From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (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 9518B19F495; Tue, 25 Feb 2025 07:00:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740466817; cv=none; b=MNt9MXORUs8mkUnq5+0RDv76/WJfRaYMvJzH6MrJ1D4uneqWrCJgsiJARTKGcGmL6fROWpgcxwPO47ugeWblVtIqoDolYwXyTXb35VfijnBPvOcqZIQqL4LC1jtItlqZeWYYrhcETjfwcVDgoHW1r37jzleo1rVzrK2byWLblJY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740466817; c=relaxed/simple; bh=Jm9aY5N8Dq6B/Se5BKvQ1YCroA5kAnewWsbVHEv5BFQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BW4hTlrWSH3UNVleYcxMF3jkPRAwq4PmOh20JLcDCfh2iCpraiVx1m291pfh4oBg8ohUtQZrBmK1jPp46UJXRjpztEw4kSN+Aw4oq+siTdOXw0oiMUQX6Wt4uwb+wcGYp7TjTjvH0D9ClrPFSsseb9s6tSlXpCz8wGftFrurRTQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=W4iaVXM3; arc=none smtp.client-ip=192.198.163.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="W4iaVXM3" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1740466816; x=1772002816; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=Jm9aY5N8Dq6B/Se5BKvQ1YCroA5kAnewWsbVHEv5BFQ=; b=W4iaVXM3kIa2Q1Kz8QITLF7kDRIJDa+aTZUUbDdt33hvRqCtIlAARU8/ KjCyY/X92nNsG9rZvn9p/vdq5Y5HU46Yni1kN8yna17jM5sXfXX7eztFm 8aH9cmtHz5L6HHPD4n1DNUbVk2FW7hniJ1BFHAFA/HFOUeJja/WZWEGwn C/POyYrC8oWh21YJ2oezNeJDVhDwt7h5hxjLbG6Wzxxk30e2hIFz9qWQO 9kgtBK4MH6Szg6i1C6sH0XrzmsVEZ9HkVDnSr35aaLBS2xmRJeNNkIcSU 1KFEVIfabtl3xXY2Da3sOy5tDg8CwRhI1Etnq3+w4lTJ2Nz6KCFJL9RXG Q==; X-CSE-ConnectionGUID: kjaD/FYuTsWUGz2SqNQANw== X-CSE-MsgGUID: Epq0gFQgRXSrRVs9qgNydw== X-IronPort-AV: E=McAfee;i="6700,10204,11355"; a="41139948" X-IronPort-AV: E=Sophos;i="6.13,313,1732608000"; d="scan'208";a="41139948" Received: from orviesa003.jf.intel.com ([10.64.159.143]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Feb 2025 23:00:13 -0800 X-CSE-ConnectionGUID: WV/FS0LjRB2TisF+x+zDLg== X-CSE-MsgGUID: oJ4khU6BQ8OOcG0mMINBsg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.13,313,1732608000"; d="scan'208";a="121242251" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.124.247.1]) ([10.124.247.1]) by ORVIESA003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Feb 2025 23:00:07 -0800 Message-ID: <84cc95e6-74a5-47b2-9f36-ae33f1e8b5c8@intel.com> Date: Tue, 25 Feb 2025 15:00:03 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2 08/12] KVM: x86: Allow to update cached values in kvm_user_return_msrs w/o wrmsr To: Adrian Hunter , pbonzini@redhat.com, seanjc@google.com Cc: kvm@vger.kernel.org, rick.p.edgecombe@intel.com, kai.huang@intel.com, reinette.chatre@intel.com, tony.lindgren@linux.intel.com, binbin.wu@linux.intel.com, dmatlack@google.com, isaku.yamahata@intel.com, nik.borisov@suse.com, linux-kernel@vger.kernel.org, yan.y.zhao@intel.com, chao.gao@intel.com, weijiang.yang@intel.com References: <20250129095902.16391-1-adrian.hunter@intel.com> <20250129095902.16391-9-adrian.hunter@intel.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: <20250129095902.16391-9-adrian.hunter@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/29/2025 5:58 PM, Adrian Hunter wrote: > From: Chao Gao > > Several MSRs are constant and only used in userspace(ring 3). But VMs may > have different values. KVM uses kvm_set_user_return_msr() to switch to > guest's values and leverages user return notifier to restore them when the > kernel is to return to userspace. To eliminate unnecessary wrmsr, KVM also > caches the value it wrote to an MSR last time. > > TDX module unconditionally resets some of these MSRs to architectural INIT > state on TD exit. It makes the cached values in kvm_user_return_msrs are > inconsistent with values in hardware. This inconsistency needs to be > fixed. Otherwise, it may mislead kvm_on_user_return() to skip restoring > some MSRs to the host's values. kvm_set_user_return_msr() can help correct > this case, but it is not optimal as it always does a wrmsr. So, introduce > a variation of kvm_set_user_return_msr() to update cached values and skip > that wrmsr. > > Signed-off-by: Chao Gao > Signed-off-by: Isaku Yamahata > Signed-off-by: Adrian Hunter > Reviewed-by: Paolo Bonzini Reviewed-by: Xiaoyao Li > --- > TD vcpu enter/exit v2: > - No changes > > TD vcpu enter/exit v1: > - Rename functions and remove useless comment (Binbin) > --- > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/x86.c | 24 +++++++++++++++++++----- > 2 files changed, 20 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 6b686d62c735..e557a441fade 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -2322,6 +2322,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, > int kvm_add_user_return_msr(u32 msr); > int kvm_find_user_return_msr(u32 msr); > int kvm_set_user_return_msr(unsigned index, u64 val, u64 mask); > +void kvm_user_return_msr_update_cache(unsigned int index, u64 val); > > static inline bool kvm_is_supported_user_return_msr(u32 msr) > { > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 5cf9f023fd4b..15447fe7687c 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -636,6 +636,15 @@ static void kvm_user_return_msr_cpu_online(void) > } > } > > +static void kvm_user_return_register_notifier(struct kvm_user_return_msrs *msrs) > +{ > + if (!msrs->registered) { > + msrs->urn.on_user_return = kvm_on_user_return; > + user_return_notifier_register(&msrs->urn); > + msrs->registered = true; > + } > +} > + > int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask) > { > struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs); > @@ -649,15 +658,20 @@ int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask) > return 1; > > msrs->values[slot].curr = value; > - if (!msrs->registered) { > - msrs->urn.on_user_return = kvm_on_user_return; > - user_return_notifier_register(&msrs->urn); > - msrs->registered = true; > - } > + kvm_user_return_register_notifier(msrs); > return 0; > } > EXPORT_SYMBOL_GPL(kvm_set_user_return_msr); > > +void kvm_user_return_msr_update_cache(unsigned int slot, u64 value) > +{ > + struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs); > + > + msrs->values[slot].curr = value; > + kvm_user_return_register_notifier(msrs); > +} > +EXPORT_SYMBOL_GPL(kvm_user_return_msr_update_cache); > + > static void drop_user_return_notifiers(void) > { > struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);