linux-kernel - Re: [PATCH v3 23/25] KVM: TDX: Use guard() to acquire kvm->lock in tdx_vm

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Message-ID: <aPe7M1aUPwqDmQbY@google.com>
Date: Tue, 21 Oct 2025 09:56:19 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Rick P Edgecombe <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH v3 23/25] KVM: TDX: Use guard() to acquire kvm->lock in tdx_vm_ioctl()

On Tue, Oct 21, 2025, Rick P Edgecombe wrote:
> On Thu, 2025-10-16 at 17:32 -0700, Sean Christopherson wrote:
> > Use guard() in tdx_vm_ioctl() to tidy up the code a small amount, but more
> > importantly to minimize the diff of a future change, which will use
> > guard-like semantics to acquire and release multiple locks.
> > 
> > No functional change intended.
> 
> There is a tiny functional change. In the default case it no longer re-copies
> the struct back to userspace.

No?  The default case doesn't copy the struct back even before this patch, it
explicitly skips the copy_to_user().

	mutex_lock(&kvm->lock);

	switch (tdx_cmd.id) {
	case KVM_TDX_CAPABILITIES:
		r = tdx_get_capabilities(&tdx_cmd);
		break;
	case KVM_TDX_INIT_VM:
		r = tdx_td_init(kvm, &tdx_cmd);
		break;
	case KVM_TDX_FINALIZE_VM:
		r = tdx_td_finalize(kvm, &tdx_cmd);
		break;
	default:
		r = -EINVAL;
		goto out;  <====================
	}

	if (copy_to_user(argp, &tdx_cmd, sizeof(struct kvm_tdx_cmd)))
		r = -EFAULT;

out:
	mutex_unlock(&kvm->lock);
	return r;