From: "Nikunj A. Dadhania" <nikunj@amd.com>
To: Peter Xu <peterx@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
vasant.hegde@amd.com, brijesh.singh@amd.com
Subject: Re: [PATCH] KVM: x86: Do not create mmu_rmaps_stat for TDP MMU
Date: Tue, 4 Jan 2022 16:08:14 +0530 [thread overview]
Message-ID: <eb3e95fc-0c05-f0f9-1801-92ec9b5f5845@amd.com> (raw)
In-Reply-To: <YdQYK4oRDU2Dmfwe@xz-m1.local>
Hi Peter,
On 1/4/2022 3:19 PM, Peter Xu wrote:
> Hi, Nikunj,
>
> On Tue, Jan 04, 2022 at 02:58:14PM +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
>>
>> Create mmu_rmaps_stat debugfs file only when rmaps are created.
>>
>> Reported-by: Vasant Hegde <vasant.hegde@amd.com>
>> Tested-by: Vasant Hegde <vasant.hegde@amd.com>
>> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
>
> Shall we put the check into kvm_mmu_rmaps_stat_show()? As iiuc the rmap can be
> allocated dynamically (shadow_root_allocated changing from 0->1).
Yes, that will cover the above case. And mmu_rmaps_stat file will be empty
in case when rmaps are not allocated.
Regards
Nikunj
prev parent reply other threads:[~2022-01-04 10:38 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-04 9:28 Nikunj A Dadhania
2022-01-04 9:49 ` Peter Xu
2022-01-04 10:38 ` Nikunj A. Dadhania [this message]
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