From: Pavel Fedin <p.fedin@samsung.com>
To: 'Marc Zyngier' <marc.zyngier@arm.com>,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: 'Ard Biesheuvel' <ard.biesheuvel@linaro.org>,
christoffer.dall@linaro.org
Subject: RE: BUG ALERT: ARM32 KVM does not work in 4.4-rc3
Date: Tue, 01 Dec 2015 15:09:24 +0300 [thread overview]
Message-ID: <015d01d12c31$1ec71c00$5c555400$@samsung.com> (raw)
In-Reply-To: <013201d12c1f$83f93250$8beb96f0$@samsung.com>
Hello!
> -----Original Message-----
> From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org] On Behalf Of Pavel Fedin
> Sent: Tuesday, December 01, 2015 1:03 PM
> To: 'Marc Zyngier'; kvmarm@lists.cs.columbia.edu; kvm@vger.kernel.org
> Cc: 'Ard Biesheuvel'; christoffer.dall@linaro.org
> Subject: RE: BUG ALERT: ARM32 KVM does not work in 4.4-rc3
>
> Hello!
>
> > > My project involves ARM64, but from time to time i also test ARM32
> > > KVM. I have discovered that it stopped working in 4.4-rc3. The same
> > > virtual machine works perfectly under current kvmarm/next, but gets
> > > stuck at random point under 4.4-rc3 from linux-stable. I'm not sure
> > > that i have time to investigate this quickly, but i'll post some new
> > > information as soon as i get it
>
> [skip]
>
> > So until you bisect it to an exact commit and configuration, I declare
> > the alert over. ;-)
>
> The commit in question is e6fab54423450d699a09ec2b899473a541f61971 ("ARM/arm64: KVM: test
> properly for a PTE's uncachedness").
> Reverting it fixes the problem.
> Study in qemu shows that the CPU gets stuck at PC = 0x0C with LR = 0x10. So i quickly decided
> that it might have to do with
> caching, and my first hit was correct. The guest crashes in this state very early, sometimes
> it even cannot fully print
> "Uncompressing kernel".
> The machine which reproduces it is custom Samsung's out-of-tree board. I'll investigate it
> further in order to determine how
> exactly the commit could harm. I know that it passed reviews and testing, and i was involved
> too. Perhaps it's board's code fault,
> however.
>
> Cc'ed to others involved.
The problem seems to be triggered by ARCH_SPARSEMEM_ENABLE. My top-secret machine uses it, while more widespread things like
vexpress and Exynos don't.
Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia
next prev parent reply other threads:[~2015-12-01 12:09 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-01 7:24 BUG ALERT: ARM32 KVM does not work in 4.4-rc3 Pavel Fedin
2015-12-01 9:25 ` Marc Zyngier
2015-12-01 9:29 ` Pavel Fedin
2015-12-01 10:03 ` Pavel Fedin
2015-12-01 12:09 ` Pavel Fedin [this message]
2015-12-02 8:19 ` Pavel Fedin
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