Re: [PATCH] mm: hugetlb: fix HVO crash on s390

[Luiz Capitulino <luizcap@redhat.com>]

On 2025-10-28 15:37, Heiko Carstens wrote:
> On Tue, Oct 28, 2025 at 01:15:57PM -0400, Luiz Capitulino wrote:
>>>> flush_tlb_all() however is the *closest* equivalent to this that's behind an
>>>> arch generic API i.e. flushing kernel address space on all CPUs TLBs. IIUC, x86
>>>> when doing flush_tlb_kernel_range with enough pages it switches to flush_tlb_all
>>>> (these days on modern AMDs it's even one instruction solely in the calling CPU).
>>>
>>> Considering that flush_tlb_all() should be mapped to __tlb_flush_global()
>>> and not __tlb_flush_kernel() on s390.
>>
>> You're right.
>>
>>> However if there is only a need to flush tlb entries for the complete(?)
>>> kernel address space, then I'd rather propose a new tlb_flush_kernel()
>>> instead of a big hammer. If I'm not mistaken flush_tlb_kernel_range()
>>> exists for just avoiding that. And if architectures can avoid a global
>>> flush of _all_ tlb entries then that should be made possible.
>>
>> Should we take a v2 doing your suggestion above for now and work on
>> the tlb_flush_kernel() idea as a follow up improvement? At least we
>> go from crashing to flushing more than we should...
> 
> That's of course fine. I guess for stable backports a small fix is the
> best way forward anyway.

Exactly. I'll also see if I can find time to explore your API
improvement suggestion. I'll send v2 shortly.