From 5dee99b24eeffbe673a71237faf551978cd311d3 Mon Sep 17 00:00:00 2001 From: James Hogan Date: Tue, 14 Mar 2017 10:15:28 +0000 Subject: [PATCH] KVM: MIPS/Emulate: Update CP0_Compare emulation for VZ MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: Paolo Bonzini Cc: "Radim Krčmář" Cc: Ralf Baechle Cc: linux-mips@linux-mips.org Cc: kvm@vger.kernel.org --- 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 e6fce30..4242482 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()); } /** -- 2.7.4