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

Sean Christopherson
2022-09-21T21:16:48Z

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@redhat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.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.

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