Re: [PATCH v5 04/10] KVM: arm64: Add vendor hypervisor firmware register

[Gavin Shan <gshan@redhat.com>]

Hi Raghavendra,

On 4/14/22 12:59 AM, Raghavendra Rao Ananta wrote:
> On Tue, Apr 12, 2022 at 8:59 PM Gavin Shan <gshan@redhat.com> wrote:
>> On 4/7/22 9:15 AM, Raghavendra Rao Ananta wrote:
>>> Introduce the firmware register to hold the vendor specific
>>> hypervisor service calls (owner value 6) as a bitmap. The
>>> bitmap represents the features that'll be enabled for the
>>> guest, as configured by the user-space. Currently, this
>>> includes support for KVM-vendor features, and Precision Time
>>> Protocol (PTP), represented by bit-0 and bit-1 respectively.
>>>
>>> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
>>> ---
>>>    arch/arm64/include/asm/kvm_host.h |  2 ++
>>>    arch/arm64/include/uapi/asm/kvm.h |  4 ++++
>>>    arch/arm64/kvm/hypercalls.c       | 21 +++++++++++++++++----
>>>    include/kvm/arm_hypercalls.h      |  4 ++++
>>>    4 files changed, 27 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>>> index 20165242ebd9..b79161bad69a 100644
>>> --- a/arch/arm64/include/asm/kvm_host.h
>>> +++ b/arch/arm64/include/asm/kvm_host.h
>>> @@ -106,10 +106,12 @@ struct kvm_arch_memory_slot {
>>>     *
>>>     * @std_bmap: Bitmap of standard secure service calls
>>>     * @std_hyp_bmap: Bitmap of standard hypervisor service calls
>>> + * @vendor_hyp_bmap: Bitmap of vendor specific hypervisor service calls
>>>     */
>>>    struct kvm_smccc_features {
>>>        u64 std_bmap;
>>>        u64 std_hyp_bmap;
>>> +     u64 vendor_hyp_bmap;
>>>    };
>>>
>>>    struct kvm_arch {
>>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
>>> index 67353bf4e69d..9a5ac0ed4113 100644
>>> --- a/arch/arm64/include/uapi/asm/kvm.h
>>> +++ b/arch/arm64/include/uapi/asm/kvm.h
>>> @@ -344,6 +344,10 @@ struct kvm_arm_copy_mte_tags {
>>>    #define KVM_REG_ARM_STD_HYP_BMAP            KVM_REG_ARM_FW_FEAT_BMAP_REG(1)
>>>    #define KVM_REG_ARM_STD_HYP_BIT_PV_TIME             BIT(0)
>>>
>>> +#define KVM_REG_ARM_VENDOR_HYP_BMAP          KVM_REG_ARM_FW_FEAT_BMAP_REG(2)
>>> +#define KVM_REG_ARM_VENDOR_HYP_BIT_FUNC_FEAT BIT(0)
>>> +#define KVM_REG_ARM_VENDOR_HYP_BIT_PTP               BIT(1)
>>> +
>>>    /* Device Control API: ARM VGIC */
>>>    #define KVM_DEV_ARM_VGIC_GRP_ADDR   0
>>>    #define KVM_DEV_ARM_VGIC_GRP_DIST_REGS      1
>>> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
>>> index 64ae6c7e7145..80836c341fd3 100644
>>> --- a/arch/arm64/kvm/hypercalls.c
>>> +++ b/arch/arm64/kvm/hypercalls.c
>>> @@ -66,8 +66,6 @@ static const u32 hvc_func_default_allowed_list[] = {
>>>        ARM_SMCCC_VERSION_FUNC_ID,
>>>        ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
>>>        ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID,
>>> -     ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID,
>>> -     ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID,
>>>    };
>>>
>>>    static bool kvm_hvc_call_default_allowed(struct kvm_vcpu *vcpu, u32 func_id)
>>> @@ -102,6 +100,12 @@ static bool kvm_hvc_call_allowed(struct kvm_vcpu *vcpu, u32 func_id)
>>>        case ARM_SMCCC_HV_PV_TIME_ST:
>>>                return kvm_arm_fw_reg_feat_enabled(smccc_feat->std_hyp_bmap,
>>>                                        KVM_REG_ARM_STD_HYP_BIT_PV_TIME);
>>> +     case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
>>> +             return kvm_arm_fw_reg_feat_enabled(smccc_feat->vendor_hyp_bmap,
>>> +                                     KVM_REG_ARM_VENDOR_HYP_BIT_FUNC_FEAT);
>>> +     case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
>>> +             return kvm_arm_fw_reg_feat_enabled(smccc_feat->vendor_hyp_bmap,
>>> +                                     KVM_REG_ARM_VENDOR_HYP_BIT_PTP);
>>>        default:
>>>                return kvm_hvc_call_default_allowed(vcpu, func_id);
>>>        }
>>
>> I guess we may return SMCCC_RET_NOT_SUPPORTED for ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID
>> if KVM_REG_ARM_VENDOR_HYP_BIT_FUNC_FEAT isn't set? Otherwise, we need explain it
>> in the commit log.
>>
> ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID is a part of the hvc
> allowed-list (hvc_func_default_allowed_list[]), which means it's not
> associated with any feature bit and is always enabled. If the guest
> were to issue ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, we'd end up in
> the 'default' case and the kvm_hvc_call_default_allowed() would return
> 'true'. This is documented in patch 2/10.
> 

