KVM: MIPS/VZ: Support hardware guest timer

Transfer timer state to the VZ guest context (CP0_GTOffset & guest
CP0_Count) when entering guest mode, enabling direct guest access to it,
and transfer back to soft timer when saving guest register state.

This usually allows guest code to directly read CP0_Count (via MFC0 and
RDHWR) and read/write CP0_Compare, without trapping to the hypervisor
for it to emulate the guest timer. Writing to CP0_Count or CP0_Cause.DC
is much less common and still triggers a hypervisor GPSI exception, in
which case the timer state is transferred back to an hrtimer before
emulating the write.

We are careful to prevent small amounts of drift from building up due to
undeterministic time intervals between reading of the ktime and reading
of CP0_Count. Some drift is expected however, since the system
clocksource may use a different timer to the local CP0_Count timer used
by VZ. This is permitted to prevent guest CP0_Count from appearing to go
backwards.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org

1 files changed, 14 insertions, 0 deletions

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index a662a80152b1..5c518c148f9d 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -1068,6 +1068,20 @@ void kvm_mips_count_enable_cause(struct kvm_vcpu *vcpu);
 void kvm_mips_count_disable_cause(struct kvm_vcpu *vcpu);
 enum hrtimer_restart kvm_mips_count_timeout(struct kvm_vcpu *vcpu);
 
+/* fairly internal functions requiring some care to use */
+int kvm_mips_count_disabled(struct kvm_vcpu *vcpu);
+ktime_t kvm_mips_freeze_hrtimer(struct kvm_vcpu *vcpu, u32 *count);
+int kvm_mips_restore_hrtimer(struct kvm_vcpu *vcpu, ktime_t before,
+			     u32 count, int min_drift);
+
+#ifdef CONFIG_KVM_MIPS_VZ
+void kvm_vz_acquire_htimer(struct kvm_vcpu *vcpu);
+void kvm_vz_lose_htimer(struct kvm_vcpu *vcpu);
+#else
+static inline void kvm_vz_acquire_htimer(struct kvm_vcpu *vcpu) {}
+static inline void kvm_vz_lose_htimer(struct kvm_vcpu *vcpu) {}
+#endif
+
 enum emulation_result kvm_mips_check_privilege(u32 cause,
 					       u32 *opc,
 					       struct kvm_run *run,