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From: Kai Huang <kai.huang@intel.com>
To: Dave Hansen <dave.hansen@intel.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: seanjc@google.com, pbonzini@redhat.com, len.brown@intel.com,
	tony.luck@intel.com, rafael.j.wysocki@intel.com,
	reinette.chatre@intel.com, dan.j.williams@intel.com,
	peterz@infradead.org, ak@linux.intel.com,
	kirill.shutemov@linux.intel.com,
	sathyanarayanan.kuppuswamy@linux.intel.com,
	isaku.yamahata@intel.com
Subject: Re: [PATCH v3 04/21] x86/virt/tdx: Add skeleton for detecting and initializing TDX on demand
Date: Fri, 29 Apr 2022 12:11:17 +1200	[thread overview]
Message-ID: <af6fccf2f6f8d83593f0eedd003c7cd07f89274d.camel@intel.com> (raw)
In-Reply-To: <0aa81fd0-a491-847d-9fc6-4b853f2cf7b4@intel.com>

On Thu, 2022-04-28 at 16:53 -0700, Dave Hansen wrote:
> On 4/28/22 16:44, Kai Huang wrote:
> > > Just like the SME test, it doesn't even need to be precise.  It just
> > > needs to be 100% accurate in that it is *ALWAYS* set for any system that
> > > might have dirtied cache aliases.
> > > 
> > > I'm not sure why you are so fixated on SEAMRR specifically for this.
> > I see.  I think I can simply use MTRR.SEAMRR bit check.  If CPU supports SEAMRR,
> > then basically it supports MKTME.
> > 
> > Is this look good for you?
> 
> Sure, fine, as long as it comes with a coherent description that
> explains why the check is good enough.
> 
> > > > "During initializing the TDX module, one step requires some SEAMCALL must be
> > > > done on all logical cpus enabled by BIOS, otherwise a later step will fail. 
> > > > Disable CPU hotplug during the initialization process to prevent any CPU going
> > > > offline during initializing the TDX module.  Note it is caller's responsibility
> > > > to guarantee all BIOS-enabled CPUs are in cpu_present_mask and all present CPUs
> > > > are online."
> > > But, what if a CPU went offline just before this lock was taken?  What
> > > if the caller make sure all present CPUs are online, makes the call,
> > > then a CPU is taken offline.  The lock wouldn't do any good.
> > > 
> > > What purpose does the lock serve?
> > I thought cpus_read_lock() can prevent any CPU from going offline, no?
> 
> It doesn't prevent squat before the lock is taken, though.

This is true.  So I think w/o taking the lock is also fine, as the TDX module
initialization is a state machine.  If any cpu goes offline during logical-cpu
level initialization and TDH.SYS.LP.INIT isn't done on that cpu, then later the
TDH.SYS.CONFIG will fail.  Similarly, if any cpu going offline causes
TDH.SYS.KEY.CONFIG is not done for any package, then TDH.SYS.TDMR.INIT will
fail.

A problem (I realized it exists in current implementation too) is shutting down
the TDX module, which requires calling TDH.SYS.LP.SHUTDOWN on all BIOS-enabled
cpus.  Kernel can do this SEAMCALL at most for all present cpus.  However when
any cpu is offline, this SEAMCALL won't be called on it, and it seems we need to
add new CPU hotplug callback to call this SEAMCALL when the cpu is online again.

Any suggestion?  Thanks!


-- 
Thanks,
-Kai



  reply	other threads:[~2022-04-29  0:11 UTC|newest]

