diff options
Diffstat (limited to 'features/rt/powerpc-kvm-Disable-in-kernel-MPIC-emulation-for-PRE.patch')
| -rw-r--r-- | features/rt/powerpc-kvm-Disable-in-kernel-MPIC-emulation-for-PRE.patch | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/features/rt/powerpc-kvm-Disable-in-kernel-MPIC-emulation-for-PRE.patch b/features/rt/powerpc-kvm-Disable-in-kernel-MPIC-emulation-for-PRE.patch new file mode 100644 index 00000000..bc6061ec --- /dev/null +++ b/features/rt/powerpc-kvm-Disable-in-kernel-MPIC-emulation-for-PRE.patch @@ -0,0 +1,44 @@ +From 4496674f6fc7117a30d0c2ea5c994c9675808e69 Mon Sep 17 00:00:00 2001 +From: Bogdan Purcareata <bogdan.purcareata@freescale.com> +Date: Fri, 24 Apr 2015 15:53:13 +0000 +Subject: [PATCH 182/191] powerpc/kvm: Disable in-kernel MPIC emulation for + PREEMPT_RT + +While converting the openpic emulation code to use a raw_spinlock_t enables +guests to run on RT, there's still a performance issue. For interrupts sent in +directed delivery mode with a multiple CPU mask, the emulated openpic will loop +through all of the VCPUs, and for each VCPUs, it call IRQ_check, which will loop +through all the pending interrupts for that VCPU. This is done while holding the +raw_lock, meaning that in all this time the interrupts and preemption are +disabled on the host Linux. A malicious user app can max both these number and +cause a DoS. + +This temporary fix is sent for two reasons. First is so that users who want to +use the in-kernel MPIC emulation are aware of the potential latencies, thus +making sure that the hardware MPIC and their usage scenario does not involve +interrupts sent in directed delivery mode, and the number of possible pending +interrupts is kept small. Secondly, this should incentivize the development of a +proper openpic emulation that would be better suited for RT. + +Acked-by: Scott Wood <scottwood@freescale.com> +Signed-off-by: Bogdan Purcareata <bogdan.purcareata@freescale.com> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + arch/powerpc/kvm/Kconfig | 1 + + 1 file changed, 1 insertion(+) + +diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig +index e45644657d49..b826174ce983 100644 +--- a/arch/powerpc/kvm/Kconfig ++++ b/arch/powerpc/kvm/Kconfig +@@ -179,6 +179,7 @@ config KVM_E500MC + config KVM_MPIC + bool "KVM in-kernel MPIC emulation" + depends on KVM && E500 ++ depends on !PREEMPT_RT + select HAVE_KVM_IRQCHIP + select HAVE_KVM_IRQFD + select HAVE_KVM_IRQ_ROUTING +-- +2.19.1 + |