Re: [PATCH 23/59] KVM: arm64: nv: Respect virtual HCR_EL2.TWX setting

From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Julien Thierry <julien.thierry@arm.com>,
	Marc Zyngier <marc.zyngier@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: Andre Przywara <andre.przywara@arm.com>,
	Dave Martin <Dave.Martin@arm.com>
Subject: Re: [PATCH 23/59] KVM: arm64: nv: Respect virtual HCR_EL2.TWX setting
Date: Tue, 2 Jul 2019 13:54:34 +0100
Message-ID: <1ba3a46e-d8cd-d6c9-c1dc-2fe9ad309497@arm.com> (raw)
In-Reply-To: <53793288-0d5d-4212-c1f4-ffa6a790d1c4@arm.com>

On 6/25/19 3:19 PM, Julien Thierry wrote:
>
> On 06/21/2019 10:38 AM, Marc Zyngier wrote:
>> From: Jintack Lim <jintack.lim@linaro.org>
>>
>> Forward exceptions due to WFI or WFE instructions to the virtual EL2 if
>> they are not coming from the virtual EL2 and virtual HCR_EL2.TWX is set.
>>
>> Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>>  arch/arm64/include/asm/kvm_nested.h |  2 ++
>>  arch/arm64/kvm/Makefile             |  1 +
>>  arch/arm64/kvm/handle_exit.c        | 13 +++++++++-
>>  arch/arm64/kvm/nested.c             | 39 +++++++++++++++++++++++++++++
>>  4 files changed, 54 insertions(+), 1 deletion(-)
>>  create mode 100644 arch/arm64/kvm/nested.c
>>
>> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
>> index 8a3d121a0b42..645e5e11b749 100644
>> --- a/arch/arm64/include/asm/kvm_nested.h
>> +++ b/arch/arm64/include/asm/kvm_nested.h
>> @@ -10,4 +10,6 @@ static inline bool nested_virt_in_use(const struct kvm_vcpu *vcpu)
>>  		test_bit(KVM_ARM_VCPU_NESTED_VIRT, vcpu->arch.features);
>>  }
>>  
>> +int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe);
>> +
>>  #endif /* __ARM64_KVM_NESTED_H */
>> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
>> index 9e450aea7db6..f11bd8b0d837 100644
>> --- a/arch/arm64/kvm/Makefile
>> +++ b/arch/arm64/kvm/Makefile
>> @@ -36,4 +36,5 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/irqchip.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arch_timer.o
>>  kvm-$(CONFIG_KVM_ARM_PMU) += $(KVM)/arm/pmu.o
>>  
>> +kvm-$(CONFIG_KVM_ARM_HOST) += nested.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += emulate-nested.o
>> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
>> index e348c15c81bc..ddba212fd6ec 100644
>> --- a/arch/arm64/kvm/handle_exit.c
>> +++ b/arch/arm64/kvm/handle_exit.c
>> @@ -127,7 +127,18 @@ static int handle_no_fpsimd(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>   */
>>  static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>  {
>> -	if (kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WFx_ISS_WFE) {
>> +	bool is_wfe = !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WFx_ISS_WFE);
>> +
>> +	if (nested_virt_in_use(vcpu)) {
>> +		int ret = handle_wfx_nested(vcpu, is_wfe);
>> +
>> +		if (ret < 0 && ret != -EINVAL)
>> +			return ret;
>> +		else if (ret >= 0)
>> +			return ret;
> I think you can simplify this:
>
> 	if (ret != -EINVAL)
> 		return ret;

And handle_wfx_nested can only return -EINVAL or 1 (from
kvm_inject_nested_sync), so the condition is not only complicated, but also
misleading.

Thanks,

Alex

>
> Cheers,
>
> Julien
>
>
>> +	}
>> +
>> +	if (is_wfe) {
>>  		trace_kvm_wfx_arm64(*vcpu_pc(vcpu), true);
>>  		vcpu->stat.wfe_exit_stat++;
>>  		kvm_vcpu_on_spin(vcpu, vcpu_mode_priv(vcpu));
>> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
>> new file mode 100644
>> index 000000000000..3872e3cf1691
>> --- /dev/null
>> +++ b/arch/arm64/kvm/nested.c
>> @@ -0,0 +1,39 @@
>> +/*
>> + * Copyright (C) 2017 - Columbia University and Linaro Ltd.
>> + * Author: Jintack Lim <jintack.lim@linaro.org>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
>> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>> + */
>> +
>> +#include <linux/kvm.h>
>> +#include <linux/kvm_host.h>
>> +
>> +#include <asm/kvm_emulate.h>
>> +
>> +/*
>> + * Inject wfx to the virtual EL2 if this is not from the virtual EL2 and
>> + * the virtual HCR_EL2.TWX is set. Otherwise, let the host hypervisor
>> + * handle this.
>> + */
>> +int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe)
>> +{
>> +	u64 hcr_el2 = __vcpu_sys_reg(vcpu, HCR_EL2);
>> +
>> +	if (vcpu_mode_el2(vcpu))
>> +		return -EINVAL;
>> +
>> +	if ((is_wfe && (hcr_el2 & HCR_TWE)) || (!is_wfe && (hcr_el2 & HCR_TWI)))
>> +		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_hsr(vcpu));
>> +
>> +	return -EINVAL;
>> +}
>>
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