4.2.8-ckt12 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: James Hogan <james.hogan@xxxxxxxxxx> commit b45bacd2d048f405c7760e5cc9b60dd67708734f upstream. Writing CP0_Compare clears the timer interrupt pending bit (CP0_Cause.TI), but this wasn't being done atomically. If a timer interrupt raced with the write of the guest CP0_Compare, the timer interrupt could end up being pending even though the new CP0_Compare is nowhere near CP0_Count. We were already updating the hrtimer expiry with kvm_mips_update_hrtimer(), which used both kvm_mips_freeze_hrtimer() and kvm_mips_resume_hrtimer(). Close the race window by expanding out kvm_mips_update_hrtimer(), and clearing CP0_Cause.TI and setting CP0_Compare between the freeze and resume. Since the pending timer interrupt should not be cleared when CP0_Compare is written via the KVM user API, an ack argument is added to distinguish the source of the write. Fixes: e30492bbe95a ("MIPS: KVM: Rewrite count/compare timer emulation") Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: "Radim KrÄmář" <rkrcmar@xxxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxx Cc: kvm@xxxxxxxxxxxxxxx Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx> --- arch/mips/include/asm/kvm_host.h | 2 +- arch/mips/kvm/emulate.c | 61 ++++++++++++++++++---------------------- arch/mips/kvm/trap_emul.c | 2 +- 3 files changed, 29 insertions(+), 36 deletions(-) diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h index e8c8d9d..4afe1ec 100644 --- a/arch/mips/include/asm/kvm_host.h +++ b/arch/mips/include/asm/kvm_host.h @@ -782,7 +782,7 @@ extern enum emulation_result kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu, uint32_t kvm_mips_read_count(struct kvm_vcpu *vcpu); void kvm_mips_write_count(struct kvm_vcpu *vcpu, uint32_t count); -void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare); +void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare, bool ack); void kvm_mips_init_count(struct kvm_vcpu *vcpu); int kvm_mips_set_count_ctl(struct kvm_vcpu *vcpu, s64 count_ctl); int kvm_mips_set_count_resume(struct kvm_vcpu *vcpu, s64 count_resume); diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c index eaf77b5..dc10c77 100644 --- a/arch/mips/kvm/emulate.c +++ b/arch/mips/kvm/emulate.c @@ -438,32 +438,6 @@ static void kvm_mips_resume_hrtimer(struct kvm_vcpu *vcpu, } /** - * kvm_mips_update_hrtimer() - Update next expiry time of hrtimer. - * @vcpu: Virtual CPU. - * - * Recalculates and updates the expiry time of the hrtimer. This can be used - * after timer parameters have been altered which do not depend on the time that - * the change occurs (in those cases kvm_mips_freeze_hrtimer() and - * kvm_mips_resume_hrtimer() are used directly). - * - * It is guaranteed that no timer interrupts will be lost in the process. - * - * Assumes !kvm_mips_count_disabled(@vcpu) (guest CP0_Count timer is running). - */ -static void kvm_mips_update_hrtimer(struct kvm_vcpu *vcpu) -{ - ktime_t now; - uint32_t count; - - /* - * freeze_hrtimer takes care of a timer interrupts <= count, and - * resume_hrtimer the hrtimer takes care of a timer interrupts > count. - */ - now = kvm_mips_freeze_hrtimer(vcpu, &count); - kvm_mips_resume_hrtimer(vcpu, now, count); -} - -/** * kvm_mips_write_count() - Modify the count and update timer. * @vcpu: Virtual CPU. * @count: Guest CP0_Count value to set. @@ -558,23 +532,42 @@ int kvm_mips_set_count_hz(struct kvm_vcpu *vcpu, s64 count_hz) * kvm_mips_write_compare() - Modify compare and update timer. * @vcpu: Virtual CPU. * @compare: New CP0_Compare value. + * @ack: Whether to acknowledge timer interrupt. * * Update CP0_Compare to a new value and update the timeout. + * If @ack, atomically acknowledge any pending timer interrupt, otherwise ensure + * any pending timer interrupt is preserved. */ -void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare) +void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare, bool ack) { struct mips_coproc *cop0 = vcpu->arch.cop0; + int dc; + u32 old_compare = kvm_read_c0_guest_compare(cop0); + ktime_t now; + uint32_t count; /* if unchanged, must just be an ack */ - if (kvm_read_c0_guest_compare(cop0) == compare) + if (old_compare == compare) { + if (!ack) + return; + kvm_mips_callbacks->dequeue_timer_int(vcpu); + kvm_write_c0_guest_compare(cop0, compare); return; + } + + /* freeze_hrtimer() takes care of timer interrupts <= count */ + dc = kvm_mips_count_disabled(vcpu); + if (!dc) + now = kvm_mips_freeze_hrtimer(vcpu, &count); + + if (ack) + kvm_mips_callbacks->dequeue_timer_int(vcpu); - /* Update compare */ kvm_write_c0_guest_compare(cop0, compare); - /* Update timeout if count enabled */ - if (!kvm_mips_count_disabled(vcpu)) - kvm_mips_update_hrtimer(vcpu); + /* resume_hrtimer() takes care of timer interrupts > count */ + if (!dc) + kvm_mips_resume_hrtimer(vcpu, now, count); } /** @@ -1113,9 +1106,9 @@ enum emulation_result kvm_mips_emulate_CP0(uint32_t inst, uint32_t *opc, /* If we are writing to COMPARE */ /* Clear pending timer interrupt, if any */ - kvm_mips_callbacks->dequeue_timer_int(vcpu); kvm_mips_write_compare(vcpu, - vcpu->arch.gprs[rt]); + vcpu->arch.gprs[rt], + true); } else if ((rd == MIPS_CP0_STATUS) && (sel == 0)) { unsigned int old_val, val, change; diff --git a/arch/mips/kvm/trap_emul.c b/arch/mips/kvm/trap_emul.c index d836ed5..307cc4c 100644 --- a/arch/mips/kvm/trap_emul.c +++ b/arch/mips/kvm/trap_emul.c @@ -547,7 +547,7 @@ static int kvm_trap_emul_set_one_reg(struct kvm_vcpu *vcpu, kvm_mips_write_count(vcpu, v); break; case KVM_REG_MIPS_CP0_COMPARE: - kvm_mips_write_compare(vcpu, v); + kvm_mips_write_compare(vcpu, v, false); break; case KVM_REG_MIPS_CP0_CAUSE: /* -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html