From patchwork Tue Dec 19 16:11:07 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Durrant X-Patchwork-Id: 13498515 Received: from mail.xenproject.org (mail.xenproject.org [104.130.215.37]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87C8D37D12; Tue, 19 Dec 2023 16:41:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=xen.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=xen.org header.i=@xen.org header.b="ffWhzPNp" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:MIME-Version:References: In-Reply-To:Message-Id:Date:Subject:To:From; bh=Pp1Na6ZPy28QqQdGJl0/7AJNoR5iWhhLtNjZDP6VEBI=; b=ffWhzPNpz37pCRS0eQZxO4AuBB nFBLcxqh5C71F8t0hTzN4SFKOCuKPZ53SiYKqDisfliuljggzvidL6L5dAOOvB6gpnNNVyogRHg6L +ctnEyFOYNZZCiDQLcTQR7T5aTv7RmDKPXcbmzZeQreAN7/kwzz4kW16WxvGIpXD3kp4=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1rFd9x-00064t-TG; Tue, 19 Dec 2023 16:41:33 +0000 Received: from 54-240-197-226.amazon.com ([54.240.197.226] helo=REM-PW02S00X.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1rFckP-0005h9-Iw; Tue, 19 Dec 2023 16:15:09 +0000 From: Paul Durrant To: Paolo Bonzini , Jonathan Corbet , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , David Woodhouse , Paul Durrant , Shuah Khan , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v11 17/19] KVM: xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast() Date: Tue, 19 Dec 2023 16:11:07 +0000 Message-Id: <20231219161109.1318-18-paul@xen.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231219161109.1318-1-paul@xen.org> References: <20231219161109.1318-1-paul@xen.org> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Paul Durrant As described in [1] compiling with CONFIG_PROVE_RAW_LOCK_NESTING shows that kvm_xen_set_evtchn_fast() is blocking on pfncache locks in IRQ context. There is only actually blocking with PREEMPT_RT because the locks will turned into mutexes. There is no 'raw' version of rwlock_t that can be used to avoid that, so use read_trylock() and treat failure to lock the same as an invalid cache. [1] https://lore.kernel.org/lkml/99771ef3a4966a01fefd3adbb2ba9c3a75f97cf2.camel@infradead.org/T/#mbd06e5a04534ce9c0ee94bd8f1e8d942b2d45bd6 Signed-off-by: Paul Durrant Reviewed-by: David Woodhouse --- Cc: Sean Christopherson Cc: Paolo Bonzini Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: David Woodhouse Cc: x86@kernel.org v11: - Amended the commit comment. v10: - New in this version. --- arch/x86/kvm/xen.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index 4ebd24c3ae70..845ff23c8399 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1675,10 +1675,13 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) unsigned long flags; int rc = -EWOULDBLOCK; - read_lock_irqsave(&gpc->lock, flags); - if (!kvm_gpc_check(gpc, PAGE_SIZE)) + local_irq_save(flags); + if (!read_trylock(&gpc->lock)) goto out; + if (!kvm_gpc_check(gpc, PAGE_SIZE)) + goto out_unlock; + if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) { struct shared_info *shinfo = gpc->khva; @@ -1700,8 +1703,10 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) rc = 1; /* It is newly raised */ } + out_unlock: + read_unlock(&gpc->lock); out: - read_unlock_irqrestore(&gpc->lock, flags); + local_irq_restore(flags); return rc; } @@ -1711,21 +1716,23 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) struct gfn_to_pfn_cache *gpc = &vcpu->arch.xen.vcpu_info_cache; unsigned long flags; bool kick_vcpu = false; + bool locked; - read_lock_irqsave(&gpc->lock, flags); + local_irq_save(flags); + locked = read_trylock(&gpc->lock); /* * Try to deliver the event directly to the vcpu_info. If successful and * the guest is using upcall_vector delivery, send the MSI. - * If the pfncache is invalid, set the shadow. In this case, or if the - * guest is using another form of event delivery, the vCPU must be - * kicked to complete the delivery. + * If the pfncache lock is contended or the cache is invalid, set the + * shadow. In this case, or if the guest is using another form of event + * delivery, the vCPU must be kicked to complete the delivery. */ if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) { struct vcpu_info *vcpu_info = gpc->khva; int port_word_bit = port / 64; - if (!kvm_gpc_check(gpc, sizeof(*vcpu_info))) { + if ((!locked || !kvm_gpc_check(gpc, sizeof(*vcpu_info)))) { if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel)) kick_vcpu = true; goto out; @@ -1739,7 +1746,7 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) struct compat_vcpu_info *vcpu_info = gpc->khva; int port_word_bit = port / 32; - if (!kvm_gpc_check(gpc, sizeof(*vcpu_info))) { + if ((!locked || !kvm_gpc_check(gpc, sizeof(*vcpu_info)))) { if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel)) kick_vcpu = true; goto out; @@ -1758,7 +1765,10 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) } out: - read_unlock_irqrestore(&gpc->lock, flags); + if (locked) + read_unlock(&gpc->lock); + + local_irq_restore(flags); return kick_vcpu; }