linux-kernel - Re: [PATCH 00/44] KVM: Rework kvm

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Message-ID: <9890f67846f1c2c6a12bd086fc822f0762966223.camel@intel.com>
Date:   Tue, 8 Nov 2022 08:56:58 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>
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Subject: Re: [PATCH 00/44] KVM: Rework kvm_init() and hardware enabling

On Mon, 2022-11-07 at 21:43 -0800, Isaku Yamahata wrote:
> On Tue, Nov 08, 2022 at 01:09:27AM +0000,
> "Huang, Kai" <kai.huang@...el.com> wrote:
> 
> > On Mon, 2022-11-07 at 13:46 -0800, Isaku Yamahata wrote:
> > > > On Fri, Nov 04, 2022, Isaku Yamahata wrote:
> > > > > Thanks for the patch series. I the rebased TDX KVM patch series and it
> > > > > worked.
> > > > > Since cpu offline needs to be rejected in some cases(To keep at least one
> > > > > cpu
> > > > > on a package), arch hook for cpu offline is needed.
> > > > 
> > > > I hate to bring this up because I doubt there's a real use case for SUSPEND
> > > > with
> > > > TDX, but the CPU offline path isn't just for true offlining of CPUs.  When
> > > > the
> > > > system enters SUSPEND, only the initiating CPU goes through
> > > > kvm_suspend()+kvm_resume(),
> > > > all responding CPUs go through CPU offline+online.  I.e. disallowing all
> > > > CPUs from
> > > > going "offline" will prevent suspending the system.
> > > 
> > > The current TDX KVM implementation disallows CPU package from offline only
> > > when
> > > TDs are running.  If no TD is running, CPU offline is allowed.  So before
> > > SUSPEND, TDs need to be killed via systemd or something.  After killing TDs,
> > > the
> > > system can enter into SUSPEND state.
> > 
> > This seems not correct.  You need one cpu for each to be online in order to
> > create TD as well, as TDH.MNG.KEY.CONFIG needs to be called on all packages,
> > correct?
> 
> That's correct. In such case, the creation of TD fails.  TD creation checks if
> at least one cpu is online on all CPU packages.  If no, error.

I think we can just always refuse to offline the last cpu for each package when
TDX is enabled.  It's simpler I guess.