Thread overview: 156+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-06  4:49 [PATCH v3 00/21] TDX host kernel support Kai Huang
2022-04-06  4:49 ` [PATCH v3 01/21] x86/virt/tdx: Detect SEAM Kai Huang
2022-04-18 22:29   ` Sathyanarayanan Kuppuswamy
2022-04-18 22:50     ` Sean Christopherson
2022-04-19  3:38     ` Kai Huang
2022-04-26 20:21   ` Dave Hansen
2022-04-26 23:12     ` Kai Huang
2022-04-26 23:28       ` Dave Hansen
2022-04-26 23:49         ` Kai Huang
2022-04-27  0:22           ` Sean Christopherson
2022-04-27  0:44             ` Kai Huang
2022-04-27 14:22           ` Dave Hansen
2022-04-27 22:39             ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 02/21] x86/virt/tdx: Detect TDX private KeyIDs Kai Huang
2022-04-19  5:39   ` Sathyanarayanan Kuppuswamy
2022-04-19  9:41     ` Kai Huang
2022-04-19  5:42   ` Sathyanarayanan Kuppuswamy
2022-04-19 10:07     ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 03/21] x86/virt/tdx: Implement the SEAMCALL base function Kai Huang
2022-04-19 14:07   ` Sathyanarayanan Kuppuswamy
2022-04-20  4:16     ` Kai Huang
2022-04-20  7:29       ` Sathyanarayanan Kuppuswamy
2022-04-20 10:39         ` Kai Huang
2022-04-26 20:37   ` Dave Hansen
2022-04-26 23:29     ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 04/21] x86/virt/tdx: Add skeleton for detecting and initializing TDX on demand Kai Huang
2022-04-19 14:53   ` Sathyanarayanan Kuppuswamy
2022-04-20  4:37     ` Kai Huang
2022-04-20  5:21       ` Dave Hansen
2022-04-20 14:30       ` Sathyanarayanan Kuppuswamy
2022-04-20 22:35         ` Kai Huang
2022-04-26 20:53   ` Dave Hansen
2022-04-27  0:43     ` Kai Huang
2022-04-27 14:49       ` Dave Hansen
2022-04-28  0:00         ` Kai Huang
2022-04-28 14:27           ` Dave Hansen
2022-04-28 23:44             ` Kai Huang
2022-04-28 23:53               ` Dave Hansen
2022-04-29  0:11                 ` Kai Huang [this message]
2022-04-29  0:26                   ` Dave Hansen
2022-04-29  0:59                     ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 05/21] x86/virt/tdx: Detect P-SEAMLDR and TDX module Kai Huang
2022-04-26 20:56   ` Dave Hansen
2022-04-27  0:01     ` Kai Huang
2022-04-27 14:24       ` Dave Hansen
2022-04-27 21:30         ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 06/21] x86/virt/tdx: Shut down TDX module in case of error Kai Huang
2022-04-23 15:39   ` Sathyanarayanan Kuppuswamy
2022-04-25 23:41     ` Kai Huang
2022-04-26  1:48       ` Sathyanarayanan Kuppuswamy
2022-04-26  2:12         ` Kai Huang
2022-04-26 20:59   ` Dave Hansen
2022-04-27  0:06     ` Kai Huang
2022-05-18 16:19       ` Sagi Shahar
2022-05-18 23:51         ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 07/21] x86/virt/tdx: Do TDX module global initialization Kai Huang
2022-04-20 22:27   ` Sathyanarayanan Kuppuswamy
2022-04-20 22:37     ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 08/21] x86/virt/tdx: Do logical-cpu scope TDX module initialization Kai Huang
2022-04-24  1:27   ` Sathyanarayanan Kuppuswamy
2022-04-25 23:55     ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 09/21] x86/virt/tdx: Get information about TDX module and convertible memory Kai Huang
2022-04-25  2:58   ` Sathyanarayanan Kuppuswamy
2022-04-26  0:05     ` Kai Huang
2022-04-27 22:15   ` Dave Hansen
2022-04-28  0:15     ` Kai Huang
2022-04-28 14:06       ` Dave Hansen
2022-04-28 23:14         ` Kai Huang
2022-04-29 17:47           ` Dave Hansen
2022-05-02  5:04             ` Kai Huang
2022-05-25  4:47             ` Kai Huang
2022-05-25  4:57               ` Kai Huang
2022-05-25 16:00                 ` Kai Huang
2022-05-18 22:30       ` Sagi Shahar
2022-05-18 23:56         ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 10/21] x86/virt/tdx: Add placeholder to coveret all system RAM as TDX memory Kai Huang
2022-04-20 20:48   ` Isaku Yamahata
2022-04-20 22:38     ` Kai Huang
2022-04-27 22:24   ` Dave Hansen
2022-04-28  0:53     ` Kai Huang
2022-04-28  1:07       ` Dave Hansen
