linux-kernel - Re: [PATCH v3 13/34] KVM: nSVM: Keep track of Hyper-V hv_vm_id/hv_vp

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Date:   Wed, 11 May 2022 14:27:10 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 13/34] KVM: nSVM: Keep track of Hyper-V
 hv_vm_id/hv_vp_id

On Thu, 2022-04-14 at 15:19 +0200, 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.
> 
> 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;

Small nitpick:

Can we use this as an opportunity to rename the 'reserved_sw' to \
'hv_enlightenments' or something, because that is what it is?

Also the reserved_sw is an array, which is confusing, since from first look,
it looks like we have a pointer dereference here.



> +	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> +
> +	if (!hv_vcpu)
> +		return;
> +
> +	hv_vcpu->nested.pa_page_gpa = hve->partition_assist_page;
> +	hv_vcpu->nested.vm_id = hve->hv_vm_id;
> +	hv_vcpu->nested.vp_id = hve->hv_vp_id;
> +}
> +
>  #endif /* __ARCH_X86_KVM_SVM_HYPERV_H__ */
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index bed5e1692cef..2d1a76343404 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -826,6 +826,8 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
>  
>  	svm->nested.nested_run_pending = 1;
>  
> +	nested_svm_hv_update_vm_vp_ids(vcpu);
> +
>  	if (enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12, true))
>  		goto out_exit_err;
>  

That won't work after migration, since this won't be called
if we migrate with nested guest running.


I think that nested_svm_hv_update_vm_vp_ids should be called 
from enter_svm_guest_mode.


Best regards,
	Maxim Levitsky