diff options
Diffstat (limited to 'debian/patches-rt/powerpc_kvm__Disable_in-kernel_MPIC_emulation_for_PREEMPT_RT.patch')
| -rw-r--r-- | debian/patches-rt/powerpc_kvm__Disable_in-kernel_MPIC_emulation_for_PREEMPT_RT.patch | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/debian/patches-rt/powerpc_kvm__Disable_in-kernel_MPIC_emulation_for_PREEMPT_RT.patch b/debian/patches-rt/powerpc_kvm__Disable_in-kernel_MPIC_emulation_for_PREEMPT_RT.patch new file mode 100644 index 000000000..f53f527b3 --- /dev/null +++ b/debian/patches-rt/powerpc_kvm__Disable_in-kernel_MPIC_emulation_for_PREEMPT_RT.patch @@ -0,0 +1,43 @@ +Subject: powerpc/kvm: Disable in-kernel MPIC emulation for PREEMPT_RT +From: Bogdan Purcareata <bogdan.purcareata@freescale.com> +Date: Fri Apr 24 15:53:13 2015 +0000 +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz + +From: Bogdan Purcareata <bogdan.purcareata@freescale.com> + +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> +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> + + +--- + arch/powerpc/kvm/Kconfig | 1 + + 1 file changed, 1 insertion(+) +--- +--- a/arch/powerpc/kvm/Kconfig ++++ b/arch/powerpc/kvm/Kconfig +@@ -224,6 +224,7 @@ config KVM_E500MC + config KVM_MPIC + bool "KVM in-kernel MPIC emulation" + depends on KVM && PPC_E500 ++ depends on !PREEMPT_RT + select HAVE_KVM_IRQCHIP + select HAVE_KVM_IRQFD + select HAVE_KVM_IRQ_ROUTING |