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[PATCH v3 5/7] mm: replace vma->vm_flags indirect modification in ksm_madvise

Suren Baghdasaryan posted 7 patches 2 years, 7 months ago
There is a newer version of this series
[PATCH v3 5/7] mm: replace vma->vm_flags indirect modification in ksm_madvise
Posted by Suren Baghdasaryan 2 years, 7 months ago 
Replace indirect modifications to vma->vm_flags with calls to modifier
functions to be able to track flag changes and to keep vma locking
correctness.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
 arch/s390/mm/gmap.c                | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 1d67baa5557a..325a7a47d348 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -393,6 +393,7 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
 {
 	unsigned long gfn = memslot->base_gfn;
 	unsigned long end, start = gfn_to_hva(kvm, gfn);
+	unsigned long vm_flags;
 	int ret = 0;
 	struct vm_area_struct *vma;
 	int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
@@ -409,12 +410,14 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
 			ret = H_STATE;
 			break;
 		}
+		vm_flags = vma->vm_flags;
 		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-			  merge_flag, &vma->vm_flags);
+			  merge_flag, &vm_flags);
 		if (ret) {
 			ret = H_STATE;
 			break;
 		}
+		reset_vm_flags(vma, vm_flags);
 		start = vma->vm_end;
 	} while (end > vma->vm_end);
 
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 3a695b8a1e3c..d5eb47dcdacb 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2587,14 +2587,17 @@ int gmap_mark_unmergeable(void)
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
+	unsigned long vm_flags;
 	int ret;
 	VMA_ITERATOR(vmi, mm, 0);
 
 	for_each_vma(vmi, vma) {
+		vm_flags = vma->vm_flags;
 		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-				  MADV_UNMERGEABLE, &vma->vm_flags);
+				  MADV_UNMERGEABLE, &vm_flags);
 		if (ret)
 			return ret;
+		reset_vm_flags(vma, vm_flags);
 	}
 	mm->def_flags &= ~VM_MERGEABLE;
 	return 0;
-- 
2.39.1
Re: [PATCH v3 5/7] mm: replace vma->vm_flags indirect modification in ksm_madvise
Posted by Mel Gorman 2 years, 7 months ago 
On Wed, Jan 25, 2023 at 03:35:52PM -0800, Suren Baghdasaryan wrote:
> Replace indirect modifications to vma->vm_flags with calls to modifier
> functions to be able to track flag changes and to keep vma locking
> correctness.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> ---
>  arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
>  arch/s390/mm/gmap.c                | 5 ++++-
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index 1d67baa5557a..325a7a47d348 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -393,6 +393,7 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
>  {
>  	unsigned long gfn = memslot->base_gfn;
>  	unsigned long end, start = gfn_to_hva(kvm, gfn);
> +	unsigned long vm_flags;
>  	int ret = 0;
>  	struct vm_area_struct *vma;
>  	int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
> @@ -409,12 +410,14 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
>  			ret = H_STATE;
>  			break;
>  		}
> +		vm_flags = vma->vm_flags;
>  		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> -			  merge_flag, &vma->vm_flags);
> +			  merge_flag, &vm_flags);
>  		if (ret) {
>  			ret = H_STATE;
>  			break;
>  		}
> +		reset_vm_flags(vma, vm_flags);
>  		start = vma->vm_end;
>  	} while (end > vma->vm_end);

Add a comment on why the vm_flags are copied in case someone "optimises"
this in the future? Something like

/* Copy vm_flags to avoid any partial modifications in ksm_madvise. */

>  
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 3a695b8a1e3c..d5eb47dcdacb 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2587,14 +2587,17 @@ int gmap_mark_unmergeable(void)
>  {
>  	struct mm_struct *mm = current->mm;
>  	struct vm_area_struct *vma;
> +	unsigned long vm_flags;
>  	int ret;
>  	VMA_ITERATOR(vmi, mm, 0);
>  
>  	for_each_vma(vmi, vma) {
> +		vm_flags = vma->vm_flags;
>  		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> -				  MADV_UNMERGEABLE, &vma->vm_flags);
> +				  MADV_UNMERGEABLE, &vm_flags);
>  		if (ret)
>  			return ret;
> +		reset_vm_flags(vma, vm_flags);

Same.

Not necessary as such as there are few users of ksm_madvise and I doubt
it'll introduce new surprises.

With or without the comment;

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs
Re: [PATCH v3 5/7] mm: replace vma->vm_flags indirect modification in ksm_madvise
Posted by Suren Baghdasaryan 2 years, 7 months ago 
On Thu, Jan 26, 2023 at 7:19 AM Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Wed, Jan 25, 2023 at 03:35:52PM -0800, Suren Baghdasaryan wrote:
> > Replace indirect modifications to vma->vm_flags with calls to modifier
> > functions to be able to track flag changes and to keep vma locking
> > correctness.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > Acked-by: Michal Hocko <mhocko@suse.com>
> > ---
> >  arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
> >  arch/s390/mm/gmap.c                | 5 ++++-
> >  2 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> > index 1d67baa5557a..325a7a47d348 100644
> > --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> > +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> > @@ -393,6 +393,7 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
> >  {
> >       unsigned long gfn = memslot->base_gfn;
> >       unsigned long end, start = gfn_to_hva(kvm, gfn);
> > +     unsigned long vm_flags;
> >       int ret = 0;
> >       struct vm_area_struct *vma;
> >       int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
> > @@ -409,12 +410,14 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
> >                       ret = H_STATE;
> >                       break;
> >               }
> > +             vm_flags = vma->vm_flags;
> >               ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> > -                       merge_flag, &vma->vm_flags);
> > +                       merge_flag, &vm_flags);
> >               if (ret) {
> >                       ret = H_STATE;
> >                       break;
> >               }
> > +             reset_vm_flags(vma, vm_flags);
> >               start = vma->vm_end;
> >       } while (end > vma->vm_end);
>
> Add a comment on why the vm_flags are copied in case someone "optimises"
> this in the future? Something like
>
> /* Copy vm_flags to avoid any partial modifications in ksm_madvise. */

Ack.

>
> >
> > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> > index 3a695b8a1e3c..d5eb47dcdacb 100644
> > --- a/arch/s390/mm/gmap.c
> > +++ b/arch/s390/mm/gmap.c
> > @@ -2587,14 +2587,17 @@ int gmap_mark_unmergeable(void)
> >  {
> >       struct mm_struct *mm = current->mm;
> >       struct vm_area_struct *vma;
> > +     unsigned long vm_flags;
> >       int ret;
> >       VMA_ITERATOR(vmi, mm, 0);
> >
> >       for_each_vma(vmi, vma) {
> > +             vm_flags = vma->vm_flags;
> >               ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> > -                               MADV_UNMERGEABLE, &vma->vm_flags);
> > +                               MADV_UNMERGEABLE, &vm_flags);
> >               if (ret)
> >                       return ret;
> > +             reset_vm_flags(vma, vm_flags);
>
> Same.
>
> Not necessary as such as there are few users of ksm_madvise and I doubt
> it'll introduce new surprises.
>
> With or without the comment;
>
> Acked-by: Mel Gorman <mgorman@techsingularity.net>

Thanks!

>
> --
> Mel Gorman
> SUSE Labs

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