linux-kernel - Re: [RFC 11/33] KVM: x86: hyper-v: Handle GET/SET_VP

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Message-ID: <38e52b16dfb57d0759b0e196fc952f20a62b0d3f.camel@redhat.com>
Date:   Tue, 28 Nov 2023 09:26:48 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Alexander Graf <graf@...zon.com>,
        Nicolas Saenz Julienne <nsaenz@...zon.com>,
        kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        anelkz@...zon.com, dwmw@...zon.co.uk, jgowans@...zon.com,
        corbert@....net, kys@...rosoft.com, haiyangz@...rosoft.com,
        decui@...rosoft.com, x86@...nel.org, linux-doc@...r.kernel.org
Subject: Re: [RFC 11/33] KVM: x86: hyper-v: Handle GET/SET_VP_REGISTER hcall
 in user-space

On Wed, 2023-11-08 at 13:14 +0100, Alexander Graf wrote:
> On 08.11.23 12:17, Nicolas Saenz Julienne wrote:
> > Let user-space handle HVCALL_GET_VP_REGISTERS and
> > HVCALL_SET_VP_REGISTERS through the KVM_EXIT_HYPERV_HVCALL exit reason.
> > Additionally, expose the cpuid bit.
> > 
> > Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
> > ---
> >   arch/x86/kvm/hyperv.c             | 9 +++++++++
> >   include/asm-generic/hyperv-tlfs.h | 1 +
> >   2 files changed, 10 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> > index caaa859932c5..a3970d52eef1 100644
> > --- a/arch/x86/kvm/hyperv.c
> > +++ b/arch/x86/kvm/hyperv.c
> > @@ -2456,6 +2456,9 @@ static void kvm_hv_write_xmm(struct kvm_hyperv_xmm_reg *xmm)
> >   
> >   static bool kvm_hv_is_xmm_output_hcall(u16 code)
> >   {
> > +	if (code == HVCALL_GET_VP_REGISTERS)
> > +		return true;
> > +
> >   	return false;
> >   }
> >   
> > @@ -2520,6 +2523,8 @@ static bool is_xmm_fast_hypercall(struct kvm_hv_hcall *hc)
> >   	case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX:
> >   	case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX:
> >   	case HVCALL_SEND_IPI_EX:
> > +	case HVCALL_GET_VP_REGISTERS:
> > +	case HVCALL_SET_VP_REGISTERS:
> >   		return true;
> >   	}
> >   
> > @@ -2738,6 +2743,9 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> >   			break;
> >   		}
> >   		goto hypercall_userspace_exit;
> > +	case HVCALL_GET_VP_REGISTERS:
> > +	case HVCALL_SET_VP_REGISTERS:
> > +		goto hypercall_userspace_exit;
> >   	default:
> >   		ret = HV_STATUS_INVALID_HYPERCALL_CODE;
> >   		break;
> > @@ -2903,6 +2911,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
> >   			ent->ebx |= HV_POST_MESSAGES;
> >   			ent->ebx |= HV_SIGNAL_EVENTS;
> >   			ent->ebx |= HV_ENABLE_EXTENDED_HYPERCALLS;
> > +			ent->ebx |= HV_ACCESS_VP_REGISTERS;
> 
> Do we need to guard this?

I think so, check should be added to 'hv_check_hypercall_access'.

I do wonder though why KVM can't just pass all unknown hypercalls to userspace
instead of having a whitelist.


Best regards,
	Maxim Levitsky

> 
> 
> Alex
> 
> 
> 
> 
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