linux-kernel - [PATCH 5/9] KVM: VMX: clamp PLE window

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Date:	Tue, 19 Aug 2014 22:35:32 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	kvm@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Gleb Natapov <gleb@...nel.org>,
	Raghavendra KT <raghavendra.kt@...ux.vnet.ibm.com>,
	Vinod Chegu <chegu_vinod@...com>, Hui-Zhi <hui-zhi.zhao@...com>
Subject: [PATCH 5/9] KVM: VMX: clamp PLE window

Modifications could get unwanted values of PLE window. (low or negative)
Use ple_window and the maximal value that cannot overflow as bounds.

ple_window_max defaults to a very high value, but it would make sense to
set it to some fraction of the scheduler tick.

Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
---
 arch/x86/kvm/vmx.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 66259fd..e1192fb 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -144,6 +144,10 @@ module_param(ple_window_grow, int, S_IRUGO);
 static int ple_window_shrink = KVM_VMX_DEFAULT_PLE_WINDOW_SHRINK;
 module_param(ple_window_shrink, int, S_IRUGO);
 
+/* Default is to compute the maximum so we can never overflow. */
+static int ple_window_max = INT_MAX / KVM_VMX_DEFAULT_PLE_WINDOW_GROW;
+module_param(ple_window_max, int, S_IRUGO);
+
 extern const ulong vmx_return;
 
 #define NR_AUTOLOAD_MSRS 8
@@ -5704,7 +5708,7 @@ static void grow_ple_window(struct kvm_vcpu *vcpu)
 	else
 		new = old + ple_window_grow;
 
-	vmx->ple_window = new;
+	vmx->ple_window = min(new, ple_window_max);
 }
 
 static void shrink_ple_window(struct kvm_vcpu *vcpu)
@@ -5720,7 +5724,7 @@ static void shrink_ple_window(struct kvm_vcpu *vcpu)
 	else
 		new = old - ple_window_shrink;
 
-	vmx->ple_window = new;
+	vmx->ple_window = max(new, ple_window);
 }
 
 /*
-- 
2.0.4

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