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Date: Sat, 14 Oct 2017 12:25:20 +1100
From: Paul Mackerras <paulus@ozlabs.org>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org
Subject: Re: [PATCH kernel] KVM: PPC: Protect kvmppc_gpa_to_ua() with srcu
Message-ID: <20171014012520.GE26120@fergus.ozlabs.ibm.com>
References: <20171011050034.37872-1-aik@ozlabs.ru>
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On Wed, Oct 11, 2017 at 04:00:34PM +1100, Alexey Kardashevskiy wrote:
> kvmppc_gpa_to_ua() accesses KVM memory slot array via
> srcu_dereference_check() and this produces warnings from RCU like below.
> 
> This extends the existing srcu_read_lock/unlock to cover that
> kvmppc_gpa_to_ua() as well.
> 
> We did not hit this before as this lock is not needed for the realmode
> handlers and hash guests would use the realmode path all the time;
> however the radix guests are always redirected to the virtual mode
> handlers and hence the warning.
> 
> [   68.253798] ./include/linux/kvm_host.h:575 suspicious rcu_dereference_check() usage!
> [   68.253799]
>                other info that might help us debug this:
> 
> [   68.253802]
>                rcu_scheduler_active = 2, debug_locks = 1
> [   68.253804] 1 lock held by qemu-system-ppc/6413:
> [   68.253806]  #0:  (&vcpu->mutex){+.+.}, at: [<c00800000e3c22f4>] vcpu_load+0x3c/0xc0 [kvm]
> [   68.253826]
>                stack backtrace:
> [   68.253830] CPU: 92 PID: 6413 Comm: qemu-system-ppc Tainted: G        W       4.14.0-rc3-00553-g432dcba58e9c-dirty #72
> [   68.253833] Call Trace:
> [   68.253839] [c000000fd3d9f790] [c000000000b7fcc8] dump_stack+0xe8/0x160 (unreliable)
> [   68.253845] [c000000fd3d9f7d0] [c0000000001924c0] lockdep_rcu_suspicious+0x110/0x180
> [   68.253851] [c000000fd3d9f850] [c0000000000e825c] kvmppc_gpa_to_ua+0x26c/0x2b0
> [   68.253858] [c000000fd3d9f8b0] [c00800000e3e1984] kvmppc_h_put_tce+0x12c/0x2a0 [kvm]
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Thanks, applied to my kvm-ppc-fixes branch.

Paul.