linux-kernel - Re: KVM patches applied in weird order in -stable

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Date:   Tue, 13 Sep 2016 16:58:09 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: KVM patches applied in weird order in -stable

[adding stable@ as this is a stable issue, not a 'normal' issue]

On Tue, Sep 13, 2016 at 03:51:00PM +0100, Matt Fleming wrote:
> Folks,
> 
> While hunting down a performance issue involving KVM I was surprised
> to see "native_set_debugreg()" as the first entry in `perf top`.
> 
> Digging deeper, it looks as though the following patches were applied
> in the wrong order in -stable. This is the order as they appear in
> Linus' tree,
> 
>  [0] commit 4e422bdd2f84 ("KVM: x86: fix missed hardware breakpoints")
>  [1] commit 172b2386ed16 ("KVM: x86: fix missed hardware breakpoints")
>  [2] commit 70e4da7a8ff6 ("KVM: x86: fix root cause for missed hardware breakpoints")
> 
> but this is the order for linux-4.4.y
> 
>  [1] commit fc90441e728a ("KVM: x86: fix missed hardware breakpoints")
>  [2] commit 25e8618619a5 ("KVM: x86: fix root cause for missed hardware breakpoints")
>  [0] commit 0f6e5e26e68f ("KVM: x86: fix missed hardware breakpoints")
> 
> The upshot is that KVM_DEBUGREG_RELOAD is always set when returning
> from kvm_arch_vcpu_load() in stable, but not in Linus' tree.

How would applying these in a different order cause breakage?

And if this is a problem, can you please send me a patch to fix it up?

thanks,

greg k-h