Re: [RFC 04/33] KVM: x86: hyper-v: Move hypercall page handling into separate function

[Maxim Levitsky]

On Wed, 2023-11-08 at 11:17 +0000, Nicolas Saenz Julienne wrote:
> The hypercall page patching is about to grow considerably, move it into
> its own function.
> 
> No functional change intended.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>
> ---
>  arch/x86/kvm/hyperv.c | 69 ++++++++++++++++++++++++-------------------
>  1 file changed, 39 insertions(+), 30 deletions(-)
> 
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index e1bc861ab3b0..78d053042667 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -256,6 +256,42 @@ static void synic_exit(struct kvm_vcpu_hv_synic *synic, u32 msr)
>  	kvm_make_request(KVM_REQ_HV_EXIT, vcpu);
>  }
>  
> +static int patch_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +	u8 instructions[9];
> +	int i = 0;
> +	u64 addr;
> +
> +	/*
> +	 * If Xen and Hyper-V hypercalls are both enabled, disambiguate
> +	 * the same way Xen itself does, by setting the bit 31 of EAX
> +	 * which is RsvdZ in the 32-bit Hyper-V hypercall ABI and just
> +	 * going to be clobbered on 64-bit.
> +	 */
> +	if (kvm_xen_hypercall_enabled(kvm)) {
> +		/* orl $0x80000000, %eax */
> +		instructions[i++] = 0x0d;
> +		instructions[i++] = 0x00;
> +		instructions[i++] = 0x00;
> +		instructions[i++] = 0x00;
> +		instructions[i++] = 0x80;
> +	}
> +
> +	/* vmcall/vmmcall */
> +	static_call(kvm_x86_patch_hypercall)(vcpu, instructions + i);
> +	i += 3;
> +
> +	/* ret */
> +	((unsigned char *)instructions)[i++] = 0xc3;
> +
> +	addr = data & HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_MASK;
> +	if (kvm_vcpu_write_guest(vcpu, addr, instructions, i))
> +		return 1;
> +
> +	return 0;
> +}
> +
>  static int synic_set_msr(struct kvm_vcpu_hv_synic *synic,
>  			 u32 msr, u64 data, bool host)
>  {
> @@ -1338,11 +1374,7 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
>  		if (!hv->hv_guest_os_id)
>  			hv->hv_hypercall &= ~HV_X64_MSR_HYPERCALL_ENABLE;
>  		break;
> -	case HV_X64_MSR_HYPERCALL: {
> -		u8 instructions[9];
> -		int i = 0;
> -		u64 addr;
> -
> +	case HV_X64_MSR_HYPERCALL:
>  		/* if guest os id is not set hypercall should remain disabled */
>  		if (!hv->hv_guest_os_id)
>  			break;
> @@ -1351,34 +1383,11 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
>  			break;
>  		}
>  
> -		/*
> -		 * If Xen and Hyper-V hypercalls are both enabled, disambiguate
> -		 * the same way Xen itself does, by setting the bit 31 of EAX
> -		 * which is RsvdZ in the 32-bit Hyper-V hypercall ABI and just
> -		 * going to be clobbered on 64-bit.
> -		 */
> -		if (kvm_xen_hypercall_enabled(kvm)) {
> -			/* orl $0x80000000, %eax */
> -			instructions[i++] = 0x0d;
> -			instructions[i++] = 0x00;
> -			instructions[i++] = 0x00;
> -			instructions[i++] = 0x00;
> -			instructions[i++] = 0x80;
> -		}
> -
> -		/* vmcall/vmmcall */
> -		static_call(kvm_x86_patch_hypercall)(vcpu, instructions + i);
> -		i += 3;
> -
> -		/* ret */
> -		((unsigned char *)instructions)[i++] = 0xc3;
> -
> -		addr = data & HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_MASK;
> -		if (kvm_vcpu_write_guest(vcpu, addr, instructions, i))
> +		if (patch_hypercall_page(vcpu, data))
>  			return 1;
> +
>  		hv->hv_hypercall = data;
>  		break;
> -	}
>  	case HV_X64_MSR_REFERENCE_TSC:
>  		hv->hv_tsc_page = data;
>  		if (hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE) {


This looks like another nice cleanup that can be accepted to the kvm,
before the main VTL patch series.

Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky