When KVM_PREEMPT_COUNT_REPORTING is enabled, the host can use
preempt_count to determine if the guest is in a critical section,
if it also has CONFIG_KVM_HETEROGENEOUS_RT enabled, in order to
use heterogeneous RT VCPU configurations.
Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx>
---
arch/x86/Kconfig | 11 +++++++++++
arch/x86/kernel/kvm.c | 10 ++++++++++
2 files changed, 21 insertions(+)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 49270655e827..d8b62789df57 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -846,6 +846,17 @@ config PARAVIRT_TIME_ACCOUNTING
config PARAVIRT_CLOCK
bool
+config KVM_PREEMPT_COUNT_REPORTING
+ bool "KVM preempt_count reporting to the host"
+ depends on KVM_GUEST && PREEMPT_COUNT
+ default n
+ help
+ Select this option to enable KVM preempt_count reporting to the host,
+ which can be useful in cases where some VCPUs are RT and the rest
+ aren't.
+
+ If in doubt, say N here.
+
config JAILHOUSE_GUEST
bool "Jailhouse non-root cell support"
depends on X86_64 && PCI
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index a26643dc6bd6..7ec53ea3f979 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -363,6 +363,16 @@ static void kvm_guest_cpu_init(void)
if (has_steal_clock)
kvm_register_steal_time();
+
+#ifdef CONFIG_KVM_PREEMPT_COUNT_REPORTING
+ if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_COUNT)) {
+ unsigned long pa;
+
+ pa = slow_virt_to_phys(this_cpu_ptr(&__preempt_count)) |
+ KVM_MSR_ENABLED;
+ wrmsrl(MSR_KVM_PREEMPT_COUNT, pa);
+ }
+#endif
}
static void kvm_pv_disable_apf(void)
--
2.32.0.432.gabb21c7263-goog
