linux-kernel - Re: [PATCH v12 05/31] mm: prepare for FAULT_FLAG

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Message-ID: <20190418220415.GE11645@redhat.com>
Date:   Thu, 18 Apr 2019 18:04:15 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Laurent Dufour <ldufour@...ux.ibm.com>
Cc:     akpm@...ux-foundation.org, mhocko@...nel.org, peterz@...radead.org,
        kirill@...temov.name, ak@...ux.intel.com, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        aneesh.kumar@...ux.ibm.com, benh@...nel.crashing.org,
        mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        sergey.senozhatsky.work@...il.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kemi.wang@...el.com, Daniel Jordan <daniel.m.jordan@...cle.com>,
        David Rientjes <rientjes@...gle.com>,
        Ganesh Mahendran <opensource.ganesh@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Punit Agrawal <punitagrawal@...il.com>,
        vinayak menon <vinayakm.list@...il.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        zhong jiang <zhongjiang@...wei.com>,
        Haiyan Song <haiyanx.song@...el.com>,
        Balbir Singh <bsingharora@...il.com>, sj38.park@...il.com,
        Michel Lespinasse <walken@...gle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, npiggin@...il.com,
        paulmck@...ux.vnet.ibm.com, Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v12 05/31] mm: prepare for FAULT_FLAG_SPECULATIVE

On Tue, Apr 16, 2019 at 03:44:56PM +0200, Laurent Dufour wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> When speculating faults (without holding mmap_sem) we need to validate
> that the vma against which we loaded pages is still valid when we're
> ready to install the new PTE.
> 
> Therefore, replace the pte_offset_map_lock() calls that (re)take the
> PTL with pte_map_lock() which can fail in case we find the VMA changed
> since we started the fault.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> [Port to 4.12 kernel]
> [Remove the comment about the fault_env structure which has been
>  implemented as the vm_fault structure in the kernel]
> [move pte_map_lock()'s definition upper in the file]
> [move the define of FAULT_FLAG_SPECULATIVE later in the series]
> [review error path in do_swap_page(), do_anonymous_page() and
>  wp_page_copy()]
> Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>

Reviewed-by: Jérôme Glisse <jglisse@...hat.com>

> ---
>  mm/memory.c | 87 +++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 58 insertions(+), 29 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index c6ddadd9d2b7..fc3698d13cb5 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2073,6 +2073,13 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
>  }
>  EXPORT_SYMBOL_GPL(apply_to_page_range);
>  
> +static inline bool pte_map_lock(struct vm_fault *vmf)

I am not fan of the name maybe pte_offset_map_lock_if_valid() ? But
that just a taste thing. So feel free to ignore this comment.


> +{
> +	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
> +				       vmf->address, &vmf->ptl);
> +	return true;
> +}
> +
>  /*
>   * handle_pte_fault chooses page fault handler according to an entry which was
>   * read non-atomically.  Before making any commitment, on those architectures