linux-kernel - Re: [PATCH v1 4/5] KVM: s390: refactor and split some gmap helpers

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Message-ID: <20250521174137.5b2baaf6@p-imbrenda>
Date: Wed, 21 May 2025 17:41:37 +0200
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: Nina Schoetterl-Glausch <nsg@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, frankja@...ux.ibm.com,
        borntraeger@...ibm.com, seiden@...ux.ibm.com, nrb@...ux.ibm.com,
        david@...hat.com, hca@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v1 4/5] KVM: s390: refactor and split some gmap helpers

On Wed, 21 May 2025 17:30:00 +0200
Nina Schoetterl-Glausch <nsg@...ux.ibm.com> wrote:

> On Wed, 2025-05-21 at 17:19 +0200, Claudio Imbrenda wrote:
> > On Wed, 21 May 2025 16:55:18 +0200
> > Nina Schoetterl-Glausch <nsg@...ux.ibm.com> wrote:
> >   
> > > On Wed, 2025-05-14 at 18:38 +0200, Claudio Imbrenda wrote:  
> > > > Refactor some gmap functions; move the implementation into a separate
> > > > file with only helper functions. The new helper functions work on vm
> > > > addresses, leaving all gmap logic in the gmap functions, which mostly
> > > > become just wrappers.
> > > > 
> > > > The whole gmap handling is going to be moved inside KVM soon, but the
> > > > helper functions need to touch core mm functions, and thus need to
> > > > stay in the core of kernel.
> > > > 
> > > > Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> > > > ---
> > > >  MAINTAINERS                          |   2 +
> > > >  arch/s390/include/asm/gmap_helpers.h |  18 ++
> > > >  arch/s390/kvm/diag.c                 |  11 +-
> > > >  arch/s390/kvm/kvm-s390.c             |   3 +-
> > > >  arch/s390/mm/Makefile                |   2 +
> > > >  arch/s390/mm/gmap.c                  |  46 ++---
> > > >  arch/s390/mm/gmap_helpers.c          | 266 +++++++++++++++++++++++++++
> > > >  7 files changed, 307 insertions(+), 41 deletions(-)
> > > >  create mode 100644 arch/s390/include/asm/gmap_helpers.h
> > > >  create mode 100644 arch/s390/mm/gmap_helpers.c
> > > >     
> [...]
> 
> > > > +void __gmap_helper_zap_one(struct mm_struct *mm, unsigned long vmaddr)    
> > > 
> > > __gmap_helper_zap_mapping_pte ?  
> > 
> > but I'm not taking a pte as parameter  
> 
> The pte being zapped is the one mapping vmaddr, right?

I don't know, _pte kinda sounds to me as the function would be taking a
pte as parameter

> >   
> > >   
> > > > +{
> > > > +	struct vm_area_struct *vma;
> > > > +	spinlock_t *ptl;
> > > > +	pte_t *ptep;
> > > > +
> > > > +	mmap_assert_locked(mm);
> > > > +
> > > > +	/* Find the vm address for the guest address */
> > > > +	vma = vma_lookup(mm, vmaddr);
> > > > +	if (!vma || is_vm_hugetlb_page(vma))
> > > > +		return;
> > > > +
> > > > +	/* Get pointer to the page table entry */
> > > > +	ptep = get_locked_pte(mm, vmaddr, &ptl);
> > > > +	if (!likely(ptep))    
> > > 
> > > if (unlikely(!ptep)) reads nicer to me.  
> > 
> > ok
> >   
> > >   
> > > > +		return;
> > > > +	if (pte_swap(*ptep))
> > > > +		ptep_zap_swap_entry(mm, pte_to_swp_entry(*ptep));
> > > > +	pte_unmap_unlock(ptep, ptl);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(__gmap_helper_zap_one);    
> > > 
> > > Looks reasonable, but I'm not well versed enough in mm code to evaluate
> > > that with confidence.
> > >   
> > > > +
> > > > +void __gmap_helper_discard(struct mm_struct *mm, unsigned long vmaddr, unsigned long end)    
> > > 
> > > Maybe call this gmap_helper_discard_nolock or something.  
> > 
> > maybe __gmap_helper_discard_unlocked?
> > 
> > the __ prefix often implies lack of locking  
> 
> _nolock *definitely* implies it :P
> 
> [...]
> 
> > > 
> > > The stuff below is from arch/s390/mm/gmap.c right?
> > > Are you going to delete it from there?  
> > 
> > not in this series, but the next series will remove mm/gmap.c altogether  
> 
> Can't you do it with this one?

if you mean removing mm/gmap.c, no. I would need to push the whole gmap
rewrite series, which is not ready yet.

if you mean removing the redundant functions... I guess I could

> 
> 
> [...]