linux-kernel - Re: [PATCH v3 14/16] mm/mmap: Use PHYS_PFN in mmap

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Message-ID: <7ifrcfw35jqp5zlu2zofzexiy7kw5o5pwqxrolfk4azwpv4w24@uhw2ksxdswkm>
Date: Tue, 9 Jul 2024 14:35:16 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Lorenzo Stoakes <lstoakes@...il.com>,
        Matthew Wilcox <willy@...radead.org>, sidhartha.kumar@...cle.com,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Bert Karwatzki <spasswolf@....de>, Jiri Olsa <olsajiri@...il.com>,
        linux-kernel@...r.kernel.org, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v3 14/16] mm/mmap: Use PHYS_PFN in mmap_region()

* Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [240708 08:21]:
> On Thu, Jul 04, 2024 at 02:27:16PM GMT, Liam R. Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> >
> > Instead of shifting the length by PAGE_SIZE, use PHYS_PFN.  Also use the
> > existing local variable everywhere instead of some of the time.
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > ---
> >  mm/mmap.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 0c334eeae8cd..b14da6bd257f 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2935,7 +2935,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >  	struct mm_struct *mm = current->mm;
> >  	struct vm_area_struct *vma = NULL;
> >  	struct vm_area_struct *next, *prev, *merge;
> > -	pgoff_t pglen = len >> PAGE_SHIFT;
> > +	pgoff_t pglen = PHYS_PFN(len);
> >  	unsigned long charged = 0;
> >  	struct vma_munmap_struct vms;
> >  	struct ma_state mas_detach;
> > @@ -2955,7 +2955,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >  	 * MAP_FIXED may remove pages of mappings that intersects with requested
> >  	 * mapping. Account for the pages it would unmap.
> >  	 */
> > -	if (!may_expand_vm(mm, vm_flags, (len >> PAGE_SHIFT) - nr_pages))
> > +	if (!may_expand_vm(mm, vm_flags, pglen - nr_pages))
> >  		return -ENOMEM;
> >
> >  	if (unlikely(!can_modify_mm(mm, addr, end)))
> > @@ -2990,7 +2990,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >  	 * Private writable mapping: check memory availability
> >  	 */
> >  	if (accountable_mapping(file, vm_flags)) {
> > -		charged = len >> PAGE_SHIFT;
> > +		charged = pglen;
> >  		charged -= nr_accounted;
> >  		if (security_vm_enough_memory_mm(mm, charged))
> >  			goto abort_munmap;
> > @@ -3149,14 +3149,14 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> >  	if (vms.nr_pages)
> >  		vms_complete_munmap_vmas(&vms, &mas_detach);
> >
> > -	vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
> > +	vm_stat_account(mm, vm_flags, pglen);
> >  	if (vm_flags & VM_LOCKED) {
> >  		if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
> >  					is_vm_hugetlb_page(vma) ||
> >  					vma == get_gate_vma(current->mm))
> >  			vm_flags_clear(vma, VM_LOCKED_MASK);
> >  		else
> > -			mm->locked_vm += (len >> PAGE_SHIFT);
> > +			mm->locked_vm += pglen;
> >  	}
> >
> >  	if (file)
> > --
> > 2.43.0
> >
> 
> Maybe I should literally look ahead before making comments :)) thanks for
> reading my mind and doing what I asked though! ;)
> 
> However I don't think you've fixed the duplication of PHYS_PFN(vm_end -
> vm_start) in count_vma_pages_range() - still worth doing I think.

I drop that function in the last patch so probably not worth doing.
This is just a few patches before the axe drops.

> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>