linux-kernel - Re: [PATCH] KVM: TDX: Allow userspace to return errors to guest for MAPGPA

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Message-ID: <43a0558a-4cca-4d9c-97dc-ffd085186fd9@intel.com>
Date: Wed, 14 Jan 2026 10:59:00 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sagi Shahar <sagis@...gle.com>, Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Kiryl Shutsemau <kas@...nel.org>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: Thomas Gleixner <tglx@...nel.org>, Borislav Petkov <bp@...en8.de>,
 "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev,
 Vishal Annapurve <vannapurve@...gle.com>
Subject: Re: [PATCH] KVM: TDX: Allow userspace to return errors to guest for
 MAPGPA

On 1/14/2026 8:30 AM, Sagi Shahar wrote:
> From: Vishal Annapurve <vannapurve@...gle.com>
> 
> MAPGPA request from TDX VMs gets split into chunks by KVM using a loop
> of userspace exits until the complete range is handled.
> 
> In some cases userspace VMM might decide to break the MAPGPA operation
> and continue it later. For example: in the case of intrahost migration
> userspace might decide to continue the MAPGPA operation after the
> migrration is completed.
> 
> Allow userspace to signal to TDX guests that the MAPGPA operation should
> be retried the next time the guest is scheduled.
> 
> Signed-off-by: Vishal Annapurve <vannapurve@...gle.com>
> Co-developed-by: Sagi Shahar <sagis@...gle.com>
> Signed-off-by: Sagi Shahar <sagis@...gle.com>
> ---
>   arch/x86/kvm/vmx/tdx.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 2d7a4d52ccfb..3244064b1a04 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1189,7 +1189,13 @@ static int tdx_complete_vmcall_map_gpa(struct kvm_vcpu *vcpu)
>   	struct vcpu_tdx *tdx = to_tdx(vcpu);
>   
>   	if (vcpu->run->hypercall.ret) {
> -		tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);
> +		if (vcpu->run->hypercall.ret == -EBUSY)
> +			tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_RETRY);
> +		else if (vcpu->run->hypercall.ret == -EINVAL)
> +			tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);
> +		else
> +			return -EINVAL;

It's incorrect to return -EINVAL here. The -EINVAL will eventually be 
returned to userspace for the VCPU_RUN ioctl. It certainly breaks 
userspace. So it needs to be

	if (vcpu->run->hypercall.ret == -EBUSY)
		tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_RETRY);
	else
		tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);

But I'm not sure if such change breaks the userspace ABI that if needs 
to be opted-in.