linux-kernel - [PATCH v2 1/7] x86/boot: Remove verify_cpu() from secondary_startup

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Message-ID: <20230116143645.589522290@infradead.org>
Date:   Mon, 16 Jan 2023 15:25:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, Joan Bruguera <joanbrugueram@...il.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        Juergen Gross <jgross@...e.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Jan Beulich <jbeulich@...e.com>,
        Roger Pau Monne <roger.pau@...rix.com>,
        Kees Cook <keescook@...omium.org>, mark.rutland@....com,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Jörg Rödel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>, jroedel@...e.de
Subject: [PATCH v2 1/7] x86/boot: Remove verify_cpu() from secondary_startup_64()

The boot trampolines from trampoline_64.S have code flow like:

  16bit BIOS			SEV-ES				64bit EFI

  trampoline_start()		sev_es_trampoline_start()	trampoline_start_64()
    verify_cpu()			  |				|
  switch_to_protected:    <---------------'				v
       |							pa_trampoline_compat()
       v								|
  startup_32()		<-----------------------------------------------'
       |
       v
  startup_64()
       |
       v
  tr_start() := head_64.S:secondary_startup_64()

Since AP bringup always goes through the 16bit BIOS path (EFI doesn't
touch the APs), there is already a verify_cpu() invocation.

Removing the verify_cpu() invocation from secondary_startup_64()
renders the whole secondary_startup_64_no_verify() thing moot, so
remove that too.

Cc: jroedel@...e.de
Cc: hpa@...or.com
Fixes: e81dc127ef69 ("x86/callthunks: Add call patching for call depth tracking")
Reported-by: Joan Bruguera <joanbrugueram@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/realmode.h |    1 -
 arch/x86/kernel/head_64.S       |   16 ----------------
 arch/x86/realmode/init.c        |    6 ------
 3 files changed, 23 deletions(-)

--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -73,7 +73,6 @@ extern unsigned char startup_32_smp[];
 extern unsigned char boot_gdt[];
 #else
 extern unsigned char secondary_startup_64[];
-extern unsigned char secondary_startup_64_no_verify[];
 #endif
 
 static inline size_t real_mode_size_needed(void)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -143,22 +143,6 @@ SYM_CODE_START(secondary_startup_64)
 	 * after the boot processor executes this code.
 	 */
 
-	/* Sanitize CPU configuration */
-	call verify_cpu
-
-	/*
-	 * The secondary_startup_64_no_verify entry point is only used by
-	 * SEV-ES guests. In those guests the call to verify_cpu() would cause
-	 * #VC exceptions which can not be handled at this stage of secondary
-	 * CPU bringup.
-	 *
-	 * All non SEV-ES systems, especially Intel systems, need to execute
-	 * verify_cpu() above to make sure NX is enabled.
-	 */
-SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
-	UNWIND_HINT_EMPTY
-	ANNOTATE_NOENDBR
-
 	/*
 	 * Retrieve the modifier (SME encryption mask if SME is active) to be
 	 * added to the initial pgdir entry that will be programmed into CR3.
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -74,12 +74,6 @@ static void __init sme_sev_setup_real_mo
 		th->flags |= TH_FLAGS_SME_ACTIVE;
 
 	if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) {
-		/*
-		 * Skip the call to verify_cpu() in secondary_startup_64 as it
-		 * will cause #VC exceptions when the AP can't handle them yet.
-		 */
-		th->start = (u64) secondary_startup_64_no_verify;
-
 		if (sev_es_setup_ap_jump_table(real_mode_header))
 			panic("Failed to get/update SEV-ES AP Jump Table");
 	}