Re: [PATCH v2 00/15] KVM: x86: Conditional Hyper-V emulation enablement

[Paolo Bonzini <pbonzini@redhat.com>]

On 08/02/21 15:18, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
> 
>> On 26/01/21 14:48, Vitaly Kuznetsov wrote:
>>> Changes since v1 [Sean]:
>>> - Add a few cleanup patches ("Rename vcpu_to_hv_vcpu() to to_hv_vcpu()",
>>>     "Rename vcpu_to_synic()/synic_to_vcpu()", ...)
>>> - Drop unused kvm_hv_vapic_assist_page_enabled()
>>> - Stop shadowing global 'current_vcpu' variable in kvm_hv_flush_tlb()/
>>>     kvm_hv_send_ipi()
>>>
>>> Original description:
>>>
>>> Hyper-V emulation is enabled in KVM unconditionally even for Linux guests.
>>> This is bad at least from security standpoint as it is an extra attack
>>> surface. Ideally, there should be a per-VM capability explicitly enabled by
>>> VMM but currently it is not the case and we can't mandate one without
>>> breaking backwards compatibility. We can, however, check guest visible CPUIDs
>>> and only enable Hyper-V emulation when "Hv#1" interface was exposed in
>>> HYPERV_CPUID_INTERFACE.
>>>
>>> Also (and while on it) per-vcpu Hyper-V context ('struct kvm_vcpu_hv') is
>>> currently part of 'struct kvm_vcpu_arch' and thus allocated unconditionally
>>> for each vCPU. The context, however, quite big and accounts for more than
>>> 1/4 of 'struct kvm_vcpu_arch' (e.g. 2912/9512 bytes). Switch to allocating
>>> it dynamically. This may come handy if we ever decide to raise KVM_MAX_VCPUS
>>> (and rumor has it some downstream distributions already have more than '288')
>>>
>>> Vitaly Kuznetsov (15):
>>>     selftests: kvm: Move kvm_get_supported_hv_cpuid() to common code
>>>     selftests: kvm: Properly set Hyper-V CPUIDs in evmcs_test
>>>     KVM: x86: hyper-v: Drop unused kvm_hv_vapic_assist_page_enabled()
>>>     KVM: x86: hyper-v: Rename vcpu_to_hv_vcpu() to to_hv_vcpu()
>>>     KVM: x86: hyper-v: Rename vcpu_to_synic()/synic_to_vcpu()
>>>     KVM: x86: hyper-v: Rename vcpu_to_stimer()/stimer_to_vcpu()
>>>     KVM: x86: hyper-v: Rename vcpu_to_hv_syndbg() to to_hv_syndbg()
>>>     KVM: x86: hyper-v: Introduce to_kvm_hv() helper
>>>     KVM: x86: hyper-v: Stop shadowing global 'current_vcpu' variable
>>>     KVM: x86: hyper-v: Always use to_hv_vcpu() accessor to get to 'struct
>>>       kvm_vcpu_hv'
>>>     KVM: x86: hyper-v: Prepare to meet unallocated Hyper-V context
>>>     KVM: x86: hyper-v: Allocate 'struct kvm_vcpu_hv' dynamically
>>>     KVM: x86: hyper-v: Make Hyper-V emulation enablement conditional
>>>     KVM: x86: hyper-v: Allocate Hyper-V context lazily
>>>     KVM: x86: hyper-v: Drop hv_vcpu_to_vcpu() helper
>>>
> ...
>>>
>>
>> Queued, thanks.
> 
> I was expecting it to appear in kvm/queue but it didn't happen so just
> wanted to double-check what happened to these patches. Thanks!

Added them back now (they conflicted with the Xen patches), thanks.

Paolo