Update emulation of guest writes to CP0_Compare for VZ. There are two
main differences compared to trap & emulate:
- Writing to CP0_Compare in the VZ hardware guest context acks any
pending timer, clearing CP0_Cause.TI. If we don't want an ack to take
place we must carefully restore the TI bit if it was previously set.
- Even with guest timer access disabled in CP0_GuestCtl0.GT, if the
guest CP0_Count reaches the guest CP0_Compare the timer interrupt
will assert. To prevent this we must set CP0_GTOffset to move the
guest CP0_Count out of the way of the new guest CP0_Compare, either
before or after depending on whether it is a forwards or backwards
change.
Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
---
arch/mips/kvm/emulate.c | 43 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 42 insertions(+), 1 deletion(-)
diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index e6fce30eb440..42424822898c 100644
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -621,7 +621,9 @@ void kvm_mips_write_compare(struct kvm_vcpu *vcpu, u32 compare, bool ack)
struct mips_coproc *cop0 = vcpu->arch.cop0;
int dc;
u32 old_compare = kvm_read_c0_guest_compare(cop0);
- ktime_t now;
+ s32 delta = compare - old_compare;
+ u32 cause;
+ ktime_t now = ktime_set(0, 0); /* silence bogus GCC warning */
u32 count;
/* if unchanged, must just be an ack */
@@ -633,6 +635,21 @@ void kvm_mips_write_compare(struct kvm_vcpu *vcpu, u32 compare, bool ack)
return;
}
+ /*
+ * If guest CP0_Compare moves forward, CP0_GTOffset should be adjusted
+ * too to prevent guest CP0_Count hitting guest CP0_Compare.
+ *
+ * The new GTOffset corresponds to the new value of CP0_Compare, and is
+ * set prior to it being written into the guest context. We disable
+ * preemption until the new value is written to prevent restore of a
+ * GTOffset corresponding to the old CP0_Compare value.
+ */
+ if (IS_ENABLED(CONFIG_KVM_MIPS_VZ) && delta > 0) {
+ preempt_disable();
+ write_c0_gtoffset(compare - read_c0_count());
+ back_to_back_c0_hazard();
+ }
+
/* freeze_hrtimer() takes care of timer interrupts <= count */
dc = kvm_mips_count_disabled(vcpu);
if (!dc)
@@ -640,12 +657,36 @@ void kvm_mips_write_compare(struct kvm_vcpu *vcpu, u32 compare, bool ack)
if (ack)
kvm_mips_callbacks->dequeue_timer_int(vcpu);
+ else if (IS_ENABLED(CONFIG_KVM_MIPS_VZ))
+ /*
+ * With VZ, writing CP0_Compare acks (clears) CP0_Cause.TI, so
+ * preserve guest CP0_Cause.TI if we don't want to ack it.
+ */
+ cause = kvm_read_c0_guest_cause(cop0);
kvm_write_c0_guest_compare(cop0, compare);
+ if (IS_ENABLED(CONFIG_KVM_MIPS_VZ)) {
+ if (delta > 0)
+ preempt_enable();
+
+ back_to_back_c0_hazard();
+
+ if (!ack && cause & CAUSEF_TI)
+ kvm_write_c0_guest_cause(cop0, cause);
+ }
+
/* resume_hrtimer() takes care of timer interrupts > count */
if (!dc)
kvm_mips_resume_hrtimer(vcpu, now, count);
+
+ /*
+ * If guest CP0_Compare is moving backward, we delay CP0_GTOffset change
+ * until after the new CP0_Compare is written, otherwise new guest
+ * CP0_Count could hit new guest CP0_Compare.
+ */
+ if (IS_ENABLED(CONFIG_KVM_MIPS_VZ) && delta <= 0)
+ write_c0_gtoffset(compare - read_c0_count());
}
/**
--
git-series 0.8.10