I think I might not make myself clear and sorry for that. The point is
the following hvc calls should be belonging to 'Vendor Specific Hypervisor
Service', or I'm wrong. If I'm correct, VENDOR_HYP_CALL_UID_FUNC_ID
should be disallowed if bit#0 isn't set in @vendor_hyp_bmap.

     ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID
     ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID
     ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID

ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID was introduced by commit 6e085e0ac9cf
("arm/arm64: Probe for the presence of KVM hypervisor"). According to the
commit log, the identifier and supported (vendor specific) feature list
is returned by this call and ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID.
So the users depend on both calls to probe the supported features or
services. So it seems incorrect to allow ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID
even the 'Vendor Specific Hypervisor Service' is disabled and bit#0
is cleared in @vendor_hyp_bmap by users.

>> KVM_REG_ARM_VENDOR_HYP_BIT_{FUNC_FEAT, PTP} aren't parallel to each other.
>> I think PTP can't be on if KVM_REG_ARM_VENDOR_HYP_BIT_FUNC_FEAT is off.
>>
> Actually we went through this scenario [1]. Of course, we can build
> some logic around it to make sure that the userspace does the right
> thing, but at this point the consensus is that, unless it's an issue
> for KVM, it's treated as a userspace bug.
> 

Thanks for the pointer. I chime in late and I didn't check the reviewing
history on this series. Hopefully I didn't bring too much confusing comments
to you.

I think it's fine by treating it as a userspace bug, but it would be nice
to add comments somewhere if you agree.

