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From: Thomas Gleixner <tglx@linutronix.de>
To: speck@linutronix.de
Subject: Re: L1D-Fault KVM mitigation
Date: Sun, 27 May 2018 20:57:45 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1805272055540.1585@nanos.tec.linutronix.de> (raw)
In-Reply-To: <alpine.LFD.2.21.999.1805271131170.18753@i7.lan>

On Sun, 27 May 2018, speck for Linus Torvalds wrote:
> On Sun, 27 May 2018, speck for Andi Kleen wrote:
> > > 
> > > Maybe you mean "idle in the _host_"?
> > 
> > It's both actually. Either idle in the host, or idle in the guest.
> 
> It really really isn't.
> 
> Andi, if one sibling does a vmexit, and the other sibling is still in vmx 
> mode, we have to force-exit the other sibling. It doesn't matter one whit 
> whether it's idle or not - because we won't know.
> 
> Or is there some magical sideband that I am not aware of?
> 
> > When it's idle in the host we don't need to synchronize, unless 
> > there is an interrupt (which does its own synchronization) because
> > the idle loop has nothing valuable to leak.
> 
> Right. The only case that doesn't need synchronization is "other sibling 
> is idle in the _host_".

It still needs synchronization as you have to enforce that the other
sibling _IS_ in forced idle and not trying to do something else. Unless it
has reached forced idle state you can't vmenter.

Thanks,

	tglx

  reply	other threads:[~2018-05-27 18:57 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-24  9:06 [MODERATED] L1D-Fault KVM mitigation Joerg Roedel
2018-04-24  9:35 ` [MODERATED] " Peter Zijlstra
2018-04-24  9:48   ` David Woodhouse
2018-04-24 11:04     ` Peter Zijlstra
2018-04-24 11:16       ` David Woodhouse
2018-04-24 15:10         ` Jon Masters
2018-05-23  9:45       ` David Woodhouse
2018-05-24  9:45         ` Peter Zijlstra
2018-05-24 14:14           ` Jon Masters
2018-05-24 15:04           ` Thomas Gleixner
2018-05-24 15:33             ` Thomas Gleixner
2018-05-24 15:38               ` [MODERATED] " Jiri Kosina
2018-05-24 17:22                 ` Dave Hansen
2018-05-24 17:30                   ` Linus Torvalds
2018-05-24 23:18               ` [MODERATED] Encrypted Message Tim Chen
2018-05-24 23:28                 ` [MODERATED] Re: L1D-Fault KVM mitigation Linus Torvalds
2018-05-25  8:31                   ` Thomas Gleixner
2018-05-28 14:43                     ` [MODERATED] " Paolo Bonzini
2018-05-25 18:22                 ` [MODERATED] Encrypted Message Tim Chen
2018-05-26 19:14                 ` L1D-Fault KVM mitigation Thomas Gleixner
2018-05-26 20:43                   ` [MODERATED] " Andi Kleen
2018-05-26 20:48                     ` Linus Torvalds
2018-05-27 18:25                       ` Andi Kleen
2018-05-27 18:49                         ` Linus Torvalds
2018-05-27 18:57                           ` Thomas Gleixner [this message]
2018-05-27 19:13                           ` Andrew Cooper
2018-05-27 19:26                             ` Linus Torvalds
2018-05-27 19:41                               ` Thomas Gleixner
2018-05-27 22:26                                 ` [MODERATED] " Andrew Cooper
2018-05-28  6:47                                   ` Thomas Gleixner
2018-05-28 12:26                                     ` [MODERATED] " Andrew Cooper
2018-05-28 14:40                           ` Paolo Bonzini
2018-05-28 15:56                             ` Thomas Gleixner
2018-05-28 17:15                               ` [MODERATED] " Paolo Bonzini
2018-05-27 15:42                     ` Thomas Gleixner
2018-05-27 16:26                       ` [MODERATED] " Linus Torvalds
2018-05-27 18:31                       ` Andi Kleen
2018-05-29 19:29                   ` [MODERATED] Encrypted Message Tim Chen
2018-05-29 21:14                     ` L1D-Fault KVM mitigation Thomas Gleixner
2018-05-30 16:38                       ` [MODERATED] Encrypted Message Tim Chen
2018-05-24 15:44             ` [MODERATED] Re: L1D-Fault KVM mitigation Andi Kleen
2018-05-24 15:38           ` Linus Torvalds
2018-05-24 15:59             ` David Woodhouse
2018-05-24 16:35               ` Linus Torvalds
2018-05-24 16:51                 ` David Woodhouse
2018-05-24 16:57                   ` Linus Torvalds
2018-05-25 11:29                     ` David Woodhouse
2018-04-24 10:30   ` [MODERATED] Re: ***UNCHECKED*** " Joerg Roedel
2018-04-24 11:09     ` Thomas Gleixner
2018-04-24 16:06       ` [MODERATED] " Andi Kleen
2018-04-24 12:53   ` Paolo Bonzini
2018-05-03 16:20     ` Konrad Rzeszutek Wilk
2018-05-07 17:11       ` Paolo Bonzini
2018-05-16  8:51         ` Jiri Kosina
2018-05-16  8:53           ` Paolo Bonzini
2018-05-21 10:06             ` David Woodhouse
2018-05-21 13:40               ` Thomas Gleixner

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