linux-kernel - [PATCH v5 11/16] x86/sme: Avoid SME/SVE related checks on non-SME/SVE platforms

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Date: Wed, 21 Feb 2024 12:35:18 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>, Kevin Loughlin <kevinloughlin@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>, Dionna Glaze <dionnaglaze@...gle.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, linux-arch@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: [PATCH v5 11/16] x86/sme: Avoid SME/SVE related checks on non-SME/SVE platforms

From: Ard Biesheuvel <ardb@...nel.org>

Reorganize the early SME/SVE init code so that SME/SVE related calls are
deferred until it has been determined that the platform actually
supports this, and so those calls could actually make sense.

This removes logic from the early boot path that executes from the 1:1
mapping when booting a CONFIG_AMD_MEM_ENCRYPT=y kernel on a system that
does not implement that (i.e., 99% of distro kernels)

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/include/asm/mem_encrypt.h | 4 ++--
 arch/x86/kernel/head64.c           | 6 +++---
 arch/x86/mm/mem_encrypt_identity.c | 8 +++-----
 3 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index b31eb9fd5954..b1437ba0b3b8 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -48,7 +48,7 @@ void __init sme_unmap_bootdata(char *real_mode_data);
 void __init sme_early_init(void);
 
 void __init sme_encrypt_kernel(struct boot_params *bp);
-void __init sme_enable(struct boot_params *bp);
+void sme_enable(struct boot_params *bp);
 
 int __init early_set_memory_decrypted(unsigned long vaddr, unsigned long size);
 int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size);
@@ -82,7 +82,7 @@ static inline void __init sme_unmap_bootdata(char *real_mode_data) { }
 static inline void __init sme_early_init(void) { }
 
 static inline void __init sme_encrypt_kernel(struct boot_params *bp) { }
-static inline void __init sme_enable(struct boot_params *bp) { }
+static inline void sme_enable(struct boot_params *bp) { }
 
 static inline void sev_es_init_vc_handling(void) { }
 
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 0b827cbf6ee4..b33f47489505 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -98,9 +98,6 @@ static unsigned long __head sme_postprocess_startup(struct boot_params *bp, pmdv
 	unsigned long vaddr, vaddr_end;
 	int i;
 
-	/* Encrypt the kernel and related (if SME is active) */
-	sme_encrypt_kernel(bp);
-
 	/*
 	 * Clear the memory encryption mask from the .bss..decrypted section.
 	 * The bss section will be memset to zero later in the initialization so
@@ -108,6 +105,9 @@ static unsigned long __head sme_postprocess_startup(struct boot_params *bp, pmdv
 	 * attribute.
 	 */
 	if (sme_get_me_mask()) {
+		/* Encrypt the kernel and related */
+		sme_encrypt_kernel(bp);
+
 		vaddr = (unsigned long)__start_bss_decrypted;
 		vaddr_end = (unsigned long)__end_bss_decrypted;
 
diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index 0166ab1780cc..7ddcf960e92a 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -45,6 +45,7 @@
 #include <asm/sections.h>
 #include <asm/cmdline.h>
 #include <asm/coco.h>
+#include <asm/init.h>
 #include <asm/sev.h>
 
 #include "mm_internal.h"
@@ -502,18 +503,15 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
 	native_write_cr3(__native_read_cr3());
 }
 
-void __init sme_enable(struct boot_params *bp)
+void __head sme_enable(struct boot_params *bp)
 {
 	const char *cmdline_ptr, *cmdline_arg, *cmdline_on;
 	unsigned int eax, ebx, ecx, edx;
 	unsigned long feature_mask;
 	unsigned long me_mask;
 	char buffer[16];
-	bool snp;
 	u64 msr;
 
-	snp = snp_init(bp);
-
 	/* Check for the SME/SEV support leaf */
 	eax = 0x80000000;
 	ecx = 0;
@@ -546,7 +544,7 @@ void __init sme_enable(struct boot_params *bp)
 	feature_mask = (msr & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
 
 	/* The SEV-SNP CC blob should never be present unless SEV-SNP is enabled. */
-	if (snp && !(msr & MSR_AMD64_SEV_SNP_ENABLED))
+	if (snp_init(bp) && !(msr & MSR_AMD64_SEV_SNP_ENABLED))
 		snp_abort();
 
 	/* Check if memory encryption is enabled */
-- 
2.44.0.rc0.258.g7320e95886-goog