2022-04-28  1:35         ` Kai Huang
2022-04-28  3:40           ` Dave Hansen
2022-04-28  3:55             ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 11/21] x86/virt/tdx: Choose to use " Kai Huang
2022-04-20 20:55   ` Isaku Yamahata
2022-04-20 22:39     ` Kai Huang
2022-04-28 15:54   ` Dave Hansen
2022-04-29  7:32     ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 12/21] x86/virt/tdx: Create TDMRs to cover all system RAM Kai Huang
2022-04-28 16:22   ` Dave Hansen
2022-04-29  7:24     ` Kai Huang
2022-04-29 13:52       ` Dave Hansen
2022-04-06  4:49 ` [PATCH v3 13/21] x86/virt/tdx: Allocate and set up PAMTs for TDMRs Kai Huang
2022-04-28 17:12   ` Dave Hansen
2022-04-29  7:46     ` Kai Huang
2022-04-29 14:20       ` Dave Hansen
2022-04-29 14:30         ` Sean Christopherson
2022-04-29 17:46           ` Dave Hansen
2022-04-29 18:19             ` Sean Christopherson
2022-04-29 18:32               ` Dave Hansen
2022-05-02  5:59         ` Kai Huang
2022-05-02 14:17           ` Dave Hansen
2022-05-02 21:55             ` Kai Huang
2022-04-06  4:49 ` [PATCH v3 14/21] x86/virt/tdx: Set up reserved areas for all TDMRs Kai Huang
2022-04-06  4:49 ` [PATCH v3 15/21] x86/virt/tdx: Reserve TDX module global KeyID Kai Huang
2022-04-06  4:49 ` [PATCH v3 16/21] x86/virt/tdx: Configure TDX module with TDMRs and " Kai Huang
2022-04-06  4:49 ` [PATCH v3 17/21] x86/virt/tdx: Configure global KeyID on all packages Kai Huang
2022-04-06  4:49 ` [PATCH v3 18/21] x86/virt/tdx: Initialize all TDMRs Kai Huang
2022-04-06  4:49 ` [PATCH v3 19/21] x86: Flush cache of TDX private memory during kexec() Kai Huang
2022-04-06  4:49 ` [PATCH v3 20/21] x86/virt/tdx: Add kernel command line to opt-in TDX host support Kai Huang
2022-04-28 17:25   ` Dave Hansen
2022-04-06  4:49 ` [PATCH v3 21/21] Documentation/x86: Add documentation for " Kai Huang
2022-04-14 10:19 ` [PATCH v3 00/21] TDX host kernel support Kai Huang
2022-04-26 20:13 ` Dave Hansen
2022-04-27  1:15   ` Kai Huang
2022-04-27 21:59     ` Dave Hansen
2022-04-28  0:37       ` Kai Huang
2022-04-28  0:50         ` Dave Hansen
2022-04-28  0:58           ` Kai Huang
2022-04-29  1:40             ` Kai Huang
2022-04-29  3:04               ` Dan Williams
2022-04-29  5:35                 ` Kai Huang
2022-05-03 23:59               ` Kai Huang
2022-05-04  0:25                 ` Dave Hansen
2022-05-04  1:15                   ` Kai Huang
2022-05-05  9:54                     ` Kai Huang
2022-05-05 13:51                       ` Dan Williams
2022-05-05 22:14                         ` Kai Huang
2022-05-06  0:22                           ` Dan Williams
2022-05-06  0:45                             ` Kai Huang
2022-05-06  1:15                               ` Dan Williams
2022-05-06  1:46                                 ` Kai Huang
2022-05-06 15:57                                   ` Dan Williams
2022-05-09  2:46                                     ` Kai Huang
2022-05-10 10:25                                       ` Kai Huang
2022-05-07  0:09                         ` Mike Rapoport
2022-05-08 10:00                           ` Kai Huang
2022-05-09 10:33                             ` Mike Rapoport
2022-05-09 23:27                               ` Kai Huang
2022-05-04 14:31                 ` Dan Williams
2022-05-04 22:50                   ` Kai Huang
2022-04-28  1:01   ` Dan Williams
2022-04-28  1:21     ` Kai Huang
2022-04-29  2:58       ` Dan Williams
2022-04-29  5:43         ` Kai Huang
2022-04-29 14:39         ` Dave Hansen
2022-04-29 15:18           ` Dan Williams
2022-04-29 17:18             ` Dave Hansen
2022-04-29 17:48               ` Dan Williams
2022-04-29 18:34                 ` Dave Hansen
2022-04-29 18:47                   ` Dan Williams
2022-04-29 19:20                     ` Dave Hansen
2022-04-29 21:20                       ` Dan Williams
2022-04-29 21:27                         ` Dave Hansen
2022-05-02 10:18                   ` Kai Huang

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