From nobody Fri Apr 10 20:28:25 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A6C33C25B08 for ; Sat, 20 Aug 2022 06:00:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244430AbiHTGAw (ORCPT ); Sat, 20 Aug 2022 02:00:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229458AbiHTGAt (ORCPT ); Sat, 20 Aug 2022 02:00:49 -0400 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED3A2A2237; Fri, 19 Aug 2022 23:00:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1660975248; x=1692511248; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=8uxTMc931N62LSyYSZec4Q6h4MH1p09mPLFpxJiMDMs=; b=CewhIl6ghhuIdaGvkrFc4OZFbfbIEDYwG4QF6MlW8onpRE+uQEiqXNLf g206XtIrrsdHcVnR94dGVJ4pGFKKdBneQwc1SFt89R6kEo6awZ6usb8m+ g2aXbzOfmvqENu/N6NZC+6Rq3YkDgEeav5Wf+iRf8FaJzYKBlfGUjBQZw M5jY12bnFW8kU58OSY6RFtyi54JDHJYO8zQTD/i3PwADUKg67nbMTgwmf RDO0nJBU2bUfWtlBAffuZc3ZMQgAf3OAiA42j/Sm8YcsL0H0TB+HA5Q5a WESY5/aLZqFdJnAUWAWYm5ylQ+54l4EbFhL7Aeg5zzYw0k3cG5mxIvLo4 w==; X-IronPort-AV: E=McAfee;i="6500,9779,10444"; a="379448966" X-IronPort-AV: E=Sophos;i="5.93,250,1654585200"; d="scan'208";a="379448966" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2022 23:00:48 -0700 X-IronPort-AV: E=Sophos;i="5.93,250,1654585200"; d="scan'208";a="668857511" Received: from ls.sc.intel.com (HELO localhost) ([143.183.96.54]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2022 23:00:48 -0700 From: isaku.yamahata@intel.com To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: isaku.yamahata@intel.com, isaku.yamahata@gmail.com, Paolo Bonzini , Sean Christopherson , Kai Huang , Chao Gao , Will Deacon Subject: [RFC PATCH 01/18] KVM: x86: Drop kvm_user_return_msr_cpu_online() Date: Fri, 19 Aug 2022 23:00:07 -0700 Message-Id: <9e0f84ece483bfeffe7e0b254363845af910ea84.1660974106.git.isaku.yamahata@intel.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Isaku Yamahata KVM/X86 uses user return notifier to switch MSR for guest or user space. Snapshot host values on CPU online, change MSR values for guest, and restore them on returning to user space. The current code abuses kvm_arch_hardware_enable() which is called on kvm module initialization or CPU online. Remove such the abuse of kvm_arch_hardware_enable by capturing the host value on the first change of the MSR value to guest VM instead of CPU online. Suggested-by: Sean Christopherson Signed-off-by: Isaku Yamahata --- arch/x86/kvm/x86.c | 43 ++++++++++++++++++++++++------------------- 1 file changed, 24 insertions(+), 19 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 205ebdc2b11b..16104a2f7d8e 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -200,6 +200,7 @@ struct kvm_user_return_msrs { struct kvm_user_return_msr_values { u64 host; u64 curr; + bool initialized; } values[KVM_MAX_NR_USER_RETURN_MSRS]; }; =20 @@ -363,6 +364,10 @@ static void kvm_on_user_return(struct user_return_noti= fier *urn) local_irq_restore(flags); for (slot =3D 0; slot < kvm_nr_uret_msrs; ++slot) { values =3D &msrs->values[slot]; + /* + * No need to check values->initialized because host =3D curr =3D 0 + * by __GFP_ZERO when !values->initialized. + */ if (values->host !=3D values->curr) { wrmsrl(kvm_uret_msrs_list[slot], values->host); values->curr =3D values->host; @@ -409,34 +414,30 @@ int kvm_find_user_return_msr(u32 msr) } EXPORT_SYMBOL_GPL(kvm_find_user_return_msr); =20 -static void kvm_user_return_msr_cpu_online(void) -{ - unsigned int cpu =3D smp_processor_id(); - struct kvm_user_return_msrs *msrs =3D per_cpu_ptr(user_return_msrs, cpu); - u64 value; - int i; - - for (i =3D 0; i < kvm_nr_uret_msrs; ++i) { - rdmsrl_safe(kvm_uret_msrs_list[i], &value); - msrs->values[i].host =3D value; - msrs->values[i].curr =3D value; - } -} - int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask) { unsigned int cpu =3D smp_processor_id(); struct kvm_user_return_msrs *msrs =3D per_cpu_ptr(user_return_msrs, cpu); + struct kvm_user_return_msr_values *values =3D &msrs->values[slot]; int err; =20 - value =3D (value & mask) | (msrs->values[slot].host & ~mask); - if (value =3D=3D msrs->values[slot].curr) + if (unlikely(!values->initialized)) { + u64 host_value; + + rdmsrl_safe(kvm_uret_msrs_list[slot], &host_value); + values->host =3D host_value; + values->curr =3D host_value; + values->initialized =3D true; + } + + value =3D (value & mask) | (values->host & ~mask); + if (value =3D=3D values->curr) return 0; err =3D wrmsrl_safe(kvm_uret_msrs_list[slot], value); if (err) return 1; =20 - msrs->values[slot].curr =3D value; + values->curr =3D value; if (!msrs->registered) { msrs->urn.on_user_return =3D kvm_on_user_return; user_return_notifier_register(&msrs->urn); @@ -9212,7 +9213,12 @@ int kvm_arch_init(void *opaque) return -ENOMEM; } =20 - user_return_msrs =3D alloc_percpu(struct kvm_user_return_msrs); + /* + * __GFP_ZERO to ensure user_return_msrs.values[].{host, curr} match. + * See kvm_on_user_return() + */ + user_return_msrs =3D alloc_percpu_gfp(struct kvm_user_return_msrs, + GFP_KERNEL | __GFP_ZERO); if (!user_return_msrs) { printk(KERN_ERR "kvm: failed to allocate percpu kvm_user_return_msrs\n"); r =3D -ENOMEM; @@ -11836,7 +11842,6 @@ int kvm_arch_hardware_enable(void) u64 max_tsc =3D 0; bool stable, backwards_tsc =3D false; =20 - kvm_user_return_msr_cpu_online(); ret =3D static_call(kvm_x86_hardware_enable)(); if (ret !=3D 0) return ret; --=20 2.25.1