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From: "Laszlo Ersek" <lersek@redhat.com>
To: "Kinney, Michael D" <michael.d.kinney@intel.com>,
	"Yao, Jiewen" <jiewen.yao@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"rfc@edk2.groups.io" <rfc@edk2.groups.io>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	"devel@edk2.groups.io" <devel@edk2.groups.io>,
	qemu devel list <qemu-devel@nongnu.org>,
	Igor Mammedov <imammedo@redhat.com>,
	"Chen, Yingwen" <yingwen.chen@intel.com>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Joao Marcal Lemos Martins <joao.m.martins@oracle.com>,
	Phillip Goerl <phillip.goerl@oracle.com>
Subject: Re: [edk2-rfc] [edk2-devel] CPU hotplug using SMM with QEMU+OVMF
Date: Mon, 26 Aug 2019 17:30:43 +0200	[thread overview]
Message-ID: <ea0330f1-cb6a-2a45-f8e7-3de19b117e77@redhat.com> (raw)
In-Reply-To: <E92EE9817A31E24EB0585FDF735412F5B9DA25CC@ORSMSX113.amr.corp.intel.com>

On 08/23/19 17:25, Kinney, Michael D wrote:
> Hi Jiewen,
> 
> If a hot add CPU needs to run any code before the
> first SMI, I would recommend is only executes code
> from a write protected FLASH range without a stack
> and then wait for the first SMI.

"without a stack" looks very risky to me. Even if we manage to implement
the guest code initially, we'll be trapped without a stack, should we
ever need to add more complex stuff there.


> For this OVMF use case, is any CPU init required
> before the first SMI?

I expressed a preference for that too: "I wish we could simply wake the
new CPU [...] with an SMI".

http://mid.mail-archive.com/398b3327-0820-95af-a34d-1a4a1d50cf35@redhat.com


> From Paolo's list of steps are steps (8a) and (8b) 
> really required?

See again my message linked above -- just after the quoted sentence, I
wrote, "IOW, if we could excise steps 07b, 08a, 08b".

But, I obviously defer to Paolo and Igor on that.

(I do believe we have a dilemma here. In QEMU, we probably prefer to
emulate physical hardware as faithfully as possible. However, we do not
have Cache-As-RAM (nor do we intend to, IIUC). Does that justify other
divergences from physical hardware too, such as waking just by virtue of
an SMI?)


> Can the SMI monarch use the Local
> APIC to send a directed SMI to the hot added CPU?
> The SMI monarch needs to know the APIC ID of the
> hot added CPU.  Do we also need to handle the case
> where multiple CPUs are added at once?  I think we
> would need to serialize the use of 3000:8000 for the
> SMM rebase operation on each hot added CPU.

I agree this would be a huge help.


> It would be simpler if we can guarantee that only
> one CPU can be added or removed at a time and the 
> complete flow of adding a CPU to SMM and the OS
> needs to be completed before another add/remove
> event needs to be processed.

I don't know if the QEMU monitor command in question can guarantee this
serialization. I think such a request/response pattern is generally
implementable between QEMU and guest code.

But, AIUI, the "device-add" monitor command is quite generic, and used
for hot-plugging a number of other (non-CPU) device models. I'm unsure
if the pattern in question can be squeezed into "device-add". (It's not
a dedicated command for CPU hotplug.)

... Apologies that I didn't add much information to the thread, just
now. I'd like to keep the discussion going.

Thanks
Laszlo

  parent reply	other threads:[~2019-08-26 15:30 UTC|newest]

