linux-kernel - Re: [PATCH v10 14/39] KVM: nSVM: Keep track of Hyper-V hv_vm_id/hv_vp

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Date:   Thu, 22 Sep 2022 11:51:10 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 14/39] KVM: nSVM: Keep track of Hyper-V
 hv_vm_id/hv_vp_id

Sean Christopherson <seanjc@...gle.com> writes:

> On Wed, Sep 21, 2022, Vitaly Kuznetsov wrote:
>> Similar to nSVM, KVM needs to know L2's VM_ID/VP_ID and Partition
>> assist page address to handle L2 TLB flush requests.
>> 
>> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>>  arch/x86/kvm/svm/hyperv.h | 16 ++++++++++++++++
>>  arch/x86/kvm/svm/nested.c |  2 ++
>>  2 files changed, 18 insertions(+)
>> 
>> diff --git a/arch/x86/kvm/svm/hyperv.h b/arch/x86/kvm/svm/hyperv.h
>> index 7d6d97968fb9..8cf702fed7e5 100644
>> --- a/arch/x86/kvm/svm/hyperv.h
>> +++ b/arch/x86/kvm/svm/hyperv.h
>> @@ -9,6 +9,7 @@
>>  #include <asm/mshyperv.h>
>>  
>>  #include "../hyperv.h"
>> +#include "svm.h"
>>  
>>  /*
>>   * Hyper-V uses the software reserved 32 bytes in VMCB
>> @@ -32,4 +33,19 @@ struct hv_enlightenments {
>>   */
>>  #define VMCB_HV_NESTED_ENLIGHTENMENTS VMCB_SW
>>  
>> +static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu)
>> +{
>> +	struct vcpu_svm *svm = to_svm(vcpu);
>> +	struct hv_enlightenments *hve =
>> +		(struct hv_enlightenments *)svm->nested.ctl.reserved_sw;
>
> Eww :-)
>
> I posted a small series to fix the casting[*], and as noted in the cover letter it's
> going to conflict mightily.  Ignoring merge order for the moment, looking at the
> series as a whole, if the Hyper-V definitions are moved to hyperv-tlfs.h, then I'm
> tempted to say there's no need for svm/hyperv.h.
>
> There should never be users of this stuff outside of svm/nested.c, and IMO there's
> not enough stuff to warrant a separate set of files.  nested_svm_hv_update_vp_assist()
> isn't SVM specific and fits better alongside kvm_hv_get_assist_page().
>
> That leaves three functions and ~40 lines of code, which can easily go directly
> into svm/nested.c.
>
> I'm definitely not dead set against having hyperv.{ch}, but unless there's a high
> probability of SVM+Hyper-V getting to eVMCS levels of enlightenment, my vote is
> to put these helpers in svm/nested.c and move then if/when we do end up accumulating
> more SVM+Hyper-V code.

Well, there's more on the TODO list :-) There are even nSVM-only
features like "enlightened TLB" (to split ASID invalidations into two
stages) so I don't want to pollute 'nested.c'. In fact, I was thinking
about renaming vmx/evmcs.{ch} into vmx/hyperv.{ch} as we're doing more
than eVMCS there already. Also, having separate files help with the
newly introduces 'KVM X86 HYPER-V (KVM/hyper-v)' MAINTAINERS entry. Does
this sound like a good enough justification for keeping hyperv.{ch}?

>   
> As for merge order, I don't think there's a need for this series to take a
> dependency on the cleanup, especially if these helpers land in nested.c.  Fixing
> up the casting and s/hv_enlightenments/hv_vmcb_enlightenments is straightforward.
>
> [*] https://lore.kernel.org/all/20220921201607.3156750-1-seanjc@google.com
>

I'll take a look, thanks!

-- 
Vitaly