linux-kernel - Re: [PATCH 0/4] KVM: arm/arm64: vgic: Use raw

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Date:   Tue, 20 Nov 2018 15:20:00 +0100
From:   Christoffer Dall <christoffer.dall@....com>
To:     Julien Thierry <julien.thierry@....com>
Cc:     linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        marc.zyngier@....com, linux-arm-kernel@...ts.infradead.org,
        linux-rt-users@...r.kernel.org, tglx@...utronix.de,
        rostedt@...dmis.org, bigeasy@...utronix.de
Subject: Re: [PATCH 0/4] KVM: arm/arm64: vgic: Use raw_spinlock for locks
 taken in IRQ context

On Mon, Nov 19, 2018 at 05:07:55PM +0000, Julien Thierry wrote:
> While testing KVM running on PREEMPT_RT, starting guest could simply
> freeze the machine. This is because we are using spinlocks for VGIC
> locks, which is invalid in the VGIC case since the locks must be take
> with interrupts disabled.
> 
> The solution is to use raw_spinlock instead of spinlocks.
> 
> Replacing those locks also highlighted an issue where we attempt to
> cond_resched with interrupts disabled.
> 
> Patch 1 fixes the cond_resched issue.

I don't agree with this fix without seeing a more thorough analysis.

> Patch 2-4 replace the VGIC spinlocks with raw_spinlocks
> 

For these:

Acked-by: Christoffer Dall <christoffer.dall@....com>



Thanks,

    Christoffer