From: Paolo Bonzini <pbonzini@redhat.com>
To: Nikunj A Dadhania <nikunj@amd.com>
Cc: Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Peter Xu <peterx@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
vasant.hegde@amd.com, brijesh.singh@amd.com
Subject: Re: [PATCH v2] KVM: x86: Check for rmaps allocation
Date: Fri, 7 Jan 2022 18:08:50 +0100 [thread overview]
Message-ID: <6867e529-a85d-72fe-4577-55a4e793ba31@redhat.com> (raw)
In-Reply-To: <20220105040337.4234-1-nikunj@amd.com>
On 1/5/22 05:03, 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@amd.com>
> Tested-by: Vasant Hegde <vasant.hegde@amd.com>
> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
> ---
>
> v1: https://lore.kernel.org/kvm/20220104092814.11553-1-nikunj@amd.com/T/#u
>
> Check the rmaps inside kvm_mmu_rmaps_stat_show() as the rmaps can be
> allocated dynamically (Peter Xu)
>
> arch/x86/kvm/debugfs.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
> index 543a8c04025c..9240b3b7f8dd 100644
> --- a/arch/x86/kvm/debugfs.c
> +++ b/arch/x86/kvm/debugfs.c
> @@ -95,6 +95,9 @@ static int kvm_mmu_rmaps_stat_show(struct seq_file *m, void *v)
> unsigned int *log[KVM_NR_PAGE_SIZES], *cur;
> int i, j, k, l, ret;
>
> + if (!kvm_memslots_have_rmaps(kvm))
> + return 0;
> +
> ret = -ENOMEM;
> memset(log, 0, sizeof(log));
> for (i = 0; i < KVM_NR_PAGE_SIZES; i++) {
Queued, thanks.
Paolo
prev parent reply other threads:[~2022-01-07 17:08 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-05 4:03 [PATCH v2] KVM: x86: Check for rmaps allocation Nikunj A Dadhania
2022-01-05 9:07 ` Peter Xu
2022-01-07 17:01 ` Sean Christopherson
2022-01-07 17:03 ` Paolo Bonzini
2022-01-07 17:04 ` Paolo Bonzini
2022-01-07 17:08 ` Paolo Bonzini [this message]
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