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

From: Paolo Bonzini <pbonzini@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>, kvm@vger.kernel.org
Cc: Sean Christopherson <seanjc@google.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>
Subject: Re: [PATCH v2 00/15] KVM: x86: Conditional Hyper-V emulation enablement
Date: Thu, 28 Jan 2021 15:25:25 +0100	[thread overview]
Message-ID: <b88c62a9-2c64-4de9-b27e-dce969bf8c07@redhat.com> (raw)
In-Reply-To: <20210126134816.1880136-1-vkuznets@redhat.com>

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
> 
>   arch/x86/include/asm/kvm_host.h               |   4 +-
>   arch/x86/kvm/cpuid.c                          |   2 +
>   arch/x86/kvm/hyperv.c                         | 301 +++++++++++-------
>   arch/x86/kvm/hyperv.h                         |  54 ++--
>   arch/x86/kvm/lapic.c                          |   5 +-
>   arch/x86/kvm/lapic.h                          |   7 +-
>   arch/x86/kvm/vmx/vmx.c                        |   9 +-
>   arch/x86/kvm/x86.c                            |  19 +-
>   .../selftests/kvm/include/x86_64/processor.h  |   3 +
>   .../selftests/kvm/lib/x86_64/processor.c      |  33 ++
>   .../testing/selftests/kvm/x86_64/evmcs_test.c |  39 ++-
>   .../selftests/kvm/x86_64/hyperv_cpuid.c       |  31 +-
>   12 files changed, 314 insertions(+), 193 deletions(-)
> 

Queued, thanks.

Paolo