Re: [PATCH -v2 2/2] arm64, tlbflush: don't TLBI broadcast if page reused in write fault

["Huang, Ying" <ying.huang@linux.alibaba.com>]

Barry Song <21cnbao@gmail.com> writes:

> On Wed, Oct 22, 2025 at 10:46 PM Huang, Ying
> <ying.huang@linux.alibaba.com> wrote:
>
>> >
>> > I agree. Yet the ish barrier can still avoid the page faults during CPU0's PTL.
>>
>> IIUC, you think that dsb(ish) compared with dsb(nsh) can accelerate
>> memory writing (visible to other CPUs).  TBH, I suspect that this is the
>> case.
>
> Why? In any case, nsh is not a smp domain.

I think dsb(ish) will be slower than dsb(nsh) in theory.  I guess that
dsb just wait for the memory write to be visible in the specified
shareability domain instead of making write faster.

> I believe a dmb(ishst) is sufficient to ensure that the new PTE writes
> are visible

dmb(ishst) (smp_wmb()) should pair with dmb(ishld) (smp_rmb()).

> to other CPUs. I’m not quite sure why the current flush code uses dsb(ish);
> it seems like overkill.

dsb(ish) here is used for tlbi(XXis) broadcast.  It waits until the page
table change is visible to the page table walker of the remote CPU.

---
Best Regards,
Huang, Ying