Date:   Mon, 30 Jan 2023 14:19:03 +0800
From:   Chao Gao <chao.gao@intel.com>
To:     Kechen Lu <kechenl@nvidia.com>
CC:     <kvm@vger.kernel.org>, <seanjc@google.com>, <pbonzini@redhat.com>,
        <zhi.wang.linux@gmail.com>, <shaoqin.huang@intel.com>,
        <vkuznets@redhat.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v6 4/6] KVM: x86: Let userspace re-enable previously
 disabled exits
Message-ID: <Y9dhV3dBpRYQ2jJv@gao-cwp>
References: <20230121020738.2973-1-kechenl@nvidia.com>
 <20230121020738.2973-5-kechenl@nvidia.com>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20230121020738.2973-5-kechenl@nvidia.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?XkQowUNmsA7+DywSydaFng6FkpiLb/ZSqaEW8n11dN3k8GK5QsELQrxj6sh3?=
 =?us-ascii?Q?shd199Tu1VtF2ZD007WEP0oCkgUjYCI2Es8Z1BCFM8WnN140StUYyYeON66g?=
 =?us-ascii?Q?1XqbObCQOE48nY6YWMFIssuzF1OJlujozFAUbILFvX67dDThxxOkmAoHI23V?=
 =?us-ascii?Q?lwF3b/v6rB8Gd+3hoEZuSLGPd0Bd6IsITzTBpRBtcN8wr0fwd8un+665Cowu?=
 =?us-ascii?Q?2+LxR86k+cSpQ8zMvtBE7/YOknA6wX7HACUuMbqGoyyo7JeDAlgVxnF7N6+T?=
 =?us-ascii?Q?2+O6SGCfs/IEuyQTajb6Qy/OOAJdqYTdifmHZGdvieApWUnp9r9isbI3/LVc?=
 =?us-ascii?Q?SOFDEy6KYjO8wEGrcTnPoPkpQKB2pVd6jrRJdEFvSZK6v4jw7/XKPPnoStna?=
 =?us-ascii?Q?40KXBFjPCyf/Sj7OocyAqXnZw4VoL+rLuLZ3OIpog3JFifgbvb53/CvwLyEI?=
 =?us-ascii?Q?QXMx66DuCgrF2nZ8sXEsBAf1dcUuyQezKfywUUOTbdgpQfDS+uw+RS4KZAss?=
 =?us-ascii?Q?FppYQWoMXZwcxj8baQu2l5bwZuNHgO0Fe6/kI6QX/8Gy23L7uQNBR+NVg/2C?=
 =?us-ascii?Q?6MGt3mSCyz1w0MSlB1vqsuPlkk35xaiQdJvjboPxHQQtccXc89jCGOj5qi6v?=
 =?us-ascii?Q?H/IVEolbvxvlu9GMQOiRyxHQd9Ue9FHQSMuMqe3M69ECOyBLQdhwvf+GRXSO?=
 =?us-ascii?Q?dOJMpZKIKB2mQ+8OStj+/KxSSkPfXd9NE5lX2eyyjnakXO2siPP7lDnRCuig?=
 =?us-ascii?Q?BKngxKosS2FLqhT87sW3r9zPkKGDIN03/JVWPhZJ49G3MIs83abuvkXLVsBE?=
 =?us-ascii?Q?Oxe1Z/7e/dTciUVNn4keXAI7lff9hICD2AP15mmgFDe6VDQGdcRWYadzNwaV?=
 =?us-ascii?Q?aiYNGdRBy8Z9X+sCgRCM4ShK/fDp8jdYg93nff/XT6FMSGbZf2TYpSN1eCzF?=
 =?us-ascii?Q?C6sjGnn/sLK6cWBgriTa+1dpMXELOb1bfdvIlGBg0NIz2aj8/vQlqOnypuL8?=
 =?us-ascii?Q?7m9V2gClYLEDOGxTB1kOixcZf6lSKe0OJxFbn/67WKXQxh1U9Dgt8aGAUYdf?=
 =?us-ascii?Q?zs+WMZx8xGPPCCnmjq+jsRUDQURKzJt+6OwoosYk5Z61LDEerco5xhAqepLl?=
 =?us-ascii?Q?X7UW7mFAoCAYJIMZgtdRmMuNY2578ytBlSFT/uKSMTfA44mkn9UPBj6HKeeI?=
 =?us-ascii?Q?xpsp/4HNlwiAgrXIv6W3LsgN9T5RVlHRLVu6Zgvsygj/FUNlgyso5BZX5fH2?=
 =?us-ascii?Q?QqlJKiGd/u+EVFaQmCziAgK1UAQAF2vbgNA5mWku0dIguXzdlYJIxdVRlaMl?=
 =?us-ascii?Q?w0MUxYvgGt0eyoFigA4atckKZN7XkSufcCTTPOWIpZQlJPec4U89bA9HRMze?=
 =?us-ascii?Q?5W3BAj3S6XJijjdrfUhNAK9z90Gugf75CVY5n7hAjpvblrurscfySiksjytB?=
 =?us-ascii?Q?DUWzX4yhxlZvhktTfTOggTNNcl8hlQFWlgWAnqDJvOH75TqWHvIXfVKzCDRp?=
 =?us-ascii?Q?mYg9C0z/3+slV2Pc0tNy73fwf5GMuzq37OXZvLDqmPQnkTDL5TCHB5ZaaqDj?=
 =?us-ascii?Q?Aw/3PhtgDfCdB+yM8LaVKXHLlzNMDo3laiYMhTPU?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 21e28cde-cd93-4172-89f7-08db0289d97c
X-MS-Exchange-CrossTenant-AuthSource: PH8PR11MB6780.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Jan 2023 06:18:48.7537
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: tlu8s0j6sMxmShFBbbVdiL+DvPTYPrEvbN5GP20GZSz/aXygWImLlA8bulCFcRf9b7yjhSQHjsv6kzfyYEqQTg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR11MB6331
X-OriginatorOrg: intel.com
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sat, Jan 21, 2023 at 02:07:36AM +0000, Kechen Lu wrote:
>From: Sean Christopherson <seanjc@google.com>
>
>Add an OVERRIDE flag to KVM_CAP_X86_DISABLE_EXITS allow userspace to
>re-enable exits and/or override previous settings.  There's no real use
>case for the per-VM ioctl, but a future per-vCPU variant wants to let
>userspace toggle interception while the vCPU is running; add the OVERRIDE
>functionality now to provide consistent between the per-VM and
>per-vCPU variants.
>
>Signed-off-by: Sean Christopherson <seanjc@google.com>

Kechen, add your signed-off-by as you are the submitter.

>---
> Documentation/virt/kvm/api.rst |  5 +++++
> arch/x86/kvm/x86.c             | 32 ++++++++++++++++++++++++--------
> include/uapi/linux/kvm.h       |  4 +++-
> 3 files changed, 32 insertions(+), 9 deletions(-)
>
>diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
>index fb0fcc566d5a..3850202942d0 100644
>--- a/Documentation/virt/kvm/api.rst
>+++ b/Documentation/virt/kvm/api.rst
>@@ -7095,6 +7095,7 @@ Valid bits in args[0] are::
>   #define KVM_X86_DISABLE_EXITS_HLT              (1 << 1)
>   #define KVM_X86_DISABLE_EXITS_PAUSE            (1 << 2)
>   #define KVM_X86_DISABLE_EXITS_CSTATE           (1 << 3)
>+  #define KVM_X86_DISABLE_EXITS_OVERRIDE         (1ull << 63)
> 
> Enabling this capability on a VM provides userspace with a way to no
> longer intercept some instructions for improved latency in some
>@@ -7103,6 +7104,10 @@ physical CPUs.  More bits can be added in the future; userspace can
> just pass the KVM_CHECK_EXTENSION result to KVM_ENABLE_CAP to disable
> all such vmexits.
> 
>+By default, this capability only disables exits.  To re-enable an exit, or to
>+override previous settings, userspace can set KVM_X86_DISABLE_EXITS_OVERRIDE,
>+in which case KVM will enable/disable according to the mask (a '1' == disable).
>+
> Do not enable KVM_FEATURE_PV_UNHALT if you disable HLT exits.
> 
> 7.14 KVM_CAP_S390_HPAGE_1M
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index 60caa3fd40e5..3ea5f12536a0 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -5484,6 +5484,28 @@ static int kvm_vcpu_ioctl_device_attr(struct kvm_vcpu *vcpu,
> 	return r;
> }
> 
>+
>+#define kvm_ioctl_disable_exits(a, mask)				     \
>+({									     \

