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Date: Thu, 20 Apr 2017 17:38:34 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Paolo Bonzini <pbonzini@...hat.com> Cc: Michael Ellerman <michaele@....ibm.com>, linux-kernel@...r.kernel.org, "paulus@...ba.org" <paulus@...ba.org>, kvm@...r.kernel.org, kvm-ppc@...r.kernel.org, "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com Subject: Re: powerpc KVM build break in linux-next (was Re: [PATCH tip/core/rcu 40/40] srcu: Parallelize callback handling) 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: > > > >> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h > >> index f2b3bd6c6bc2..0400e211aa44 100644 > >> --- a/include/linux/srcutree.h > >> +++ b/include/linux/srcutree.h > >> @@ -24,25 +24,75 @@ > > ... > >> +/* > >> + * Per-SRCU-domain structure, similar in function to rcu_state. > >> + */ > >> struct srcu_struct { > >> - unsigned long completed; > >> - unsigned long srcu_gp_seq; > >> - atomic_t srcu_exp_cnt; > >> - struct srcu_array __percpu *per_cpu_ref; > >> - spinlock_t queue_lock; /* protect ->srcu_cblist */ > >> - struct rcu_segcblist srcu_cblist; > >> + struct srcu_node node[NUM_RCU_NODES]; /* Combining tree. */ > >> + struct srcu_node *level[RCU_NUM_LVLS + 1]; > >> + /* First node at each level. */ > >> + struct mutex srcu_cb_mutex; /* Serialize CB preparation. */ > >> + spinlock_t gp_lock; /* protect ->srcu_cblist */ > >> + struct mutex srcu_gp_mutex; /* Serialize GP work. */ > >> + unsigned int srcu_idx; /* Current rdr array element. */ > >> + unsigned long srcu_gp_seq; /* Grace-period seq #. */ > >> + unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */ > >> + atomic_t srcu_exp_cnt; /* # ongoing expedited GPs. */ > >> + struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ > >> + unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */ > >> + struct mutex srcu_barrier_mutex; /* Serialize barrier ops. */ > >> + struct completion srcu_barrier_completion; > >> + /* Awaken barrier rq at end. */ > >> + atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */ > >> + /* callback for the barrier */ > >> + /* operation. */ > > > > This change seems to have had the non-obvious effect of breaking the > > powerpc KVM build. > > > > Because struct kvm contains two srcu_structs which are located > > before the kvm_arch struct, the increase in size of srcu_struct has > > caused the offset from the start of struct kvm to kvm_arch to be too big > > for some of our asm. > > > > struct kvm { > > spinlock_t mmu_lock; > > 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_arch arch; > > > > > > Example error: > > arch/powerpc/kvm/book3s_hv_rmhandlers.S:617: Error: operand out of range (0x000000000000b328 is not between 0xffffffffffff8000 and 0x0000000000007fff) > > > > Where line 617 is: > > lwz r7,KVM_LPID(r9) > > > > And the KVM_LPID constant comes from asm-offsets.s. The diff of old vs > > new is: > > > > -->KVM_LPID 17752 offsetof(struct kvm, arch.lpid) # > > +->KVM_LPID 45864 offsetof(struct kvm, arch.lpid) # > > > > > > We can probably just fix it by changing the asm to keep the address of > > kvm_arch in a register, and then offset from that. > > 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. 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. Thanx, Paul
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