221,6 +1221,10 @@ 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();
>  	reserve_crashkernel();
>  	memblock_dump_all();
> @@ -1230,6 +1234,7 @@ 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