linux-kernel - Re: [PATCH] arm64: Change elfcore for_each_mte

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Date:   Tue, 22 Feb 2022 16:20:16 +0000
From:   Will Deacon <will@...nel.org>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: [PATCH] arm64: Change elfcore for_each_mte_vma() to use VMA
 iterator

On Tue, Feb 22, 2022 at 02:26:03PM +0000, Liam Howlett wrote:
> * Catalin Marinas <catalin.marinas@....com> [220221 13:07]:
> > On Fri, Feb 18, 2022 at 02:37:04AM +0000, Liam Howlett wrote:
> > > diff --git a/arch/arm64/kernel/elfcore.c b/arch/arm64/kernel/elfcore.c
> > > index 3455ee4acc04..930a0bc4cac4 100644
> > > --- a/arch/arm64/kernel/elfcore.c
> > > +++ b/arch/arm64/kernel/elfcore.c
> > > @@ -8,9 +8,9 @@
> > >  #include <asm/cpufeature.h>
> > >  #include <asm/mte.h>
> > >  
> > > -#define for_each_mte_vma(tsk, vma)					\
> > > +#define for_each_mte_vma(vmi, vma)					\
> > >  	if (system_supports_mte())					\
> > > -		for (vma = tsk->mm->mmap; vma; vma = vma->vm_next)	\
> > > +		for_each_vma(vmi, vma)					\
> > >  			if (vma->vm_flags & VM_MTE)
> > >  
> > >  static unsigned long mte_vma_tag_dump_size(struct vm_area_struct *vma)
> > > @@ -65,8 +65,9 @@ Elf_Half elf_core_extra_phdrs(void)
> > >  {
> > >  	struct vm_area_struct *vma;
> > >  	int vma_count = 0;
> > > +	VMA_ITERATOR(vmi, current->mm, 0);
> > >  
> > > -	for_each_mte_vma(current, vma)
> > > +	for_each_mte_vma(vmi, vma)
> > >  		vma_count++;
> > 
> > I'm fine with the patch but it can't be applied to arm64 for-next/mte
> > branch as it won't build and the maple tree doesn't have the MTE
> > patches. Do you have a stable branch with the for_each_vma() iterator?
> 
> The vma iterator uses the maple tree, so this patch would resolve the
> conflict but both branches are needed.

I'm not really sure what to do here, then. I think the conflict is nasty
enough that we should resolve it before the trees reach Linus, but there
doesn't seem to be a way forward other than one of us merging the other
branch. I'd like to avoid having MTE coredump support depend on the maple
tree work.

Is there some way you could provide a branch which implements
for_each_vma() using the old vma list, and then the maple tree series
could switch that over to the maple tree without breaking things?

Will