linux-kernel - [PATCH v3 5/5] x86/efistub: Don't bother enabling SEV in the EFI stub

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Message-ID: <20250422100728.208479-12-ardb+git@google.com>
Date: Tue, 22 Apr 2025 12:07:34 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-efi@...r.kernel.org
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, mingo@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>, Tom Lendacky <thomas.lendacky@....com>, 
	Borislav Petkov <bp@...en8.de>, Dionna Amalie Glaze <dionnaglaze@...gle.com>, 
	Kevin Loughlin <kevinloughlin@...gle.com>
Subject: [PATCH v3 5/5] x86/efistub: Don't bother enabling SEV in the EFI stub

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

One of the last things the EFI stub does before handing over to the core
kernel when booting as a SEV guest is enabling SEV, even though this is
mostly redundant: one of the first things the core kernel does is
calling sme_enable(), after setting up the early GDT and IDT but before
even setting up the kernel page tables. sme_enable() performs the same
SEV-SNP initialization that the decompressor performs in sev_enable().

So let's just drop this call to sev_enable(), and rely on the core
kernel to initiaize SEV correctly.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/include/asm/sev.h              | 2 --
 drivers/firmware/efi/libstub/x86-stub.c | 6 ------
 2 files changed, 8 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 8637a65973ef..d762cc0fd47e 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -443,7 +443,6 @@ static __always_inline void sev_es_nmi_complete(void)
 		__sev_es_nmi_complete();
 }
 extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
-extern void sev_enable(struct boot_params *bp);
 
 /*
  * RMPADJUST modifies the RMP permissions of a page of a lesser-
@@ -531,7 +530,6 @@ static inline void sev_es_ist_exit(void) { }
 static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { return 0; }
 static inline void sev_es_nmi_complete(void) { }
 static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
-static inline void sev_enable(struct boot_params *bp) { }
 static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate) { return 0; }
 static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long attrs) { return 0; }
 static inline void setup_ghcb(void) { }
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index d9ae1a230d39..6b4f5ac91e7f 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -936,12 +936,6 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
 		goto fail;
 	}
 
-	/*
-	 * Call the SEV init code while still running with the firmware's
-	 * GDT/IDT, so #VC exceptions will be handled by EFI.
-	 */
-	sev_enable(boot_params);
-
 	efi_5level_switch();
 
 	enter_kernel(kernel_entry, boot_params);
-- 
2.49.0.805.g082f7c87e0-goog