Re: [PATCH] x86/sev: Do not fail SNP platform init if the vTPM cannot be registered

[Stefano Garzarella <sgarzare@redhat.com>]

On Fri, Aug 21, 2026 at 11:04:11AM +0530, Gokul K wrote:
>The SVSM vTPM is optional: snp_svsm_vtpm_probe() returns false when no
>SVSM is present or when it does not implement TPM_SEND_COMMAND, and
>snp_init_platform_device() happily returns success in that case.
>
>When the vTPM *is* available but registering its platform device fails,
>the same function instead returns -ENODEV, after sev_guest_device has
>already been registered.  That is worse than the absent-vTPM case in two
>ways: the sev-guest device is left registered while the initcall reports
>failure, and the error tells nobody anything, because the return value of
>a device_initcall is only ever traced, never acted upon.
>
>Log the failure and carry on, so an optional device that could not be
>registered no longer determines the fate of an unrelated one.  The vTPM
>is simply absent, which is a state the guest already has to cope with.
>
>Fixes: e396dd85172c ("x86/sev: Register tpm-svsm platform device")
>Signed-off-by: Gokul K <gokul02k@gmail.com>
>---
>Compile-tested only.  Reaching the failure path needs an SNP guest under an
>SVSM whose vTPM platform device fails to register, which in practice means
>-ENOMEM during initcalls; I have no way to reproduce that.  Built at W=1 with
>CONFIG_AMD_MEM_ENCRYPT=y, and confirmed the file is not built with it =n.
>
> arch/x86/coco/sev/core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
>index ecd77d3217f3..6501b6f7469a 100644
>--- a/arch/x86/coco/sev/core.c
>+++ b/arch/x86/coco/sev/core.c
>@@ -1401,7 +1401,7 @@ static int __init snp_init_platform_device(void)
>
> 	if (snp_svsm_vtpm_probe() &&
> 	    platform_device_register(&tpm_svsm_device))
>-		return -ENODEV;
>+		pr_err("Failed to register the SVSM vTPM device\n");

IIUC platform_device_register() fails only if something is really bad, 
no memory, device already registered, etc. so IMO this should never 
happen.

I'm opposed convert to an error message, but honestly I don't understand 
which problem we are fixing.

Stefano

>
> 	pr_info("SNP guest platform devices initialized.\n");
> 	return 0;
>-- 
>2.54.0
>
>