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From: Borislav Petkov <bp@alien8.de>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Jane Malalane <jane.malalane@citrix.com>,
	LKML <linux-kernel@vger.kernel.org>,
	x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Pu Wen <puwen@hygon.cn>, Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Yazen Ghannam <Yazen.Ghannam@amd.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Huang Rui <ray.huang@amd.com>, Andy Lutomirski <luto@kernel.org>,
	Kim Phillips <kim.phillips@amd.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH] x86/cpu: Fix migration safety with X86_BUG_NULL_SEL
Date: Wed, 6 Oct 2021 16:30:46 +0200	[thread overview]
Message-ID: <YV2zFlaLvZzNPkjh@zn.tnic> (raw)
In-Reply-To: <c2d96a84-64d2-b4b4-261d-e98612552ba0@citrix.com>

On Wed, Oct 06, 2021 at 03:15:51PM +0100, Andrew Cooper wrote:
> The case which goes wrong is this:
> 
> 1. Zen1 (or earlier) and Zen2 (or later) in a migration pool
> 2. Linux boots on Zen2, probes and finds the absence of X86_BUG_NULL_SEL
> 3. Linux is then migrated to Zen1
> 
> Linux is now running on a X86_BUG_NULL_SEL-impacted CPU while believing
> that the bug is fixed.
> 
> The only way to address the problem is to fully trust the "no longer
> affected" CPUID bit when virtualised, because in the above case it would
> be clear deliberately to indicate the fact "you might migrate to
> somewhere which really is affected".

Yap, makes sense.

Thanks for taking the time - that's what I was looking for.

Please add to the commit message of the next version.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2021-10-06 14:30 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-01 13:33 Jane Malalane
2021-10-01 14:07 ` Andrew Cooper
2021-10-01 14:19 ` Borislav Petkov
2021-10-06 14:15   ` Andrew Cooper
2021-10-06 14:30     ` Borislav Petkov [this message]
2021-10-05 20:58 ` Andy Lutomirski

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