Re: [PATCH 1/3] x86/coco: Add CC_ATTR_GUEST_SEV

[Tom Lendacky]

On 9/9/26 22:35, Borislav Petkov wrote:
> On Wed, Sep 09, 2026 at 07:40:27PM -0700, Borislav Petkov wrote:
>> On Mon, Aug 03, 2026 at 02:58:25PM +0200, Jörg Rödel wrote:
>>> From: Joerg Roedel <joerg.roedel@xxxxxxx>
>>>
>>> Add a new attribute to the CC platform code to check whether the
>>> kernel runs in an environment using SEV memory encryption. This will
>>> be used to establish the an sev/ directory in SYSFS (which is
>>> currently SEV-SNP-only).
>>
>> Yeah, the initial intention for cc_plaform_has() is to use it in arch-agnostic
>> code and for something which you're going to use in coco code itself, you're
>> better off simply doing:
>>
>> 	if (sev_status & MSR_AMD64_SEV_ENABLED)
>>
>> I can fix that up when applying if you prefer - it is easy enough.
> 
> IOW, I merged them all three into this simple one.
> 
> Author: Joerg Roedel <joerg.roedel@xxxxxxx>
> Date:   Mon Aug 3 14:58:25 2026 +0200
> 
>     x86/sev: Report MSR_AMD64_SEV in sysfs
>     
>     Add SEV_STATUS to the cpu/sev/ sysfs hierarchy and report it for all SEV
>     guest types.
>     
>       [ bp: Merge into a single patch, simplify. ]
>     
>     Signed-off-by: Joerg Roedel <joerg.roedel@xxxxxxx>
>     Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
>     Link: https://patch.msgid.link/20260803125827.718024-2-joro@xxxxxxxxxx

Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

Minor nit below, up to you.

> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index 82d10d556cc8..cec413a71491 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -690,15 +690,20 @@ Description:	Umwait control
>  
>  What:		/sys/devices/system/cpu/sev
>  		/sys/devices/system/cpu/sev/vmpl
> +		/sys/devices/system/cpu/sev/sev_status

See below...

>  Date:		May 2024
>  Contact:	Linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>
>  Description:	Secure Encrypted Virtualization (SEV) information
>  
> -		This directory is only present when running as an SEV-SNP guest.
> +		This directory is only present when running as an SEV guest.
>  
>  		vmpl: Reports the Virtual Machine Privilege Level (VMPL) at which
> -		      the SEV-SNP guest is running.
> +		      the SEV-SNP guest is running. This file is only present
> +		      when running as an SEV-SNP guest.
>  
> +		sev_status: Reports the value of the SEV_STATUS MSR which
> +			    enumerates the enabled features of an SEV
> +			    environment.

Maybe try to keep in alphabetical order and move above the vmpl entry?

Thanks,
Tom

>  
>  What:		/sys/devices/system/cpu/svm
>  Date:		August 2019
> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> index ec8fc02bd636..4751bfbe694f 100644
> --- a/arch/x86/coco/sev/core.c
> +++ b/arch/x86/coco/sev/core.c
> @@ -1431,15 +1431,22 @@ static ssize_t vmpl_show(struct kobject *kobj,
>  	return sysfs_emit(buf, "%d\n", snp_vmpl);
>  }
>  
> +static ssize_t sev_status_show(struct kobject *kobj,
> +			       struct kobj_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "0x%llx\n", sev_status);
> +}
> +
>  static struct kobj_attribute vmpl_attr = __ATTR_RO(vmpl);
> +static struct kobj_attribute sev_status_attr = __ATTR_RO(sev_status);
>  
> -static struct attribute *vmpl_attrs[] = {
> -	&vmpl_attr.attr,
> +static struct attribute *sev_status_attrs[] = {
> +	&sev_status_attr.attr,
>  	NULL
>  };
>  
>  static struct attribute_group sev_attr_group = {
> -	.attrs = vmpl_attrs,
> +	.attrs = sev_status_attrs,
>  };
>  
>  static int __init sev_sysfs_init(void)
> @@ -1448,7 +1455,7 @@ static int __init sev_sysfs_init(void)
>  	struct device *dev_root;
>  	int ret;
>  
> -	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> +	if (!(sev_status & MSR_AMD64_SEV_ENABLED))
>  		return -ENODEV;
>  
>  	dev_root = bus_get_dev_root(&cpu_subsys);
> @@ -1463,7 +1470,20 @@ static int __init sev_sysfs_init(void)
>  
>  	ret = sysfs_create_group(sev_kobj, &sev_attr_group);
>  	if (ret)
> -		kobject_put(sev_kobj);
> +		goto drop_kobj;
> +
> +	if (sev_status & MSR_AMD64_SEV_SNP_ENABLED) {
> +		ret = sysfs_add_file_to_group(sev_kobj, &vmpl_attr.attr, NULL);
> +		if (ret)
> +			goto drop_sysfs;
> +	}
> +
> +	return 0;
> +
> +drop_sysfs:
> +	sysfs_remove_group(sev_kobj, &sev_attr_group);
> +drop_kobj:
> +	kobject_put(sev_kobj);
>  
>  	return ret;
>  }
> 
>>
>> -- 
>> Regards/Gruss,
>>     Boris.
>>
>> https://people.kernel.org/tglx/notes-about-netiquette
>