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KVM: MIPS/Emulate: Update CP0_Compare emulation for VZ

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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@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
This commit is contained in:
James Hogan 2017-03-14 10:15:28 +00:00
parent 372582a6c6
commit 5dee99b24e
1 changed files with 42 additions and 1 deletions
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43
arch/mips/kvm/emulate.c
View File

@ -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());
}
/**