linux-kernel - Re: [RFC 12/33] KVM: x86: hyper-v: Handle VSM hcalls in user-space

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Date:   Tue, 28 Nov 2023 09:28:37 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     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, graf@...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 12/33] KVM: x86: hyper-v: Handle VSM hcalls in user-space

On Wed, 2023-11-08 at 11:17 +0000, Nicolas Saenz Julienne wrote:
> Let user-space handle all hypercalls that fall under the AccessVsm
> partition privilege flag. That is:
>  - HVCALL_MODIFY_VTL_PROTECTION_MASK:
>  - HVCALL_ENABLE_PARTITION_VTL:
>  - HVCALL_ENABLE_VP_VTL:
>  - HVCALL_VTL_CALL:
>  - HVCALL_VTL_RETURN:
> The hypercalls are processed through the KVM_EXIT_HYPERV_HVCALL exit.
> Additionally, expose the cpuid bit.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
> ---
>  arch/x86/kvm/hyperv.c             | 15 +++++++++++++++
>  include/asm-generic/hyperv-tlfs.h |  7 ++++++-
>  2 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index a3970d52eef1..a266c5d393f5 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -2462,6 +2462,11 @@ static bool kvm_hv_is_xmm_output_hcall(u16 code)
>  	return false;
>  }
>  
> +static inline bool kvm_hv_is_vtl_call_return(u16 code)
> +{
> +	return code == HVCALL_VTL_CALL || code == HVCALL_VTL_RETURN;
> +}
> +
>  static int kvm_hv_hypercall_complete_userspace(struct kvm_vcpu *vcpu)
>  {
>  	bool fast = !!(vcpu->run->hyperv.u.hcall.input & HV_HYPERCALL_FAST_BIT);
> @@ -2471,6 +2476,9 @@ static int kvm_hv_hypercall_complete_userspace(struct kvm_vcpu *vcpu)
>  	if (kvm_hv_is_xmm_output_hcall(code) && hv_result_success(result) && fast)
>  		kvm_hv_write_xmm(vcpu->run->hyperv.u.hcall.xmm);
>  
> +	if (kvm_hv_is_vtl_call_return(code))
> +		return kvm_skip_emulated_instruction(vcpu);

Can you add justification for this?
If this is justified, does it make sense to move this code to kvm_hv_hypercall_complete
(which also calls kvm_skip_emulated_instruction())



> +
>  	return kvm_hv_hypercall_complete(vcpu, result);
>  }
>  
> @@ -2525,6 +2533,7 @@ static bool is_xmm_fast_hypercall(struct kvm_hv_hcall *hc)
>  	case HVCALL_SEND_IPI_EX:
>  	case HVCALL_GET_VP_REGISTERS:
>  	case HVCALL_SET_VP_REGISTERS:
> +	case HVCALL_MODIFY_VTL_PROTECTION_MASK:
>  		return true;
>  	}
>  
> @@ -2745,6 +2754,11 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
>  		goto hypercall_userspace_exit;
>  	case HVCALL_GET_VP_REGISTERS:
>  	case HVCALL_SET_VP_REGISTERS:
> +	case HVCALL_MODIFY_VTL_PROTECTION_MASK:
> +	case HVCALL_ENABLE_PARTITION_VTL:
> +	case HVCALL_ENABLE_VP_VTL:
> +	case HVCALL_VTL_CALL:
> +	case HVCALL_VTL_RETURN:
>  		goto hypercall_userspace_exit;
>  	default:

Also those new hypercalls also should be added to hv_check_hypercall_access.

>  		ret = HV_STATUS_INVALID_HYPERCALL_CODE;
> @@ -2912,6 +2926,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>  			ent->ebx |= HV_SIGNAL_EVENTS;
>  			ent->ebx |= HV_ENABLE_EXTENDED_HYPERCALLS;
>  			ent->ebx |= HV_ACCESS_VP_REGISTERS;
> +			ent->ebx |= HV_ACCESS_VSM;
>  
>  			ent->edx |= HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE;
>  			ent->edx |= HV_X64_HYPERCALL_XMM_OUTPUT_AVAILABLE;

Best regards,
	Maxim Levitsky

> diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> index 24ea699a3d8e..a8b5c8a84bbc 100644
> --- a/include/asm-generic/hyperv-tlfs.h
> +++ b/include/asm-generic/hyperv-tlfs.h
> @@ -89,6 +89,7 @@
>  #define HV_ACCESS_STATS				BIT(8)
>  #define HV_DEBUGGING				BIT(11)
>  #define HV_CPU_MANAGEMENT			BIT(12)
> +#define HV_ACCESS_VSM				BIT(16)
>  #define HV_ACCESS_VP_REGISTERS			BIT(17)
>  #define HV_ENABLE_EXTENDED_HYPERCALLS		BIT(20)
>  #define HV_ISOLATION				BIT(22)
> @@ -147,9 +148,13 @@ union hv_reference_tsc_msr {
>  /* Declare the various hypercall operations. */
>  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE	0x0002
>  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST	0x0003
> -#define HVCALL_ENABLE_VP_VTL			0x000f
>  #define HVCALL_NOTIFY_LONG_SPIN_WAIT		0x0008
>  #define HVCALL_SEND_IPI				0x000b
> +#define HVCALL_MODIFY_VTL_PROTECTION_MASK	0x000c
> +#define HVCALL_ENABLE_PARTITION_VTL		0x000d
> +#define HVCALL_ENABLE_VP_VTL			0x000f
> +#define HVCALL_VTL_CALL				0x0011
> +#define HVCALL_VTL_RETURN			0x0012
>  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX	0x0013
>  #define HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX	0x0014
>  #define HVCALL_SEND_IPI_EX			0x0015