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From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Eric Auger <eric.auger@redhat.com>,
	eric.auger.pro@gmail.com, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
	maz@kernel.org, drjones@redhat.com
Cc: james.morse@arm.com, julien.thierry.kdev@gmail.com,
	suzuki.poulose@arm.com, shuah@kernel.org, pbonzini@redhat.com
Subject: Re: [PATCH 5/9] KVM: arm: move has_run_once after the map_resources
Date: Tue, 12 Jan 2021 14:55:49 +0000	[thread overview]
Message-ID: <0c9976a3-12ae-29b2-1f26-06ee52aa2ffe@arm.com> (raw)
In-Reply-To: <20201212185010.26579-6-eric.auger@redhat.com>

Hi Eric,

On 12/12/20 6:50 PM, Eric Auger wrote:
> has_run_once is set to true at the beginning of
> kvm_vcpu_first_run_init(). This generally is not an issue
> except when exercising the code with KVM selftests. Indeed,
> if kvm_vgic_map_resources() fails due to erroneous user settings,
> has_run_once is set and this prevents from continuing
> executing the test. This patch moves the assignment after the
> kvm_vgic_map_resources().
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
>  arch/arm64/kvm/arm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index c0ffb019ca8b..331fae6bff31 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -540,8 +540,6 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
>  	if (!kvm_arm_vcpu_is_finalized(vcpu))
>  		return -EPERM;
>  
> -	vcpu->arch.has_run_once = true;
> -
>  	if (likely(irqchip_in_kernel(kvm))) {
>  		/*
>  		 * Map the VGIC hardware resources before running a vcpu the
> @@ -560,6 +558,8 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
>  		static_branch_inc(&userspace_irqchip_in_use);
>  	}
>  
> +	vcpu->arch.has_run_once = true;

I have a few concerns regarding this:

1. Moving has_run_once = true here seems very arbitrary to me - kvm_timer_enable()
and kvm_arm_pmu_v3_enable(), below it, can both fail because of erroneous user
values. If there's a reason why the assignment cannot be moved at the end of the
function, I think it should be clearly stated in a comment for the people who
might be tempted to write similar tests for the timer or pmu.

2. There are many ways that kvm_vgic_map_resources() can fail, other than
incorrect user settings. I started digging into how
kvm_vgic_map_resources()->vgic_v2_map_resources() can fail for a VGIC V2 and this
is what I managed to find before I gave up:

* vgic_init() can fail in:
    - kvm_vgic_dist_init()
    - vgic_v3_init()
    - kvm_vgic_setup_default_irq_routing()
* vgic_register_dist_iodev() can fail in:
    - vgic_v3_init_dist_iodev()
    - kvm_io_bus_register_dev()(*)
* kvm_phys_addr_ioremap() can fail in:
    - kvm_mmu_topup_memory_cache()
    - kvm_pgtable_stage2_map()

So if any of the functions below fail, are we 100% sure it is safe to allow the
user to execute kvm_vgic_map_resources() again?

(*) It looks to me like kvm_io_bus_register_dev() doesn't take into account a
caller that tries to register the same device address range and it will create
another identical range. Is this intentional? Is it a bug that should be fixed? Or
am I misunderstanding the function?

Thanks,
Alex
> +
>  	ret = kvm_timer_enable(vcpu);
>  	if (ret)
>  		return ret;

  reply	other threads:[~2021-01-12 14:56 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-12 18:50 [PATCH 0/9] KVM/ARM: Some vgic fixes and init sequence KVM selftests Eric Auger
2020-12-12 18:50 ` [PATCH 1/9] KVM: arm64: vgic-v3: Fix some error codes when setting RDIST base Eric Auger
2021-01-06 16:32   ` Alexandru Elisei
2021-01-14 10:02     ` Auger Eric
2020-12-12 18:50 ` [PATCH 2/9] KVM: arm64: Fix KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION read Eric Auger
2021-01-06 17:12   ` Alexandru Elisei
2021-01-13 17:18     ` Auger Eric
2020-12-12 18:50 ` [PATCH 3/9] KVM: arm64: vgic-v3: Fix error handling in vgic_v3_set_redist_base() Eric Auger
2020-12-28 15:35   ` Marc Zyngier
2021-01-13 17:18     ` Auger Eric
2020-12-12 18:50 ` [PATCH 4/9] KVM: arm/arm64: vgic: Reset base address on kvm_vgic_dist_destroy() Eric Auger
2020-12-28 15:41   ` Marc Zyngier
2021-01-13 17:18     ` Auger Eric
2020-12-12 18:50 ` [PATCH 5/9] KVM: arm: move has_run_once after the map_resources Eric Auger
2021-01-12 14:55   ` Alexandru Elisei [this message]
2021-01-14 10:02     ` Auger Eric
2021-01-20 15:56       ` Alexandru Elisei
2021-03-12 17:27         ` Auger Eric
2020-12-12 18:50 ` [PATCH 6/9] docs: kvm: devices/arm-vgic-v3: enhance KVM_DEV_ARM_VGIC_CTRL_INIT doc Eric Auger
2021-01-12 15:39   ` Alexandru Elisei
2021-01-13 17:18     ` Auger Eric
2020-12-12 18:50 ` [PATCH 7/9] KVM: arm64: Simplify argument passing to vgic_uaccess_[read|write] Eric Auger
2021-01-12 16:04   ` Alexandru Elisei
2021-01-12 16:16     ` Alexandru Elisei
2021-01-13 17:18       ` Auger Eric
2020-12-12 18:50 ` [PATCH 8/9] KVM: arm64: vgic-v3: Expose GICR_TYPER.Last for userspace Eric Auger
2021-01-12 17:02   ` Alexandru Elisei
2021-01-14 10:16     ` Auger Eric
2021-01-20 16:13       ` Alexandru Elisei
2021-03-12 17:26         ` Auger Eric
2021-01-12 17:28   ` Alexandru Elisei
2021-01-12 17:48     ` Marc Zyngier
2020-12-12 18:50 ` [PATCH 9/9] KVM: selftests: aarch64/vgic-v3 init sequence tests Eric Auger

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