>+	if (!kvm_can_mwait_in_guest())                                       \
>+		(mask) &= KVM_X86_DISABLE_EXITS_MWAIT;                       \

This can be dropped or should be a WARN_ON_ONCE() because if kvm cannot
support mwait in guest (i.e., !kvm_can_mwait_in_guest()), attempts to
disable mwait exits are already treated as invalid requests in patch 3.

>+	if ((mask) & KVM_X86_DISABLE_EXITS_OVERRIDE) {			     \
>+		(a).mwait_in_guest = (mask) & KVM_X86_DISABLE_EXITS_MWAIT;   \
>+		(a).hlt_in_guest = (mask) & KVM_X86_DISABLE_EXITS_HLT;	     \
>+		(a).pause_in_guest = (mask) & KVM_X86_DISABLE_EXITS_PAUSE;   \
>+		(a).cstate_in_guest = (mask) & KVM_X86_DISABLE_EXITS_CSTATE; \
>+	} else {							     \
>+		if ((mask) & KVM_X86_DISABLE_EXITS_MWAIT)		     \
>+			(a).mwait_in_guest = true;			     \
>+		if ((mask) & KVM_X86_DISABLE_EXITS_HLT)			     \
>+			(a).hlt_in_guest = true;			     \
>+		if ((mask) & KVM_X86_DISABLE_EXITS_PAUSE)		     \
>+			(a).pause_in_guest = true;			     \
>+		if ((mask) & KVM_X86_DISABLE_EXITS_CSTATE)		     \
>+			(a).cstate_in_guest = true;			     \
>+	}								     \
>+})
>+
> static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
> 				     struct kvm_enable_cap *cap)
> {
>@@ -6238,14 +6260,8 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> 		if (kvm->created_vcpus)
> 			goto disable_exits_unlock;
> 
>-		if (cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT)
>-			kvm->arch.mwait_in_guest = true;
>-		if (cap->args[0] & KVM_X86_DISABLE_EXITS_HLT)
>-			kvm->arch.hlt_in_guest = true;
>-		if (cap->args[0] & KVM_X86_DISABLE_EXITS_PAUSE)
>-			kvm->arch.pause_in_guest = true;
>-		if (cap->args[0] & KVM_X86_DISABLE_EXITS_CSTATE)
>-			kvm->arch.cstate_in_guest = true;
>+		kvm_ioctl_disable_exits(kvm->arch, cap->args[0]);
>+
> 		r = 0;
> disable_exits_unlock:
> 		mutex_unlock(&kvm->lock);
>diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>index 55155e262646..876dcccbfff2 100644
>--- a/include/uapi/linux/kvm.h
>+++ b/include/uapi/linux/kvm.h
>@@ -823,10 +823,12 @@ struct kvm_ioeventfd {
> #define KVM_X86_DISABLE_EXITS_HLT            (1 << 1)
> #define KVM_X86_DISABLE_EXITS_PAUSE          (1 << 2)
> #define KVM_X86_DISABLE_EXITS_CSTATE         (1 << 3)
>+#define KVM_X86_DISABLE_EXITS_OVERRIDE	     (1ull << 63)
> #define KVM_X86_DISABLE_VALID_EXITS          (KVM_X86_DISABLE_EXITS_MWAIT | \
>                                               KVM_X86_DISABLE_EXITS_HLT | \
>                                               KVM_X86_DISABLE_EXITS_PAUSE | \
>-                                              KVM_X86_DISABLE_EXITS_CSTATE)
>+					      KVM_X86_DISABLE_EXITS_CSTATE | \
>+					      KVM_X86_DISABLE_EXITS_OVERRIDE)
> 
> /* for KVM_ENABLE_CAP */
> struct kvm_enable_cap {
>-- 
>2.34.1
>