linux-kernel - Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

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Date:   Wed, 25 Jan 2023 16:01:05 +0000
From:   Liam Merwick <liam.merwick@...cle.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>, tabba@...gle.com,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com, Liam Merwick <liam.merwick@...cle.com>
Subject: Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM

On 25/01/2023 12:53, Kirill A. Shutemov wrote:
> On Wed, Jan 25, 2023 at 12:20:26AM +0000, Sean Christopherson wrote:
>> On Tue, Jan 24, 2023, Liam Merwick wrote:
>>> On 14/01/2023 00:37, Sean Christopherson wrote:
>>>> On Fri, Dec 02, 2022, Chao Peng wrote:
...
>>>
>>> When running LTP (https://github.com/linux-test-project/ltp) on the v10
>>> bits (and also with Sean's branch above) I encounter the following NULL
>>> pointer dereference with testcases/kernel/syscalls/madvise/madvise01
>>> (100% reproducible).
>>>
>>> It appears that in restrictedmem_error_page() inode->i_mapping->private_data
>>> is NULL
>>> in the list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list)
>>> but I don't know why.
>>
>> Kirill, can you take a look?  Or pass the buck to someone who can? :-)
> 
> The patch below should help.

Thanks, this works for me.

Regards,
Liam

> 
> diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
> index 15c52301eeb9..39ada985c7c0 100644
> --- a/mm/restrictedmem.c
> +++ b/mm/restrictedmem.c
> @@ -307,14 +307,29 @@ void restrictedmem_error_page(struct page *page, struct address_space *mapping)
>   
>   	spin_lock(&sb->s_inode_list_lock);
>   	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> -		struct restrictedmem *rm = inode->i_mapping->private_data;
>   		struct restrictedmem_notifier *notifier;
> -		struct file *memfd = rm->memfd;
> +		struct restrictedmem *rm;
>   		unsigned long index;
> +		struct file *memfd;
>   
> -		if (memfd->f_mapping != mapping)
> +		if (atomic_read(&inode->i_count))
>   			continue;
>   
> +		spin_lock(&inode->i_lock);
> +		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
> +			spin_unlock(&inode->i_lock);
> +			continue;
> +		}
> +
> +		rm = inode->i_mapping->private_data;
> +		memfd = rm->memfd;
> +
> +		if (memfd->f_mapping != mapping) {
> +			spin_unlock(&inode->i_lock);
> +			continue;
> +		}
> +		spin_unlock(&inode->i_lock);
> +
>   		xa_for_each_range(&rm->bindings, index, notifier, start, end)
>   			notifier->ops->error(notifier, start, end);
>   		break;