linux-kernel - Re: [PATCH v2 03/12] x86/sev: Add an x86 version of prot_guest

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Message-ID: <YRgUxyhoqVJ0Kxvt@zn.tnic>
Date:   Sat, 14 Aug 2021 21:08:55 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-graphics-maintainer@...are.com,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        Brijesh Singh <brijesh.singh@....com>,
        Joerg Roedel <joro@...tes.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH v2 03/12] x86/sev: Add an x86 version of prot_guest_has()

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@....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.

https://people.kernel.org/tglx/notes-about-netiquette