linux-kernel - Re: [PATCH V4 0/3] KVM/Hyper-V: Add Hyper-V direct tlb flush support

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Message-ID: <874l1baqnf.fsf@vitty.brq.redhat.com>
Date:   Tue, 17 Sep 2019 17:28:20 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Tianyu Lan <Tianyu.Lan@...rosoft.com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, lantianyu1986@...il.com,
        rkrcmar@...hat.com, corbet@....net, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com, sashal@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, michael.h.kelley@...rosoft.com
Subject: Re: [PATCH V4 0/3] KVM/Hyper-V: Add Hyper-V direct tlb flush support

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 22/08/19 16:30, lantianyu1986@...il.com wrote:
>> From: Tianyu Lan <Tianyu.Lan@...rosoft.com>
>> 
>> This patchset is to add Hyper-V direct tlb support in KVM. Hyper-V
>> in L0 can delegate L1 hypervisor to handle tlb flush request from
>> L2 guest when direct tlb flush is enabled in L1.
>> 
>> Patch 2 introduces new cap KVM_CAP_HYPERV_DIRECT_TLBFLUSH to enable
>> feature from user space. User space should enable this feature only
>> when Hyper-V hypervisor capability is exposed to guest and KVM profile
>> is hided. There is a parameter conflict between KVM and Hyper-V hypercall.
>> We hope L2 guest doesn't use KVM hypercall when the feature is
>> enabled. Detail please see comment of new API "KVM_CAP_HYPERV_DIRECT_TLBFLUSH"
>> 
>> Change since v3:
>>        - Update changelog in each patches. 
>> 
>> Change since v2:
>>        - Move hv assist page(hv_pa_pg) from struct kvm  to struct kvm_hv.
>> 
>> Change since v1:
>>        - Fix offset issue in the patch 1.
>>        - Update description of KVM KVM_CAP_HYPERV_DIRECT_TLBFLUSH.
>> 
>> Tianyu Lan (2):
>>   x86/Hyper-V: Fix definition of struct hv_vp_assist_page
>>   KVM/Hyper-V: Add new KVM capability KVM_CAP_HYPERV_DIRECT_TLBFLUSH
>> 
>> Vitaly Kuznetsov (1):
>>   KVM/Hyper-V/VMX: Add direct tlb flush support
>> 
>>  Documentation/virtual/kvm/api.txt  | 13 +++++++++++++
>>  arch/x86/include/asm/hyperv-tlfs.h | 24 ++++++++++++++++++-----
>>  arch/x86/include/asm/kvm_host.h    |  4 ++++
>>  arch/x86/kvm/vmx/evmcs.h           |  2 ++
>>  arch/x86/kvm/vmx/vmx.c             | 39 ++++++++++++++++++++++++++++++++++++++
>>  arch/x86/kvm/x86.c                 |  8 ++++++++
>>  include/uapi/linux/kvm.h           |  1 +
>>  7 files changed, 86 insertions(+), 5 deletions(-)
>> 
>
> Queued, thanks.
>

I had a suggestion how we can get away without the new capability (like
direct tlb flush gets automatically enabled when Hyper-V hypercall page
is activated and we know we can't handle KVM hypercalls any more)
but this can probably be done as a follow-up.

-- 
Vitaly