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Message-ID: <20211007142239.4ryz4thzgpilphya@gator>
Date: Thu, 7 Oct 2021 16:22:39 +0200
From: Andrew Jones <drjones@...hat.com>
To: Marc Zyngier <maz@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org, will@...nel.org,
qperret@...gle.com, dbrazdil@...gle.com,
Steven Price <steven.price@....com>,
Fuad Tabba <tabba@...gle.com>,
Srivatsa Vaddagiri <vatsa@...eaurora.org>,
Shanker R Donthineni <sdonthineni@...dia.com>,
James Morse <james.morse@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
kernel-team@...roid.com
Subject: Re: [PATCH v2 09/16] KVM: arm64: Advertise a capability for MMIO
guard
On Mon, Oct 04, 2021 at 06:48:42PM +0100, Marc Zyngier wrote:
> In order for userspace to find out whether the MMIO guard is
> exposed to a guest, expose a capability that says so.
>
> We take this opportunity to make it incompatible with the NISV
> option, as that would be rather counter-productive!
>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
> arch/arm64/kvm/arm.c | 29 ++++++++++++++++++-----------
> arch/arm64/kvm/hypercalls.c | 14 ++++++++++++--
> include/uapi/linux/kvm.h | 1 +
> 3 files changed, 31 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index ed9c89ec0b4f..1c9a7abe2728 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -81,32 +81,33 @@ int kvm_arch_check_processor_compat(void *opaque)
> int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> struct kvm_enable_cap *cap)
> {
> - int r;
> + int r = -EINVAL;
>
> if (cap->flags)
> return -EINVAL;
>
> + mutex_lock(&kvm->lock);
> +
> switch (cap->cap) {
> case KVM_CAP_ARM_NISV_TO_USER:
> - r = 0;
> - set_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
> - &kvm->arch.flags);
> + /* This is incompatible with MMIO guard */
> + if (!test_bit(KVM_ARCH_FLAG_MMIO_GUARD, &kvm->arch.flags)) {
But KVM_ARCH_FLAG_MMIO_GUARD will never be set at VM creation time, which
is the traditional time to probe and enable capabilities, because the
guest hasn't run yet, so it hasn't had a chance to issue the hypercall to
enable the mmio guard yet.
> + r = 0;
> + set_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
> + &kvm->arch.flags);
> + }
> break;
> case KVM_CAP_ARM_MTE:
> - mutex_lock(&kvm->lock);
> - if (!system_supports_mte() || kvm->created_vcpus) {
> - r = -EINVAL;
> - } else {
> + if (system_supports_mte() && !kvm->created_vcpus) {
> r = 0;
> set_bit(KVM_ARCH_FLAG_MTE_ENABLED, &kvm->arch.flags);
> }
> - mutex_unlock(&kvm->lock);
> break;
> default:
> - r = -EINVAL;
> break;
> }
>
> + mutex_unlock(&kvm->lock);
> return r;
> }
>
> @@ -211,13 +212,19 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_IMMEDIATE_EXIT:
> case KVM_CAP_VCPU_EVENTS:
> case KVM_CAP_ARM_IRQ_LINE_LAYOUT_2:
> - case KVM_CAP_ARM_NISV_TO_USER:
> case KVM_CAP_ARM_INJECT_EXT_DABT:
> case KVM_CAP_SET_GUEST_DEBUG:
> case KVM_CAP_VCPU_ATTRIBUTES:
> case KVM_CAP_PTP_KVM:
> r = 1;
> break;
> + case KVM_CAP_ARM_NISV_TO_USER:
> + r = !test_bit(KVM_ARCH_FLAG_MMIO_GUARD, &kvm->arch.flags);
> + break;
> + case KVM_CAP_ARM_MMIO_GUARD:
> + r = !test_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
> + &kvm->arch.flags);
> + break;
> case KVM_CAP_SET_GUEST_DEBUG2:
> return KVM_GUESTDBG_VALID_MASK;
> case KVM_CAP_ARM_SET_DEVICE_ADDR:
> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> index c39aab55ecae..e4fade6a96f6 100644
> --- a/arch/arm64/kvm/hypercalls.c
> +++ b/arch/arm64/kvm/hypercalls.c
> @@ -59,6 +59,14 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
> val[3] = lower_32_bits(cycles);
> }
>
> +static bool mmio_guard_allowed(struct kvm_vcpu *vcpu)
> +{
> + return (!test_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
> + &vcpu->kvm->arch.flags) &&
> + !vcpu_mode_is_32bit(vcpu));
> +
> +}
> +
> int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> {
> u32 func_id = smccc_get_function(vcpu);
> @@ -131,7 +139,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
> val[0] |= BIT(ARM_SMCCC_KVM_FUNC_PTP);
> /* Only advertise MMIO guard to 64bit guests */
> - if (!vcpu_mode_is_32bit(vcpu)) {
> + if (mmio_guard_allowed(vcpu)) {
> val[0] |= BIT(ARM_SMCCC_KVM_FUNC_MMIO_GUARD_INFO);
> val[0] |= BIT(ARM_SMCCC_KVM_FUNC_MMIO_GUARD_ENROLL);
> val[0] |= BIT(ARM_SMCCC_KVM_FUNC_MMIO_GUARD_MAP);
> @@ -146,10 +154,12 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> val[0] = PAGE_SIZE;
> break;
> case ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_ENROLL_FUNC_ID:
> - if (!vcpu_mode_is_32bit(vcpu)) {
> + mutex_lock(&vcpu->kvm->lock);
> + if (mmio_guard_allowed(vcpu)) {
> set_bit(KVM_ARCH_FLAG_MMIO_GUARD, &vcpu->kvm->arch.flags);
> val[0] = SMCCC_RET_SUCCESS;
> }
> + mutex_unlock(&vcpu->kvm->lock);
> break;
> case ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_MAP_FUNC_ID:
> if (!vcpu_mode_is_32bit(vcpu) &&
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index a067410ebea5..ef171186e7be 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1112,6 +1112,7 @@ struct kvm_ppc_resize_hpt {
> #define KVM_CAP_BINARY_STATS_FD 203
> #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
> #define KVM_CAP_ARM_MTE 205
> +#define KVM_CAP_ARM_MMIO_GUARD 206
>
> #ifdef KVM_CAP_IRQ_ROUTING
>
> --
> 2.30.2
>
Thanks,
drew
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