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

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Message-ID: <20251028193708.7213A7e-hca@linux.ibm.com>
Date: Tue, 28 Oct 2025 20:37:08 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Luiz Capitulino <luizcap@...hat.com>
Cc: Joao Martins <joao.m.martins@...cle.com>, osalvador@...e.de,
        akpm@...ux-foundation.org, david@...hat.com, aneesh.kumar@...nel.org,
        borntraeger@...ux.ibm.com, mike.kravetz@...cle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, Vasily Gorbik <gor@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [PATCH] mm: hugetlb: fix HVO crash on s390

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.