Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755793AbcKOPsG (ORCPT ); Tue, 15 Nov 2016 10:48:06 -0500 Received: from merlin.infradead.org ([205.233.59.134]:37284 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753935AbcKOPsE (ORCPT ); Tue, 15 Nov 2016 10:48:04 -0500 Date: Tue, 15 Nov 2016 16:47:06 +0100 From: Peter Zijlstra To: Pan Xinhui Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, linux-s390@vger.kernel.org, xen-devel-request@lists.xenproject.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, mingo@redhat.com, paulmck@linux.vnet.ibm.com, will.deacon@arm.com, kernellwp@gmail.com, jgross@suse.com, pbonzini@redhat.com, bsingharora@gmail.com, boqun.feng@gmail.com, borntraeger@de.ibm.com, rkrcmar@redhat.com, David.Laight@ACULAB.COM, dave@stgolabs.net, konrad.wilk@oracle.com Subject: Re: [PATCH v7 06/11] x86, paravirt: Add interface to support kvm/xen vcpu preempted check Message-ID: <20161115154706.GF11311@worktop.programming.kicks-ass.net> References: <1478077718-37424-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <1478077718-37424-7-git-send-email-xinhui.pan@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1478077718-37424-7-git-send-email-xinhui.pan@linux.vnet.ibm.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7821 Lines: 260 On Wed, Nov 02, 2016 at 05:08:33AM -0400, Pan Xinhui wrote: > diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h > index 0f400c0..38c3bb7 100644 > --- a/arch/x86/include/asm/paravirt_types.h > +++ b/arch/x86/include/asm/paravirt_types.h > @@ -310,6 +310,8 @@ struct pv_lock_ops { > > void (*wait)(u8 *ptr, u8 val); > void (*kick)(int cpu); > + > + bool (*vcpu_is_preempted)(int cpu); > }; So that ends up with a full function call in the native case. I did something like the below on top, completely untested, not been near a compiler etc.. It doesn't get rid of the branch, but at least it avoids the function call, and hardware should have no trouble predicting a constant condition. Also, it looks like you end up not setting vcpu_is_preempted when KVM doesn't support steal clock, which would end up in an instant NULL deref. Fixed that too. --- --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -673,6 +673,11 @@ static __always_inline void pv_kick(int PVOP_VCALL1(pv_lock_ops.kick, cpu); } +static __always_inline void pv_vcpu_is_prempted(int cpu) +{ + PVOP_VCALLEE1(pv_lock_ops.vcpu_is_preempted, cpu); +} + #endif /* SMP && PARAVIRT_SPINLOCKS */ #ifdef CONFIG_X86_32 --- a/arch/x86/include/asm/paravirt_types.h +++ b/arch/x86/include/asm/paravirt_types.h @@ -309,7 +309,7 @@ struct pv_lock_ops { void (*wait)(u8 *ptr, u8 val); void (*kick)(int cpu); - bool (*vcpu_is_preempted)(int cpu); + struct paravirt_callee_save vcpu_is_preempted; }; /* This contains all the paravirt structures: we get a convenient --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -32,6 +32,12 @@ static inline void queued_spin_unlock(st { pv_queued_spin_unlock(lock); } + +#define vcpu_is_preempted vcpu_is_preempted +static inline bool vcpu_is_preempted(int cpu) +{ + return pv_vcpu_is_preempted(cpu); +} #else static inline void queued_spin_unlock(struct qspinlock *lock) { --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -26,14 +26,6 @@ extern struct static_key paravirt_ticketlocks_enabled; static __always_inline bool static_key_false(struct static_key *key); -#ifdef CONFIG_PARAVIRT_SPINLOCKS -#define vcpu_is_preempted vcpu_is_preempted -static inline bool vcpu_is_preempted(int cpu) -{ - return pv_lock_ops.vcpu_is_preempted(cpu); -} -#endif - #include /* --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -415,15 +415,6 @@ void kvm_disable_steal_time(void) wrmsr(MSR_KVM_STEAL_TIME, 0, 0); } -static bool kvm_vcpu_is_preempted(int cpu) -{ - struct kvm_steal_time *src; - - src = &per_cpu(steal_time, cpu); - - return !!src->preempted; -} - #ifdef CONFIG_SMP static void __init kvm_smp_prepare_boot_cpu(void) { @@ -480,9 +471,6 @@ void __init kvm_guest_init(void) if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { has_steal_clock = 1; pv_time_ops.steal_clock = kvm_steal_clock; -#ifdef CONFIG_PARAVIRT_SPINLOCKS - pv_lock_ops.vcpu_is_preempted = kvm_vcpu_is_preempted; -#endif } if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) @@ -604,6 +592,14 @@ static void kvm_wait(u8 *ptr, u8 val) local_irq_restore(flags); } +static bool __kvm_vcpu_is_preempted(int cpu) +{ + struct kvm_steal_time *src = &per_cpu(steal_time, cpu); + + return !!src->preempted; +} +PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); + /* * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present. */ @@ -620,6 +616,12 @@ void __init kvm_spinlock_init(void) pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); pv_lock_ops.wait = kvm_wait; pv_lock_ops.kick = kvm_kick_cpu; + pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(__native_vcpu_is_preempted); + + if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { + pv_lock_ops.vcpu_is_preempted = + PV_CALLEE_SAVE(__kvm_vcpu_is_preempted); + } } static __init int kvm_spinlock_init_jump(void) --- a/arch/x86/kernel/paravirt-spinlocks.c +++ b/arch/x86/kernel/paravirt-spinlocks.c @@ -12,7 +12,6 @@ __visible void __native_queued_spin_unlo { native_queued_spin_unlock(lock); } - PV_CALLEE_SAVE_REGS_THUNK(__native_queued_spin_unlock); bool pv_is_native_spin_unlock(void) @@ -21,9 +20,16 @@ bool pv_is_native_spin_unlock(void) __raw_callee_save___native_queued_spin_unlock; } -static bool native_vcpu_is_preempted(int cpu) +__visible bool __native_vcpu_is_preempted(int cpu) { - return 0; + return false; +} +PV_CALLEE_SAVE_REGS_THUNK(__native_vcpu_is_preempted); + +bool pv_is_native_vcpu_is_preempted(void) +{ + return pv_lock_ops.queued_spin_unlock.func == + __raw_callee_save__native_vcpu_is_preempted; } struct pv_lock_ops pv_lock_ops = { @@ -32,7 +38,7 @@ struct pv_lock_ops pv_lock_ops = { .queued_spin_unlock = PV_CALLEE_SAVE(__native_queued_spin_unlock), .wait = paravirt_nop, .kick = paravirt_nop, - .vcpu_is_preempted = native_vcpu_is_preempted, + .vcpu_is_preempted = PV_CALLEE_SAVE(__native_vcpu_is_preempted), #endif /* SMP */ }; EXPORT_SYMBOL(pv_lock_ops); --- a/arch/x86/kernel/paravirt_patch_32.c +++ b/arch/x86/kernel/paravirt_patch_32.c @@ -11,6 +11,7 @@ DEF_NATIVE(pv_mmu_ops, read_cr3, "mov %c #if defined(CONFIG_PARAVIRT_SPINLOCKS) DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%eax)"); +DEF_NATIVE(pv_lock_ops, vcpu_is_preempted, "movl $0, %eax"); #endif unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len) @@ -26,6 +27,7 @@ unsigned paravirt_patch_ident_64(void *i } extern bool pv_is_native_spin_unlock(void); +extern bool pv_is_native_vcpu_is_preempted(void); unsigned native_patch(u8 type, u16 clobbers, void *ibuf, unsigned long addr, unsigned len) @@ -54,6 +56,12 @@ unsigned native_patch(u8 type, u16 clobb end = end_pv_lock_ops_queued_spin_unlock; goto patch_site; } + case PARAVIRT_PATCH(pv_lock_ops.vcpu_is_preempted): + if (pv_is_native_vcpu_is_preempted()) { + start = start_pv_lock_ops_vcpu_is_preempted; + end = end_pv_lock_ops_vcpu_is_preempted; + goto patch_site; + } #endif default: --- a/arch/x86/kernel/paravirt_patch_64.c +++ b/arch/x86/kernel/paravirt_patch_64.c @@ -20,6 +20,7 @@ DEF_NATIVE(, mov64, "mov %rdi, %rax"); #if defined(CONFIG_PARAVIRT_SPINLOCKS) DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%rdi)"); +DEF_NATIVE(pv_lock_ops, vcpu_is_preempted, "movl $0, rax"); #endif unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len) @@ -35,6 +36,7 @@ unsigned paravirt_patch_ident_64(void *i } extern bool pv_is_native_spin_unlock(void); +extern bool pv_is_native_vcpu_is_preempted(void); unsigned native_patch(u8 type, u16 clobbers, void *ibuf, unsigned long addr, unsigned len) @@ -66,6 +68,12 @@ unsigned native_patch(u8 type, u16 clobb end = end_pv_lock_ops_queued_spin_unlock; goto patch_site; } + case PARAVIRT_PATCH(pv_lock_ops.vcpu_is_preempted): + if (pv_is_native_vcpu_is_preempted()) { + start = start_pv_lock_ops_vcpu_is_preempted; + end = end_pv_lock_ops_vcpu_is_preempted; + goto patch_site; + } #endif default: --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -114,6 +114,8 @@ void xen_uninit_lock_cpu(int cpu) per_cpu(irq_name, cpu) = NULL; } +PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); + /* * Our init of PV spinlocks is split in two init functions due to us * using paravirt patching and jump labels patching and having to do @@ -136,8 +138,7 @@ void __init xen_init_spinlocks(void) pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); pv_lock_ops.wait = xen_qlock_wait; pv_lock_ops.kick = xen_qlock_kick; - - pv_lock_ops.vcpu_is_preempted = xen_vcpu_stolen; + pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); } /*