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-13 14:16 CPU hotplug using SMM with QEMU+OVMF Laszlo Ersek
2019-08-13 16:09 ` Laszlo Ersek
2019-08-13 16:18   ` Laszlo Ersek
2019-08-14 13:20   ` Yao, Jiewen
2019-08-14 14:04     ` Paolo Bonzini
2019-08-15  9:55       ` Yao, Jiewen
2019-08-15 16:04         ` Paolo Bonzini
2019-08-15 15:00       ` [edk2-devel] " Laszlo Ersek
2019-08-15 16:16         ` Igor Mammedov
2019-08-15 16:21         ` Paolo Bonzini
2019-08-16  2:46           ` Yao, Jiewen
2019-08-16  7:20             ` Paolo Bonzini
2019-08-16  7:49               ` Yao, Jiewen
2019-08-16 20:15                 ` Laszlo Ersek
2019-08-16 22:19                   ` Alex Williamson
2019-08-17  0:20                     ` Yao, Jiewen
2019-08-18 19:50                       ` Paolo Bonzini
2019-08-18 23:00                         ` Yao, Jiewen
2019-08-19 14:10                           ` Paolo Bonzini
2019-08-21 12:07                             ` Laszlo Ersek
2019-08-21 15:48                           ` [edk2-rfc] " Michael D Kinney
2019-08-21 17:05                             ` Paolo Bonzini
2019-08-21 17:25                               ` Michael D Kinney
2019-08-21 17:39                                 ` Paolo Bonzini
2019-08-21 20:17                                   ` Michael D Kinney
2019-08-22  6:18                                     ` Paolo Bonzini
2019-08-22 18:29                                       ` Laszlo Ersek
2019-08-22 18:51                                         ` Paolo Bonzini
2019-08-23 14:53                                           ` Laszlo Ersek
2019-08-22 20:13                                         ` Michael D Kinney
2019-08-22 17:59                               ` Laszlo Ersek
2019-08-22 18:43                                 ` Paolo Bonzini
2019-08-22 20:06                                   ` Michael D Kinney
2019-08-22 22:18                                     ` Paolo Bonzini
2019-08-22 22:32                                       ` Michael D Kinney
2019-08-22 23:11                                         ` Paolo Bonzini
2019-08-23  1:02                                           ` Michael D Kinney
2019-08-23  5:00                                             ` Yao, Jiewen
2019-08-23 15:25                                               ` Michael D Kinney
2019-08-24  1:48                                                 ` Yao, Jiewen
2019-08-27 18:31                                                   ` Igor Mammedov
2019-08-29 17:01                                                     ` Laszlo Ersek
2019-08-30 14:48                                                       ` Igor Mammedov
2019-08-30 18:46                                                         ` Laszlo Ersek
2019-09-02  8:45                                                           ` Igor Mammedov
2019-09-02 19:09                                                             ` Laszlo Ersek
2019-09-03 14:53                                                               ` [Qemu-devel] " Igor Mammedov
2019-09-03 17:20                                                                 ` Laszlo Ersek
2019-09-04  9:52                                                                   ` imammedo
2019-09-05 13:08                                                                     ` Laszlo Ersek
2019-09-05 15:45                                                                       ` Igor Mammedov
2019-09-05 15:49                                                                       ` [PATCH] q35: lpc: allow to lock down 128K RAM at default SMBASE address Igor Mammedov
2019-09-09 19:15                                                                         ` Laszlo Ersek
2019-09-09 19:20                                                                           ` Laszlo Ersek
2019-09-10 15:58                                                                           ` Igor Mammedov
2019-09-11 17:30                                                                             ` Laszlo Ersek
2019-09-17 13:11                                                                               ` [edk2-devel] " Igor Mammedov
2019-09-17 14:38                                                                                 ` [staging/branch]: CdePkg - C Development Environment Package Minnow Ware
2019-08-26 15:30                                                 ` Laszlo Ersek [this message]
2019-08-27 16:23                                                   ` [edk2-rfc] [edk2-devel] CPU hotplug using SMM with QEMU+OVMF Igor Mammedov
2019-08-27 20:11                                                     ` Laszlo Ersek
2019-08-28 12:01                                                       ` Igor Mammedov
2019-08-29 16:25                                                         ` Laszlo Ersek
2019-08-30 13:49                                                           ` [Qemu-devel] " Igor Mammedov
2019-08-22 17:53                             ` Laszlo Ersek
2019-08-16 20:00           ` Laszlo Ersek
2019-08-15 16:07       ` Igor Mammedov
2019-08-15 16:24         ` Paolo Bonzini
2019-08-16  7:42           ` Igor Mammedov

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