[RFC/RFT PATCH] x86/efistub: Don't bother enabling SEV in the EFI stub

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.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.

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

Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dionna Amalie Glaze <dionnaglaze@google.com>
Cc: Kevin Loughlin <kevinloughlin@google.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/include/asm/sev.h              | 2 --
 drivers/firmware/efi/libstub/x86-stub.c | 6 ------
 2 files changed, 8 deletions(-)

I'm still waiting for my SEV-capable hardware to turn up so this was
build tested only.

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 7427eb233990..1db906d6924b 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -442,7 +442,6 @@ 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-
@@ -533,7 +532,6 @@ 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 cafc90d4caaf..52ed13ec4fe9 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -925,12 +925,6 @@ 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);
-- 
2.49.0.604.gff1f9ca942-goog