Re: [PATCH V5 2/3] riscv: Add ASID-based tlbflushing methods

Christoph Hellwig
2021-06-06T14:38:58Z

On Sun, Jun 06, 2021 at 09:03:58AM +0000, guoren@kernel.org wrote:
> +static inline void local_flush_tlb_all_asid(unsigned long asid)
> +{
> + __asm__ __volatile__ ("sfence.vma x0, %0"
> + :
> + : "r" (asid)
> + : "memory");
> +}
> +
> +static inline void local_flush_tlb_range_asid(unsigned long start,
> + unsigned long size, unsigned long asid)
> +{
> + unsigned long tmp, end = ALIGN(start + size, PAGE_SIZE);
> +
> + for (tmp = start & PAGE_MASK; tmp < end; tmp += PAGE_SIZE) {
> + __asm__ __volatile__ ("sfence.vma %0, %1"
> + :
> + : "r" (tmp), "r" (asid)
> + : "memory");
> + }

No need to expose these in a header.

> +static void __sbi_tlb_flush_range_asid(struct cpumask *cmask,
> + unsigned long start,
> + unsigned long size,
> + unsigned long asid)
> +{
> + struct cpumask hmask;
> + unsigned int cpuid;
> +
> + if (cpumask_empty(cmask))
> + return;
> +
> + cpuid = get_cpu();
> +
> + if (cpumask_any_but(cmask, cpuid) >= nr_cpu_ids) {
> + if (size == -1)
> + local_flush_tlb_all_asid(asid);
> + else
> + local_flush_tlb_range_asid(start, size, asid);
> + } else {
> + riscv_cpuid_to_hartid_mask(cmask, &hmask);
> + sbi_remote_sfence_vma_asid(cpumask_bits(&hmask),
> + start, size, asid);
> + }
> +
> + put_cpu();
> +}

Still no need to duplicate most of this logic. Also please document
why this uses a different tradeoff for the flush all logic compared
to the non-ASID path.

> +
> void flush_tlb_mm(struct mm_struct *mm)
> {
> - __sbi_tlb_flush_range(mm_cpumask(mm), 0, -1);
> + if (static_branch_unlikely(&use_asid_allocator))
> + __sbi_tlb_flush_range_asid(mm_cpumask(mm), 0, -1,
> + atomic_long_read(&mm->context.id));
> + else
> + __sbi_tlb_flush_range(mm_cpumask(mm), 0, -1);
> }
>
> void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)
> {
> - __sbi_tlb_flush_range(mm_cpumask(vma->vm_mm), addr, PAGE_SIZE);
> + if (static_branch_unlikely(&use_asid_allocator))
> + __sbi_tlb_flush_range_asid(mm_cpumask(vma->vm_mm), addr, PAGE_SIZE,
> + atomic_long_read(&vma->vm_mm->context.id));
> + else
> + __sbi_tlb_flush_range(mm_cpumask(vma->vm_mm), addr, PAGE_SIZE);
> }
>
> void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
> unsigned long end)
> {
> - __sbi_tlb_flush_range(mm_cpumask(vma->vm_mm), start, end - start);
> + if (static_branch_unlikely(&use_asid_allocator))
> + __sbi_tlb_flush_range_asid(mm_cpumask(vma->vm_mm), start, end - start,
> + atomic_long_read(&vma->vm_mm->context.id));
> + else
> + __sbi_tlb_flush_range(mm_cpumask(vma->vm_mm), start, end - start);

Various overly long lines (which are trivially avoided when doing the
right thing from the beginning).