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

From: Borislav Petkov <bp@alien8.de>
To: Tom Lendacky <thomas.lendacky@amd.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
	iommu@lists.linux-foundation.org, kvm@vger.kernel.org,
	linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
	linux-graphics-maintainer@vmware.com,
	amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org,
	Brijesh Singh <brijesh.singh@amd.com>,
	Joerg Roedel <joro@8bytes.org>, Andi Kleen <ak@linux.intel.com>,
	Sathyanarayanan Kuppuswamy 
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	Tianyu Lan <Tianyu.Lan@microsoft.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH v2 03/12] x86/sev: Add an x86 version of prot_guest_has()
Date: Sat, 14 Aug 2021 21:08:55 +0200	[thread overview]
Message-ID: <YRgUxyhoqVJ0Kxvt@zn.tnic> (raw)
In-Reply-To: <7d55bac0cf2e73f53816bce3a3097877ed9663f3.1628873970.git.thomas.lendacky@amd.com>

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.

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