Re: [PATCH v2 07/43] arm64: RME: Check for RME support at KVM init

Steven Price
2024-04-22T15:39:34Z

On 16/04/2024 14:30, Suzuki K Poulose wrote:
> Hi Steven
>
> On 12/04/2024 09:42, Steven Price wrote:
>> Query the RMI version number and check if it is a compatible version. A
>> static key is also provided to signal that a supported RMM is available.
>>
>> Functions are provided to query if a VM or VCPU is a realm (or rec)
>> which currently will always return false.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>>   arch/arm64/include/asm/kvm_emulate.h | 18 +++++++++
>>   arch/arm64/include/asm/kvm_host.h    |  4 ++
>>   arch/arm64/include/asm/kvm_rme.h     | 56 ++++++++++++++++++++++++++++
>>   arch/arm64/include/asm/virt.h        |  1 +
>>   arch/arm64/kvm/Makefile              |  3 +-
>>   arch/arm64/kvm/arm.c                 |  9 +++++
>>   arch/arm64/kvm/rme.c                 | 52 ++++++++++++++++++++++++++
>>   7 files changed, 142 insertions(+), 1 deletion(-)
>>   create mode 100644 arch/arm64/include/asm/kvm_rme.h
>>   create mode 100644 arch/arm64/kvm/rme.c
>>
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h
>> b/arch/arm64/include/asm/kvm_emulate.h
>> index 975af30af31f..6f08398537e2 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -611,4 +611,22 @@ static __always_inline void
>> kvm_reset_cptr_el2(struct kvm_vcpu *vcpu)
>>         kvm_write_cptr_el2(val);
>>   }
>> +
>> +static inline bool kvm_is_realm(struct kvm *kvm)
>> +{
>> +    if (static_branch_unlikely(&kvm_rme_is_available))
>> +        return kvm->arch.is_realm;
>> +    return false;
>> +}
>> +
>> +static inline enum realm_state kvm_realm_state(struct kvm *kvm)
>> +{
>> +    return READ_ONCE(kvm->arch.realm.state);
>> +}
>> +
>> +static inline bool vcpu_is_rec(struct kvm_vcpu *vcpu)
>> +{
>> +    return false;
>> +}
>> +
>>   #endif /* __ARM64_KVM_EMULATE_H__ */
>> diff --git a/arch/arm64/include/asm/kvm_host.h
>> b/arch/arm64/include/asm/kvm_host.h
>> index 9e8a496fb284..63b68b85db3f 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -27,6 +27,7 @@
>>   #include <asm/fpsimd.h>
>>   #include <asm/kvm.h>
>>   #include <asm/kvm_asm.h>
>> +#include <asm/kvm_rme.h>
>>   #include <asm/vncr_mapping.h>
>>     #define __KVM_HAVE_ARCH_INTC_INITIALIZED
>> @@ -348,6 +349,9 @@ struct kvm_arch {
>>        * the associated pKVM instance in the hypervisor.
>>        */
>>       struct kvm_protected_vm pkvm;
>> +
>> +    bool is_realm;
>> +    struct realm realm;
>>   };
>>     struct kvm_vcpu_fault_info {
>> diff --git a/arch/arm64/include/asm/kvm_rme.h
>> b/arch/arm64/include/asm/kvm_rme.h
>> new file mode 100644
>> index 000000000000..922da3f47227
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/kvm_rme.h
>> @@ -0,0 +1,56 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Copyright (C) 2023 ARM Ltd.
>> + */
>> +
>> +#ifndef __ASM_KVM_RME_H
>> +#define __ASM_KVM_RME_H
>> +
>> +/**
>> + * enum realm_state - State of a Realm
>> + */
>> +enum realm_state {
>> +    /**
>> +     * @REALM_STATE_NONE:
>> +     *      Realm has not yet been created. rmi_realm_create() may be
>> +     *      called to create the realm.
>> +     */
>> +    REALM_STATE_NONE,
>> +    /**
>> +     * @REALM_STATE_NEW:
>> +     *      Realm is under construction, not eligible for execution.
>> Pages
>> +     *      may be populated with rmi_data_create().
>> +     */
>> +    REALM_STATE_NEW,
>> +    /**
>> +     * @REALM_STATE_ACTIVE:
>> +     *      Realm has been created and is eligible for execution with
>> +     *      rmi_rec_enter(). Pages may no longer be populated with
>> +     *      rmi_data_create().
>> +     */
>> +    REALM_STATE_ACTIVE,
>> +    /**
>> +     * @REALM_STATE_DYING:
>> +     *      Realm is in the process of being destroyed or has already
>> been
>> +     *      destroyed.
>> +     */
>> +    REALM_STATE_DYING,
>> +    /**
>> +     * @REALM_STATE_DEAD:
>> +     *      Realm has been destroyed.
>> +     */
>> +    REALM_STATE_DEAD
>> +};
>> +
>> +/**
>> + * struct realm - Additional per VM data for a Realm
>> + *
>> + * @state: The lifetime state machine for the realm
>> + */
>> +struct realm {
>> +    enum realm_state state;
>> +};
>> +
>> +int kvm_init_rme(void);
>> +
>> +#endif
>> diff --git a/arch/arm64/include/asm/virt.h
>> b/arch/arm64/include/asm/virt.h
>> index 261d6e9df2e1..12cf36c38189 100644
>> --- a/arch/arm64/include/asm/virt.h
>> +++ b/arch/arm64/include/asm/virt.h
>> @@ -81,6 +81,7 @@ void __hyp_reset_vectors(void);
>>   bool is_kvm_arm_initialised(void);
>>     DECLARE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
>> +DECLARE_STATIC_KEY_FALSE(kvm_rme_is_available);
>>     /* Reports the availability of HYP mode */
>>   static inline bool is_hyp_mode_available(void)
>> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
>> index c0c050e53157..1c1d8cdf381f 100644
>> --- a/arch/arm64/kvm/Makefile
>> +++ b/arch/arm64/kvm/Makefile
>> @@ -20,7 +20,8 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o
>> pvtime.o \
>>        vgic/vgic-v3.o vgic/vgic-v4.o \
>>        vgic/vgic-mmio.o vgic/vgic-mmio-v2.o \
>>        vgic/vgic-mmio-v3.o vgic/vgic-kvm-device.o \
>> -     vgic/vgic-its.o vgic/vgic-debug.o
>> +     vgic/vgic-its.o vgic/vgic-debug.o \
>> +     rme.o
>>     kvm-$(CONFIG_HW_PERF_EVENTS)  += pmu-emul.o pmu.o
>>   diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index 3dee5490eea9..2056c660c5ee 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -38,6 +38,7 @@
>>   #include <asm/kvm_mmu.h>
>>   #include <asm/kvm_nested.h>
>>   #include <asm/kvm_pkvm.h>
>> +#include <asm/kvm_rme.h>
>>   #include <asm/kvm_emulate.h>
>>   #include <asm/sections.h>
>>   @@ -47,6 +48,8 @@
>>     static enum kvm_mode kvm_mode = KVM_MODE_DEFAULT;
>>   +DEFINE_STATIC_KEY_FALSE(kvm_rme_is_available);
>> +
>>   DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
>>     DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
>> @@ -2562,6 +2565,12 @@ static __init int kvm_arm_init(void)
>>         in_hyp_mode = is_kernel_in_hyp_mode();
>>   +    if (in_hyp_mode) {
>> +        err = kvm_init_rme();
>> +        if (err)
>> +            return err;
>> +    }
>> +
>>       if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
>>           cpus_have_final_cap(ARM64_WORKAROUND_1508412))
>>           kvm_info("Guests without required CPU erratum workarounds
>> can deadlock system!\n" \
>> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
>> new file mode 100644
>> index 000000000000..3dbbf9d046bf
>> --- /dev/null
>> +++ b/arch/arm64/kvm/rme.c
>> @@ -0,0 +1,52 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2023 ARM Ltd.
>> + */
>> +
>> +#include <linux/kvm_host.h>
>> +
>> +#include <asm/rmi_cmds.h>
>> +#include <asm/virt.h>
>> +
>> +static int rmi_check_version(void)
>> +{
>> +    struct arm_smccc_res res;
>> +    int version_major, version_minor;
>> +    unsigned long host_version = RMI_ABI_VERSION(RMI_ABI_MAJOR_VERSION,
>> +                             RMI_ABI_MINOR_VERSION);
>> +
>> +    arm_smccc_1_1_invoke(SMC_RMI_VERSION, host_version, &res);
>> +
>> +    if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
>> +        return -ENXIO;
>> +
>> +    version_major = RMI_ABI_VERSION_GET_MAJOR(res.a1);
>> +    version_minor = RMI_ABI_VERSION_GET_MINOR(res.a1);
>> +
>
> We don't seem to be using the res.a0 to determin if the RMM supports our
> requested version. As per RMM spec, section B4.3.23 :
>
> "
> The status code and lower revision output values indicate which of the
> following is true, in order of precedence:
>  a) The RMM supports an interface revision which is compatible with the
>     requested revision.
>      • The status code is RMI_SUCCESS.
>      • The lower revision is equal to the requested revision.
>  b) The RMM does not support an interface revision which is compatible
>     with the requested revision The RMM supports an interface revision
>     which is incompatible with and less than the requested revision.
>      • The status code is RMI_ERROR_INPUT.
>      • The lower revision is the highest interface revision which is
>        both less than the requested revision and supported by the RMM.
>
>  c) The RMM does not support an interface revision which is compatible
>     with the requested revision The RMM supports an interface revision
>     which is incompatible with and greater than the requested revision.
>      • The status code is RMI_ERROR_INPUT.
>      • The lower revision is equal to the higher revision.
>
> So, we could simply check the res.a0 for RMI_SUCCESS and proceed with
> marking RMM available.

