45 lines
1.9 KiB
Diff
45 lines
1.9 KiB
Diff
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From 640ea54850ff397aa0c2094aa2e01495296a71b5 Mon Sep 17 00:00:00 2001
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From: Bogdan Purcareata <bogdan.purcareata@freescale.com>
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Date: Fri, 24 Apr 2015 15:53:13 +0000
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Subject: [PATCH 249/365] powerpc/kvm: Disable in-kernel MPIC emulation for
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PREEMPT_RT_FULL
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While converting the openpic emulation code to use a raw_spinlock_t enables
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guests to run on RT, there's still a performance issue. For interrupts sent in
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directed delivery mode with a multiple CPU mask, the emulated openpic will loop
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through all of the VCPUs, and for each VCPUs, it call IRQ_check, which will loop
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through all the pending interrupts for that VCPU. This is done while holding the
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raw_lock, meaning that in all this time the interrupts and preemption are
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disabled on the host Linux. A malicious user app can max both these number and
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cause a DoS.
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This temporary fix is sent for two reasons. First is so that users who want to
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use the in-kernel MPIC emulation are aware of the potential latencies, thus
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making sure that the hardware MPIC and their usage scenario does not involve
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interrupts sent in directed delivery mode, and the number of possible pending
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interrupts is kept small. Secondly, this should incentivize the development of a
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proper openpic emulation that would be better suited for RT.
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Acked-by: Scott Wood <scottwood@freescale.com>
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Signed-off-by: Bogdan Purcareata <bogdan.purcareata@freescale.com>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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arch/powerpc/kvm/Kconfig | 1 +
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1 file changed, 1 insertion(+)
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diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
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index 029be26b5a17..9528089ea142 100644
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--- a/arch/powerpc/kvm/Kconfig
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+++ b/arch/powerpc/kvm/Kconfig
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@@ -175,6 +175,7 @@ config KVM_E500MC
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config KVM_MPIC
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bool "KVM in-kernel MPIC emulation"
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depends on KVM && E500
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+ depends on !PREEMPT_RT_FULL
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select HAVE_KVM_IRQCHIP
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select HAVE_KVM_IRQFD
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select HAVE_KVM_IRQ_ROUTING
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--
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2.28.0
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