linux-kernel - [PATCH 4.4 005/118] Revert "KVM: x86: fix missed hardware breakpoints"

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Message-Id: <20160922172938.912741303@linuxfoundation.org>
Date:   Thu, 22 Sep 2016 19:28:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "matt@...eblueprint.co.uk, Paolo Bonzini" <pbonzini@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 4.4 005/118] Revert "KVM: x86: fix missed hardware breakpoints"

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paolo Bonzini <pbonzini@...hat.com>

[the change is part of 70e4da7a8ff62f2775337b705f45c804bb450454, which
is already in stable kernels 4.1.y to 4.4.y.  this part of the fix
however was later undone, so remove the line again]

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.

This happened because [0] and [1] are the same patch.  [0] and [1] come from two
different merges, and the later merge is trivially resolved; when [2]
is applied it reverts both of them.  Instead, when using the [1][2][0]
order, patches applies normally but "KVM: x86: fix missed hardware
breakpoints" is present in the final tree.

Reported-by: Matt Fleming <matt@...eblueprint.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kvm/x86.c |    1 -
 1 file changed, 1 deletion(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2735,7 +2735,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu
 	}

 	kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
-	vcpu->arch.switch_db_regs |= KVM_DEBUGREG_RELOAD;
 }

 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)