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

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Message-ID: <Ydhx1qguxVZxOGfo@google.com>
Date:   Fri, 7 Jan 2022 17:01:10 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Nikunj A Dadhania <nikunj@....com>,
        Paolo Bonzini <pbonzini@...hat.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 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>