Good point - this didn't work in a previous version of the spec, but we
should be able to rely on the return value now.

>> +    if (version_major != RMI_ABI_MAJOR_VERSION) {
>> +        kvm_err("Unsupported RMI ABI (v%d.%d) host supports v%d.%d\n",
>> +            version_major, version_minor,
>> +            RMI_ABI_MAJOR_VERSION,
>> +            RMI_ABI_MINOR_VERSION);
>> +        return -ENXIO;
>> +    }
>> +
>> +    kvm_info("RMI ABI version %d.%d\n", version_major, version_minor);
>> +
>> +    return 0;
>> +}
>> +
>> +int kvm_init_rme(void)
>> +{
>> +    if (PAGE_SIZE != SZ_4K)
>> +        /* Only 4k page size on the host is supported */
>> +        return 0;
>> +
>> +    if (rmi_check_version())
>> +        /* Continue without realm support */
>> +        return 0;
>> +
>> +    /* Future patch will enable static branch kvm_rme_is_available */
>> +
>> +    return 0;
>
> Do we ever expect this to fail the kvm initialisation ? Otherwise, we
> could leave it as a void ?

Technically in a later patch the return from rme_vmid_init() can cause
such a failure. But it's not clear that it makes any sense to completely
kill KVM because of that. So I'll change this to a void return.

Thanks,

Steve