linux-kernel - Re: [PATCH v2] KVM: x86: Check for rmaps allocation

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Date:   Fri, 7 Jan 2022 18:03:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Peter Xu <peterx@...hat.com>
Cc:     Nikunj A Dadhania <nikunj@....com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, vasant.hegde@....com,
        brijesh.singh@....com
Subject: Re: [PATCH v2] KVM: x86: Check for rmaps allocation

On 1/7/22 18:01, Sean Christopherson wrote:
> On Wed, Jan 05, 2022, Peter Xu wrote:
>> On Wed, Jan 05, 2022 at 09:33:37AM +0530, Nikunj A Dadhania wrote:
>>> With TDP MMU being the default now, access to mmu_rmaps_stat debugfs
>>> file causes following oops:
>>>
>>> BUG: kernel NULL pointer dereference, address: 0000000000000000
>>> PGD 0 P4D 0
>>> Oops: 0000 [#1] PREEMPT SMP NOPTI
>>> CPU: 7 PID: 3185 Comm: cat Not tainted 5.16.0-rc4+ #204
>>> RIP: 0010:pte_list_count+0x6/0x40
>>>   Call Trace:
>>>    <TASK>
>>>    ? kvm_mmu_rmaps_stat_show+0x15e/0x320
>>>    seq_read_iter+0x126/0x4b0
>>>    ? aa_file_perm+0x124/0x490
>>>    seq_read+0xf5/0x140
>>>    full_proxy_read+0x5c/0x80
>>>    vfs_read+0x9f/0x1a0
>>>    ksys_read+0x67/0xe0
>>>    __x64_sys_read+0x19/0x20
>>>    do_syscall_64+0x3b/0xc0
>>>    entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>   RIP: 0033:0x7fca6fc13912
>>>
>>> Return early when rmaps are not present.
>>>
>>> Reported-by: Vasant Hegde <vasant.hegde@....com>
>>> Tested-by: Vasant Hegde <vasant.hegde@....com>
>>> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
>>> ---
> 
> Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> 

Queued, thanks.

paolo