>>> @@ -194,8 +198,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
>>>                val[3] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3;
>>>                break;
>>>        case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
>>> -             val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
>>> -             val[0] |= BIT(ARM_SMCCC_KVM_FUNC_PTP);
>>> +             val[0] = smccc_feat->vendor_hyp_bmap;
>>>                break;
>>>        case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
>>>                kvm_ptp_get_time(vcpu, val);
>>> @@ -222,6 +225,7 @@ static const u64 kvm_arm_fw_reg_ids[] = {
>>>        KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3,
>>>        KVM_REG_ARM_STD_BMAP,
>>>        KVM_REG_ARM_STD_HYP_BMAP,
>>> +     KVM_REG_ARM_VENDOR_HYP_BMAP,
>>>    };
>>>
>>>    void kvm_arm_init_hypercalls(struct kvm *kvm)
>>> @@ -230,6 +234,7 @@ void kvm_arm_init_hypercalls(struct kvm *kvm)
>>>
>>>        smccc_feat->std_bmap = KVM_ARM_SMCCC_STD_FEATURES;
>>>        smccc_feat->std_hyp_bmap = KVM_ARM_SMCCC_STD_HYP_FEATURES;
>>> +     smccc_feat->vendor_hyp_bmap = KVM_ARM_SMCCC_VENDOR_HYP_FEATURES;
>>>    }
>>>
>>>    int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
>>> @@ -322,6 +327,9 @@ int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>>        case KVM_REG_ARM_STD_HYP_BMAP:
>>>                val = READ_ONCE(smccc_feat->std_hyp_bmap);
>>>                break;
>>> +     case KVM_REG_ARM_VENDOR_HYP_BMAP:
>>> +             val = READ_ONCE(smccc_feat->vendor_hyp_bmap);
>>> +             break;
>>>        default:
>>>                return -ENOENT;
>>>        }
>>> @@ -348,6 +356,10 @@ static int kvm_arm_set_fw_reg_bmap(struct kvm_vcpu *vcpu, u64 reg_id, u64 val)
>>>                fw_reg_bmap = &smccc_feat->std_hyp_bmap;
>>>                fw_reg_features = KVM_ARM_SMCCC_STD_HYP_FEATURES;
>>>                break;
>>> +     case KVM_REG_ARM_VENDOR_HYP_BMAP:
>>> +             fw_reg_bmap = &smccc_feat->vendor_hyp_bmap;
>>> +             fw_reg_features = KVM_ARM_SMCCC_VENDOR_HYP_FEATURES;
>>> +             break;
>>>        default:
>>>                return -ENOENT;
>>>        }
>>
>> If KVM_REG_ARM_VENDOR_HYP_BIT_{FUNC_FEAT, PTP} aren't parallel to each other,
>> special code is needed to gurantee PTP is cleared if VENDOR_HYP is disabled.
>>
> Please see the above comment :)
> 

Thanks for the pointer and explanation :)

>>> @@ -453,6 +465,7 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>>                return 0;
>>>        case KVM_REG_ARM_STD_BMAP:
>>>        case KVM_REG_ARM_STD_HYP_BMAP:
>>> +     case KVM_REG_ARM_VENDOR_HYP_BMAP:
>>>                return kvm_arm_set_fw_reg_bmap(vcpu, reg->id, val);
>>>        default:
>>>                return -ENOENT;
>>> diff --git a/include/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h
>>> index b0915d8c5b81..eaf4f6b318a8 100644
>>> --- a/include/kvm/arm_hypercalls.h
>>> +++ b/include/kvm/arm_hypercalls.h
>>> @@ -9,6 +9,7 @@
>>>    /* Last valid bits of the bitmapped firmware registers */
>>>    #define KVM_REG_ARM_STD_BMAP_BIT_MAX                0
>>>    #define KVM_REG_ARM_STD_HYP_BMAP_BIT_MAX    0
>>> +#define KVM_REG_ARM_VENDOR_HYP_BMAP_BIT_MAX  1
>>>
>>>    #define KVM_ARM_SMCCC_STD_FEATURES \
>>>        GENMASK_ULL(KVM_REG_ARM_STD_BMAP_BIT_MAX, 0)
>>> @@ -16,6 +17,9 @@
>>>    #define KVM_ARM_SMCCC_STD_HYP_FEATURES \
>>>        GENMASK_ULL(KVM_REG_ARM_STD_HYP_BMAP_BIT_MAX, 0)
>>>
>>> +#define KVM_ARM_SMCCC_VENDOR_HYP_FEATURES \
>>> +     GENMASK_ULL(KVM_REG_ARM_VENDOR_HYP_BMAP_BIT_MAX, 0)
>>> +
>>>    int kvm_hvc_call_handler(struct kvm_vcpu *vcpu);
>>>
>>>    static inline u32 smccc_get_function(struct kvm_vcpu *vcpu)
>>>
>>
> 
> Thanks for the review.
> 

No worries and sorry for the late chime-in :)

> 
> [1]: https://lore.kernel.org/lkml/YjA1AzZPlPV20kMj@google.com/
> 

Thanks,
Gavin