Re: [PATCH v13 57/70] mm/mlock: use vma iterator and maple state instead of vma linked list

[Liam Howlett <liam.howlett@oracle.com>]

* Mark Brown <broonie@kernel.org> [220824 20:34]:
> On Mon, Aug 22, 2022 at 03:06:30PM +0000, Liam Howlett wrote:
> > From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> > 
> > Handle overflow checking in count_mm_mlocked_page_nr() differently.
> 
> Our QA team found that since next-20220823 we're seeing a couple of test
> failures in the check_mmap_options kselftest on arm64 platforms with MTE
> that aren't present in mainline:
> 
> # # FAIL: mprotect not ignoring clear PROT_MTE property
> # not ok 21 Check clear PROT_MTE flags with private mapping, sync error mode and mmap memory
> # # FAIL: mprotect not ignoring clear PROT_MTE property
> # not ok 22 Check clear PROT_MTE flags with private mapping and sync error mode and mmap/mprotect memory

Thanks.

> 
> I bisected this using qemu[1] which landed on 4ceb4bca479d41a
> ("mm/mprotect: use maple tree navigation instead of vma linked list"),
> though I'm not 100% sure I trust the specific identification of the
> commit I'm pretty confident it's at the very least in this series.  I've
> not done any analysis of the failure beyond getting this bisect result.
> 
> [1] qemu -smp cpus=4 -cpu max -machine virt,gic-version=3,mte=on

This helps a lot.  I think your bisect is accurate:

...
        struct mmu_gather tlb;
+       MA_STATE(mas, &current->mm->mm_mt, start, start);
 
        start = untagged_addr(start);
...

It looks like I search against the tagged address.  I should initialize
the state to 0 and mas_set(&mas, start) after untagging the address.

I'll send out a patch once I have recreated and verified this is the
issue.

Cheers,
Liam
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