Re: [PATCH v2 03/12] x86/sev: Add an x86 version of prot_guest_has()

[Tom Lendacky <thomas.lendacky@amd.com>]

On 8/14/21 2:08 PM, Borislav Petkov wrote:
> On Fri, Aug 13, 2021 at 11:59:22AM -0500, Tom Lendacky wrote:
>> diff --git a/arch/x86/include/asm/protected_guest.h b/arch/x86/include/asm/protected_guest.h
>> new file mode 100644
>> index 000000000000..51e4eefd9542
>> --- /dev/null
>> +++ b/arch/x86/include/asm/protected_guest.h
>> @@ -0,0 +1,29 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Protected Guest (and Host) Capability checks
>> + *
>> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
>> + *
>> + * Author: Tom Lendacky <thomas.lendacky@amd.com>
>> + */
>> +
>> +#ifndef _X86_PROTECTED_GUEST_H
>> +#define _X86_PROTECTED_GUEST_H
>> +
>> +#include <linux/mem_encrypt.h>
>> +
>> +#ifndef __ASSEMBLY__
>> +
>> +static inline bool prot_guest_has(unsigned int attr)
>> +{
>> +#ifdef CONFIG_AMD_MEM_ENCRYPT
>> +	if (sme_me_mask)
>> +		return amd_prot_guest_has(attr);
>> +#endif
>> +
>> +	return false;
>> +}
>> +
>> +#endif	/* __ASSEMBLY__ */
>> +
>> +#endif	/* _X86_PROTECTED_GUEST_H */
> 
> I think this can be simplified more, diff ontop below:
> 
> - no need for the ifdeffery as amd_prot_guest_has() has versions for
> both when CONFIG_AMD_MEM_ENCRYPT is set or not.

Ugh, yeah, not sure why I put that in for this version since I have the 
static inline for when CONFIG_AMD_MEM_ENCRYPT is not set.

> 
> - the sme_me_mask check is pushed there too.
> 
> - and since this is vendor-specific, I'm checking the vendor bit. Yeah,
> yeah, cross-vendor but I don't really believe that.

It's not a cross-vendor thing as opposed to a KVM or other hypervisor 
thing where the family doesn't have to be reported as AMD or HYGON. That's 
why I made the if check be for sme_me_mask. I think that is the safer way 
to go.

Thanks,
Tom

> 
> ---
> diff --git a/arch/x86/include/asm/protected_guest.h b/arch/x86/include/asm/protected_guest.h
> index 51e4eefd9542..8541c76d5da4 100644
> --- a/arch/x86/include/asm/protected_guest.h
> +++ b/arch/x86/include/asm/protected_guest.h
> @@ -12,18 +12,13 @@
>   
>   #include <linux/mem_encrypt.h>
>   
> -#ifndef __ASSEMBLY__
> -
>   static inline bool prot_guest_has(unsigned int attr)
>   {
> -#ifdef CONFIG_AMD_MEM_ENCRYPT
> -	if (sme_me_mask)
> +	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
> +	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
>   		return amd_prot_guest_has(attr);
> -#endif
>   
>   	return false;
>   }
>   
> -#endif	/* __ASSEMBLY__ */
> -
>   #endif	/* _X86_PROTECTED_GUEST_H */
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index edc67ddf065d..5a0442a6f072 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -392,6 +392,9 @@ bool noinstr sev_es_active(void)
>   
>   bool amd_prot_guest_has(unsigned int attr)
>   {
> +	if (!sme_me_mask)
> +		return false;
> +
>   	switch (attr) {
>   	case PATTR_MEM_ENCRYPT:
>   		return sme_me_mask != 0;
>