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SubjectRe: [PATCH 01/12] KVM: x86: Add a framework for enabling KVM-governed x86 features
Date
Sean Christopherson <seanjc@google.com> writes:

> Introduce yet another X86_FEATURE flag framework to manage and cache KVM
> governed features (for lack of a better term). "Governed" in this case
> means that KVM has some level of involvement and/or vested interest in
> whether or not an X86_FEATURE can be used by the guest. The intent of the
> framework is twofold: to simplify caching of guest CPUID flags that KVM
> needs to frequently query, and to add clarity to such caching, e.g. it
> isn't immediately obvious that SVM's bundle of flags for "optional nested]

Nit: unneeded ']'

> SVM features" track whether or not a flag is exposed to L1.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/include/asm/kvm_host.h | 11 +++++++
> arch/x86/kvm/cpuid.c | 2 ++
> arch/x86/kvm/cpuid.h | 51 ++++++++++++++++++++++++++++++++
> arch/x86/kvm/governed_features.h | 9 ++++++
> 4 files changed, 73 insertions(+)
> create mode 100644 arch/x86/kvm/governed_features.h
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 792a6037047a..cd660de02f7b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -835,6 +835,17 @@ struct kvm_vcpu_arch {
> struct kvm_cpuid_entry2 *cpuid_entries;
> struct kvm_hypervisor_cpuid kvm_cpuid;
>
> + /*
> + * Track whether or not the guest is allowed to use features that are
> + * governed by KVM, where "governed" means KVM needs to manage state
> + * and/or explicitly enable the feature in hardware. Typically, but
> + * not always, governed features can be used by the guest if and only
> + * if both KVM and userspace want to expose the feature to the guest.
> + */
> + struct {
> + u32 enabled;
> + } governed_features;
> +
> u64 reserved_gpa_bits;
> int maxphyaddr;
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8f8edeaf8177..013fdc27fc8f 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -335,6 +335,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> struct kvm_lapic *apic = vcpu->arch.apic;
> struct kvm_cpuid_entry2 *best;
>
> + vcpu->arch.governed_features.enabled = 0;
> +
> best = kvm_find_cpuid_entry(vcpu, 1);
> if (best && apic) {
> if (cpuid_entry_has(best, X86_FEATURE_TSC_DEADLINE_TIMER))
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index b1658c0de847..f61a2106ba90 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -232,4 +232,55 @@ static __always_inline bool guest_pv_has(struct kvm_vcpu *vcpu,
> return vcpu->arch.pv_cpuid.features & (1u << kvm_feature);
> }
>
> +enum kvm_governed_features {
> +#define KVM_GOVERNED_FEATURE(x) KVM_GOVERNED_##x,
> +#include "governed_features.h"
> + KVM_NR_GOVERNED_FEATURES
> +};
> +
> +static __always_inline int kvm_governed_feature_index(unsigned int x86_feature)
> +{
> + switch (x86_feature) {
> +#define KVM_GOVERNED_FEATURE(x) case x: return KVM_GOVERNED_##x;
> +#include "governed_features.h"
> + default:
> + return -1;
> + }
> +}
> +
> +static __always_inline int kvm_is_governed_feature(unsigned int x86_feature)
> +{
> + return kvm_governed_feature_index(x86_feature) >= 0;
> +}
> +
> +static __always_inline u32 kvm_governed_feature_bit(unsigned int x86_feature)
> +{
> + int index = kvm_governed_feature_index(x86_feature);
> +
> + BUILD_BUG_ON(index < 0);
> + return BIT(index);
> +}
> +
> +static __always_inline void kvm_governed_feature_set(struct kvm_vcpu *vcpu,
> + unsigned int x86_feature)
> +{
> + BUILD_BUG_ON(KVM_NR_GOVERNED_FEATURES >
> + sizeof(vcpu->arch.governed_features.enabled) * BITS_PER_BYTE);
> +
> + vcpu->arch.governed_features.enabled |= kvm_governed_feature_bit(x86_feature);
> +}
> +
> +static __always_inline void kvm_governed_feature_check_and_set(struct kvm_vcpu *vcpu,
> + unsigned int x86_feature)
> +{
> + if (guest_cpuid_has(vcpu, x86_feature))
> + kvm_governed_feature_set(vcpu, x86_feature);
> +}
> +
> +static __always_inline bool guest_can_use(struct kvm_vcpu *vcpu,
> + unsigned int x86_feature)
> +{
> + return vcpu->arch.governed_features.enabled & kvm_governed_feature_bit(x86_feature);
> +}
> +
> #endif
> diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
> new file mode 100644
> index 000000000000..40ce8e6608cd
> --- /dev/null
> +++ b/arch/x86/kvm/governed_features.h
> @@ -0,0 +1,9 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#if !defined(KVM_GOVERNED_FEATURE) || defined(KVM_GOVERNED_X86_FEATURE)
> +BUILD_BUG()
> +#endif
> +
> +#define KVM_GOVERNED_X86_FEATURE(x) KVM_GOVERNED_FEATURE(X86_FEATURE_##x)
> +
> +#undef KVM_GOVERNED_X86_FEATURE
> +#undef KVM_GOVERNED_FEATURE

--
Vitaly

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