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

Borislav Petkov
2021-08-14T19:08:26Z

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.

- 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.

---
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;

--
Regards/Gruss,
Boris.