linux-kernel - Re: powerpc KVM build break in linux-next (was Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling)

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Message-Id: <20170421041754.GV3956@linux.vnet.ibm.com>
Date:   Thu, 20 Apr 2017 21:17:54 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Michael Ellerman <michaele@....ibm.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, tglx@...utronix.de,
        kvm@...r.kernel.org, oleg@...hat.com, peterz@...radead.org,
        fweisbec@...il.com, bobby.prani@...il.com, jiangshanlai@...il.com,
        linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org,
        josh@...htriplett.org, dhowells@...hat.com, edumazet@...gle.com,
        "paulus@...ba.org" <paulus@...ba.org>, rostedt@...dmis.org,
        dipankar@...ibm.com, mathieu.desnoyers@...icios.com,
        akpm@...ux-foundation.org,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        mingo@...nel.org
Subject: Re: powerpc KVM build break in linux-next (was Re: [PATCH
 tip/core/rcu 40/40] srcu: Parallelize callback handling)

On Fri, Apr 21, 2017 at 11:42:01AM +1000, Michael Ellerman wrote:
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> writes:
> > On Thu, Apr 20, 2017 at 05:28:32PM +0200, Paolo Bonzini wrote:
> >> On 20/04/2017 05:40, Michael Ellerman wrote:
> >> > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> writes:
> >> > 
> >> > This change seems to have had the non-obvious effect of breaking the
> >> > powerpc KVM build.
> ...
> >> 
> >> Michael, if you want to move the two srcu structs at the end of struct
> >> kvm, that would be fine by me.  Please send a patch yourself so you can
> >> test it on PPC.  Thanks,
> >
> > On the off-chance that it is at all helpful, I have added the commit
> > shown below to -rcu.
> 
> As shown below :)
> 
> > If it helps, I am happy to push this, but am just as happy to drop it
> > in favor of some other fix. If at all possible, I would like to get
> > this into the upcoming merge window.
> 
> Thanks, this looks perfect to me, and if you're happy to put it on top
> of your tree that would limit the breakage to a smaller history window,
> so that would be ideal.
> 
> Tested-by: Michael Ellerman <mpe@...erman.id.au>

Thank you, Michael!

Paolo, does this look good to you?  My upstream maintainer will be much
more likely to take this with your ack.  ;-)

							Thanx, Paul

> cheers
> 
> 
> >From a19a6617e2817e485ccc2f7cc5a97bd7ff769b87 Mon Sep 17 00:00:00 2001
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Date: Thu, 20 Apr 2017 17:30:06 -0700
> Subject: kvm: Move srcu_struct fields to end of struct kvm
> 
> Parallelizing SRCU callback handling increased the size of srcu_struct,
> which moved the kvm_arch field within the kvm struct out of reach of
> powerpc's current assembly code, resulting in the following sort of
> build error:
> 
> arch/powerpc/kvm/book3s_hv_rmhandlers.S:617: Error: operand out of range (0x000000000000b328 is not between 0xffffffffffff8000 and 0x0000000000007fff)
> 
> This commit moves the srcu_struct fields in the kvm structure to follow
> the kvm_arch field, which again allows powerpc's assembly code to
> reach it.
> 
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Reported-by: Michael Ellerman <michaele@....ibm.com>
> Reported-by: kbuild test robot <fengguang.wu@...el.com>
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  include/linux/kvm_host.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 2c14ad9..96c8e29 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -375,8 +375,6 @@ struct kvm {
>  	struct mutex slots_lock;
>  	struct mm_struct *mm; /* userspace tied to this vm */
>  	struct kvm_memslots *memslots[KVM_ADDRESS_SPACE_NUM];
> -	struct srcu_struct srcu;
> -	struct srcu_struct irq_srcu;
>  	struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
> 
>  	/*
> @@ -429,6 +427,8 @@ struct kvm {
>  	struct list_head devices;
>  	struct dentry *debugfs_dentry;
>  	struct kvm_stat_data **debugfs_stat_data;
> +	struct srcu_struct srcu;
> +	struct srcu_struct irq_srcu;
>  };
> 
>  #define kvm_err(fmt, ...) \
> -- 
> cgit v1.1