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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hibSr-0007H1-Bj; Wed, 03 Jul 2019 09:22:09 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hibSn-0007Gg-L0 for linux-arm-kernel@lists.infradead.org; Wed, 03 Jul 2019 09:22:07 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BE9D7344; Wed, 3 Jul 2019 02:21:59 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E3DEE3F246; Wed, 3 Jul 2019 02:21:58 -0700 (PDT) Subject: Re: [PATCH 06/59] KVM: arm64: nv: Allow userspace to set PSR_MODE_EL2x To: Dave Martin References: <20190621093843.220980-1-marc.zyngier@arm.com> <20190621093843.220980-7-marc.zyngier@arm.com> <7f8a9d76-6087-b8d9-3571-074a08d08ec8@arm.com> <3a68e4e6-878f-7272-4e2d-8768680287fd@arm.com> <20190624124859.GP2790@e103592.cambridge.arm.com> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190624124859.GP2790@e103592.cambridge.arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190703_022205_777353_5E951985 X-CRM114-Status: GOOD ( 18.58 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, Andre Przywara , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Julien Thierry Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 24/06/2019 13:48, Dave Martin wrote: > On Fri, Jun 21, 2019 at 02:50:08PM +0100, Marc Zyngier wrote: >> On 21/06/2019 14:24, Julien Thierry wrote: >>> >>> >>> On 21/06/2019 10:37, Marc Zyngier wrote: >>>> From: Christoffer Dall >>>> >>>> We were not allowing userspace to set a more privileged mode for the VCPU >>>> than EL1, but we should allow this when nested virtualization is enabled >>>> for the VCPU. >>>> >>>> Signed-off-by: Christoffer Dall >>>> Signed-off-by: Marc Zyngier >>>> --- >>>> arch/arm64/kvm/guest.c | 6 ++++++ >>>> 1 file changed, 6 insertions(+) >>>> >>>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c >>>> index 3ae2f82fca46..4c35b5d51e21 100644 >>>> --- a/arch/arm64/kvm/guest.c >>>> +++ b/arch/arm64/kvm/guest.c >>>> @@ -37,6 +37,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> #include >>>> >>>> #include "trace.h" >>>> @@ -194,6 +195,11 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg) >>>> if (vcpu_el1_is_32bit(vcpu)) >>>> return -EINVAL; >>>> break; >>>> + case PSR_MODE_EL2h: >>>> + case PSR_MODE_EL2t: >>>> + if (vcpu_el1_is_32bit(vcpu) || !nested_virt_in_use(vcpu)) >>> >>> This condition reads a bit weirdly. Why do we care about anything else >>> than !nested_virt_in_use() ? >>> >>> If nested virt is not in use then obviously we return the error. >>> >>> If nested virt is in use then why do we care about EL1? Or should this >>> test read as "highest_el_is_32bit" ? >> >> There are multiple things at play here: >> >> - MODE_EL2x is not a valid 32bit mode >> - The architecture forbids nested virt with 32bit EL2 >> >> The code above is a simplification of these two conditions. But >> certainly we can do a bit better, as kvm_reset_cpu() doesn't really >> check that we don't create a vcpu with both 32bit+NV. These two bits >> should really be exclusive. > > This code is safe for now because KVM_VCPU_MAX_FEATURES <= > KVM_ARM_VCPU_NESTED_VIRT, right, i.e., nested_virt_in_use() cannot be > true? > > This makes me a little uneasy, but I think that's paranoia talking: we > want bisectably, but no sane person should ship with just half of this > series. So I guess this is fine. > > We could stick something like > > if (WARN_ON(...)) > return false; > > in nested_virt_in_use() and then remove it in the final patch, but it's > probably overkill. The only case I can imagine something going wrong is if this series is only applied halfway, and another series bumps the maximum feature to something that includes NV. I guess your suggestion would solve that. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel