Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   "Li, Xin3" <xin3.li@intel.com>
To:     Thomas Gleixner <tglx@linutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
CC:     "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>,
        "jiangshanlai@gmail.com" <jiangshanlai@gmail.com>,
        "Kang, Shan" <shan.kang@intel.com>
Subject: RE: [PATCH v8 30/33] x86/fred: allow dynamic stack frame size
Thread-Topic: [PATCH v8 30/33] x86/fred: allow dynamic stack frame size
Thread-Index: AQHZa4iiz71eBkvk6ESYIcvcz1ZsbK98mC4AgAEFnqA=
Date:   Tue, 6 Jun 2023 06:18:21 +0000
Message-ID: <SA1PR11MB673430AC2D6F20C5F77FC83AA852A@SA1PR11MB6734.namprd11.prod.outlook.com>
References: <20230410081438.1750-1-xin3.li@intel.com>
 <20230410081438.1750-31-xin3.li@intel.com> <87wn0i578t.ffs@tglx>
In-Reply-To: <87wn0i578t.ffs@tglx>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?rAwaK0LR3XewxppwZE60wC2YjKq0D9Tke/Qljyg+IheokG8rXlBJAymjdLGD?=
 =?us-ascii?Q?Yb0/yVOut5DwF7FEc7Ip9HI8eMXvEHn+kZ7RyZ9QDuBA8dt7ZjaVTYxm9H12?=
 =?us-ascii?Q?fkChbhGK9X6aSH8i0khvuddooCCDgJSnU9bEIQas0BhkZIKtUCS5QjwJAeL4?=
 =?us-ascii?Q?FdPW7ivHxonFSTbg323mMbaIoHCwFxnyyTHXSsOmjaAZM1HfrYUXWVz9k+P5?=
 =?us-ascii?Q?T0Tp9mPGLR3bVIDVBOpvHiy88CrlXFSyQ8X15xwgPuNsqS2eA9MgKGmcgMZ7?=
 =?us-ascii?Q?fGBnFMXbg1rbtH92g9EK5M2locyTyYh908OK/ztsi6f2eOCps74veNEcFj2j?=
 =?us-ascii?Q?fN/T5c+M8cTIy1nL3GF5YClWy+tsQ8A0996RIZEyeYgK5dS6XxXjFZeZf4AE?=
 =?us-ascii?Q?slQQtIS3datyH+wvKVtTACQwvFGJhE+34FoFsudohcgQ9EMMVtmHnlbTS/EF?=
 =?us-ascii?Q?XGQyaCGeVtxb0/EPpbyEH+r4ir6bC5lud+kWes7S3pQf3rVk/ckKWQ1rim5L?=
 =?us-ascii?Q?j1Y6JE+uboE5HaEUg3X6v88ME7GRO2d9wzGa31gSkcGA1+seX/pIxQt6BMUJ?=
 =?us-ascii?Q?RMyChOw8AHH6j8S5hqn4BYxF2DJeUekktRJRCyk3jfDaqxXknJwdshERUImj?=
 =?us-ascii?Q?B+2NT0TzLbge2DvNHqmLITMCJoOtggZcLw2ggDXPBg2TZLNGwG2w/71PcKDj?=
 =?us-ascii?Q?MtF4Zx6X22aKpDsDrhwPbj+YUDaY88M8N118g7OMwH0xAXp0mYPexd6KBDd+?=
 =?us-ascii?Q?lDufiz+emDseHy5SSMC9nLyhSB7oX7qS/bK/x6QgxlNcqpc9MJ+ZCmE6z5KI?=
 =?us-ascii?Q?3OmJg6jHfQSIWzU27kQBRYvF9TzUEh6FPidQRRFYSLKZ6Wk0i8WCm6gNOeps?=
 =?us-ascii?Q?7SgTGJ/hrXgR41dadUFXsHOypDSv2X/R+y8gKULiRuaDQWMW6JLprX38fBLM?=
 =?us-ascii?Q?FBOT9o2OKj//cTLuuYZ/YGzcB7aTDLpeDf0ZXbnksZgKTlBU97oIPDuHWqUl?=
 =?us-ascii?Q?htCUzieukn0yIY8iiIubTtrZQYgGVGBelgov+4aOk7mXHJir7JGk/XuxgYNT?=
 =?us-ascii?Q?Kb1NMZuqq+VnUufxj/NEboqUTRJt27nEmVdSVjTLdtHlG37G2MHLmLLnVr7t?=
 =?us-ascii?Q?IRWVK2eji1nkRZwIqH2y5i34zs8dNNq1g5uADHGRD6TODq1nm94WYekMx0Cf?=
 =?us-ascii?Q?E5eZdBV+t4oRxsN6mdHNEi6vpORvbwbQ9n4Sj4Y0unYfymmbUEacRSBzpkDN?=
 =?us-ascii?Q?f+oUJI/Sa+J3EFsnbPnTZPVBxoRCa0N9w4SNko1UNdrHTQ5iWGaCmbYwQmjn?=
 =?us-ascii?Q?vkfDeAEYPHIgX4qM45MOybabr4LyBBop1CHSAEVKBmEW4PpP5zFLkesx7ce+?=
 =?us-ascii?Q?hSiNvzgjA7MA1fiz5/zRG/HBAs+Ut6NRMCB8Xr4cZBJM/JYOld4XGupRr3Yn?=
 =?us-ascii?Q?xpW1WAWvzw2ZtpL1YN8br2ARnDTEHilAj94xNFo5nGLS6iI2kLo/eaeWSGDT?=
 =?us-ascii?Q?7POIjJNQp74O+zBOwko/JNrnbT36c2fkLC42zM8uL6U1EwtLrepBUuGijzZI?=
 =?us-ascii?Q?judkYu+JULpM3Eblm9c=3D?=
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: SA1PR11MB6734.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 2918e6fb-734d-4054-a101-08db6655d400
X-MS-Exchange-CrossTenant-originalarrivaltime: 06 Jun 2023 06:18:21.7557
 (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: 3h9HlHSoufLCc+mSpwUMuugHPcfOPOv9VxnaIA4h2QPwYejxNKC35NlHEfp9ZHdmRjWfJdKyR7l/zcUh7AzFjQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR11MB7090
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,
        SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED
        autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> > A FRED stack frame could contain different amount of information for
> > different event types, or perhaps even for different instances of the
> > same event type. Thus we need to eliminate the need of any advance
> > information of the stack frame size to allow dynamic stack frame size.
> >
> > Implement it through:
> >   1) add a new field user_pt_regs to thread_info, and initialize it
> >      with a pointer to a virtual pt_regs structure at the top of a
> >      thread stack.
> >   2) save a pointer to the user-space pt_regs structure created by
> >      fred_entrypoint_user() to user_pt_regs in fred_entry_from_user().
> >   3) initialize the init_thread_info's user_pt_regs with a pointer to
> >      a virtual pt_regs structure at the top of init stack.
> >
> > This approach also works for IDT, thus we unify the code.
>=20
> And thereby remove the useful comment and replace it with an undocumented
> macro mess.
>=20
> I'm simply refusing to review this. It's not my job to understand this
> undocumented hackery.
>=20

I believe it's a nice idea to allow dynamic stack frame size, at least for
FRED. It's totally my bad that I didn't make it meet the minimum standards,
I will rewrite the commit message and add better comments.

After a second thought, I probably should only apply the change to FRED for
2 reasons, the change seems problematic with ESPFIX (which FRED doesn't nee=
d),
and such corner cases are hard to test (self-tests needed?).

Thanks!
Xin