Re: [RFC 11/20] mm/tlb: remove arch-specific tlb_start/end_vma()

Nadav Amit
2021-02-02T09:56:22Z

> On Feb 2, 2021, at 1:31 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Feb 02, 2021 at 07:20:55AM +0000, Nadav Amit wrote:
>> Arm does not define tlb_end_vma, and consequently it flushes the TLB after
>> each VMA. I suspect it is not intentional.
>
> ARM is one of those that look at the VM_EXEC bit to explicitly flush
> ITLB IIRC, so it has to.

Hmm… I don’t think Arm is doing that. At least arm64 does not use the
default tlb_flush(), and it does not seem to consider VM_EXEC (at least in
this path):

static inline void tlb_flush(struct mmu_gather *tlb)
{
struct vm_area_struct vma = TLB_FLUSH_VMA(tlb->mm, 0);
bool last_level = !tlb->freed_tables;
unsigned long stride = tlb_get_unmap_size(tlb);
int tlb_level = tlb_get_level(tlb);

/*
* If we're tearing down the address space then we only care about
* invalidating the walk-cache, since the ASID allocator won't
* reallocate our ASID without invalidating the entire TLB.
*/
if (tlb->mm_exiting) {
if (!last_level)
flush_tlb_mm(tlb->mm);
return;
}

__flush_tlb_range(&vma, tlb->start, tlb->end, stride,
last_level, tlb_level);
}