From patchwork Mon Nov 6 20:26:20 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Eduardo Valentin X-Patchwork-Id: 10044425 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 85DD46032D for ; Mon, 6 Nov 2017 20:28:54 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 7991329BBE for ; Mon, 6 Nov 2017 20:28:54 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 6E43E29FE1; Mon, 6 Nov 2017 20:28:54 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D955529FE0 for ; Mon, 6 Nov 2017 20:28:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932869AbdKFU2k (ORCPT ); Mon, 6 Nov 2017 15:28:40 -0500 Received: from smtp-fw-2101.amazon.com ([72.21.196.25]:38404 "EHLO smtp-fw-2101.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932837AbdKFU2j (ORCPT ); Mon, 6 Nov 2017 15:28:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1510000118; x=1541536118; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=UjkGvgsou0A1G7iBUXDdqgnFPEm1o1fqfk4709Ldt90=; b=pzdeGtDmzgAl8/Pp4KRbUvxPRvd1BXUkCgk7o73aLy7UIDdIG2Mgk42S wERZjP4glE4xuosXrkJzqvcbEyZD/kWn1NPwdbtZZfF2hassUwjZyBqcO iEqAx2BehIuk9D5jQkjQ5VsZg5e/Ol5Hjc/QU/rH9P7sa39VdR5kVcJIl A=; X-IronPort-AV: E=Sophos;i="5.44,354,1505779200"; d="scan'208";a="662309912" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-1d-2c665b5d.us-east-1.amazon.com) ([10.43.8.6]) by smtp-border-fw-out-2101.iad2.amazon.com with ESMTP/TLS/DHE-RSA-AES256-SHA; 06 Nov 2017 20:26:38 +0000 Received: from EX13MTAUWB001.ant.amazon.com (iad55-ws-svc-p15-lb9-vlan3.iad.amazon.com [10.40.159.166]) by email-inbound-relay-1d-2c665b5d.us-east-1.amazon.com (8.14.7/8.14.7) with ESMTP id vA6KQKkL111417 (version=TLSv1/SSLv3 cipher=AES256-SHA bits=256 verify=FAIL); Mon, 6 Nov 2017 20:26:25 GMT Received: from EX13D05UWB001.ant.amazon.com (10.43.161.181) by EX13MTAUWB001.ant.amazon.com (10.43.161.249) with Microsoft SMTP Server (TLS) id 15.0.1236.3; Mon, 6 Nov 2017 20:26:24 +0000 Received: from EX13MTAUEA001.ant.amazon.com (10.43.61.82) by EX13D05UWB001.ant.amazon.com (10.43.161.181) with Microsoft SMTP Server (TLS) id 15.0.1236.3; Mon, 6 Nov 2017 20:26:24 +0000 Received: from localhost (10.85.17.193) by mail-relay.amazon.com (10.43.61.243) with Microsoft SMTP Server id 15.0.1236.3 via Frontend Transport; Mon, 6 Nov 2017 20:26:22 +0000 From: Eduardo Valentin To: Paolo Bonzini , CC: Matt Wilson , Eduardo Valentin , Jonathan Corbet , Thomas Gleixner , "Ingo Molnar" , "H. Peter Anvin" , , Peter Zijlstra , Waiman Long , , , , "Jan H . Schoenherr" , Anthony Liguori Subject: [PATCHv3 1/1] locking/qspinlock/x86: Avoid test-and-set when PV_DEDICATED is set Date: Mon, 6 Nov 2017 12:26:20 -0800 Message-ID: <1509999980-10828-1-git-send-email-eduval@amazon.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Currently, the existing qspinlock implementation will fallback to test-and-set if the hypervisor has not set the PV_UNHALT flag. This patch gives the opportunity to guest kernels to select between test-and-set and the regular queueu fair lock implementation based on the PV_DEDICATED KVM feature flag. When the PV_DEDICATED flag is not set, the code will still fall back to test-and-set, but when the PV_DEDICATED flag is set, the code will use the regular queue spinlock implementation. With this patch, when in autoselect mode, the guest will use the default spinlock implementation based on host feature flags as follows: PV_DEDICATED = 1, PV_UNHALT = anything: default is qspinlock PV_DEDICATED = 0, PV_UNHALT = 1: default is pvqspinlock PV_DEDICATED = 0, PV_UNHALT = 0: default is tas Cc: Paolo Bonzini Cc: "Radim Krčmář" Cc: Jonathan Corbet Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: Peter Zijlstra Cc: Waiman Long Cc: kvm@vger.kernel.org Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: Jan H. Schoenherr Cc: Anthony Liguori Suggested-by: Matt Wilson Signed-off-by: Eduardo Valentin --- V3: - When PV_DEDICATED is set (1), qspinlock is selected, regardless of the value of PV_UNHAULT. Suggested by Paolo Bonzini. - Refreshed on top of tip/master. V2: - rebase on top of tip/master Documentation/virtual/kvm/cpuid.txt | 6 ++++++ arch/x86/include/asm/qspinlock.h | 4 ++++ arch/x86/include/uapi/asm/kvm_para.h | 1 + arch/x86/kernel/kvm.c | 2 ++ 4 files changed, 13 insertions(+) diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index 3c65feb..117066a 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -54,6 +54,12 @@ KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit || || before enabling paravirtualized || || spinlock support. ------------------------------------------------------------------------------ +KVM_FEATURE_PV_DEDICATED || 8 || guest checks this feature bit + || || to determine if they run on + || || dedicated vCPUs, allowing opti- + || || mizations such as usage of + || || qspinlocks. +------------------------------------------------------------------------------ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index 5e16b5d..de42694 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -3,6 +3,8 @@ #define _ASM_X86_QSPINLOCK_H #include +#include + #include #include #include @@ -58,6 +60,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock) if (!static_branch_likely(&virt_spin_lock_key)) return false; + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) + return false; /* * On hypervisors without PARAVIRT_SPINLOCKS support we fall * back to a Test-and-Set spinlock, because fair locks have diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h index 554aa8f..85a9875 100644 --- a/arch/x86/include/uapi/asm/kvm_para.h +++ b/arch/x86/include/uapi/asm/kvm_para.h @@ -25,6 +25,7 @@ #define KVM_FEATURE_STEAL_TIME 5 #define KVM_FEATURE_PV_EOI 6 #define KVM_FEATURE_PV_UNHALT 7 +#define KVM_FEATURE_PV_DEDICATED 8 /* The last 8 bits are used to indicate how to interpret the flags field * in pvclock structure. If no bits are set, all flags are ignored. diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 8bb9594..dacd7cf 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -642,6 +642,8 @@ void __init kvm_spinlock_init(void) { if (!kvm_para_available()) return; + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) + return; /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) return;