linux-kernel - [tip: x86/fred] x86/fred: Parse cmdline param "fred=" in cpu_parse_early

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Message-ID: <172357940564.2215.7241066302191703798.tip-bot2@tip-bot2>
Date: Tue, 13 Aug 2024 20:03:25 -0000
From: "tip-bot2 for Xin Li (Intel)" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Hou Wenlong <houwenlong.hwl@...group.com>,
 Thomas Gleixner <tglx@...utronix.de>, "Xin Li (Intel)" <xin@...or.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/fred] x86/fred: Parse cmdline param "fred=" in
 cpu_parse_early_param()

The following commit has been merged into the x86/fred branch of tip:

Commit-ID:     989b5cfaa7b6054f4e1bde914470ee091c23e6a5
Gitweb:        https://git.kernel.org/tip/989b5cfaa7b6054f4e1bde914470ee091c23e6a5
Author:        Xin Li (Intel) <xin@...or.com>
AuthorDate:    Tue, 09 Jul 2024 08:40:46 -07:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Tue, 13 Aug 2024 21:59:21 +02:00

x86/fred: Parse cmdline param "fred=" in cpu_parse_early_param()

Depending on whether FRED is enabled, sysvec_install() installs a system
interrupt handler into either into FRED's system vector dispatch table or
into the IDT.

However FRED can be disabled later in trap_init(), after sysvec_install()
has been invoked already; e.g., the HYPERVISOR_CALLBACK_VECTOR handler is
registered with sysvec_install() in kvm_guest_init(), which is called in
setup_arch() but way before trap_init().

IOW, there is a gap between FRED is available and available but disabled.
As a result, when FRED is available but disabled, early sysvec_install()
invocations fail to install the IDT handler resulting in spurious
interrupts.

Fix it by parsing cmdline param "fred=" in cpu_parse_early_param() to
ensure that FRED is disabled before the first sysvec_install() incovations.

Fixes: 3810da12710a ("x86/fred: Add a fred= cmdline param")
Reported-by: Hou Wenlong <houwenlong.hwl@...group.com>
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Xin Li (Intel) <xin@...or.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/all/20240709154048.3543361-2-xin@zytor.com

---
 arch/x86/kernel/cpu/common.c |  5 +++++
 arch/x86/kernel/traps.c      | 26 --------------------------
 2 files changed, 5 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d4e539d..10a5402 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1510,6 +1510,11 @@ static void __init cpu_parse_early_param(void)
 	if (cmdline_find_option_bool(boot_command_line, "nousershstk"))
 		setup_clear_cpu_cap(X86_FEATURE_USER_SHSTK);
 
+	/* Minimize the gap between FRED is available and available but disabled. */
+	arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg));
+	if (arglen != 2 || strncmp(arg, "on", 2))
+		setup_clear_cpu_cap(X86_FEATURE_FRED);
+
 	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
 	if (arglen <= 0)
 		return;
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4fa0b17..6afb41e 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1402,34 +1402,8 @@ DEFINE_IDTENTRY_SW(iret_error)
 }
 #endif
 
-/* Do not enable FRED by default yet. */
-static bool enable_fred __ro_after_init = false;
-
-#ifdef CONFIG_X86_FRED
-static int __init fred_setup(char *str)
-{
-	if (!str)
-		return -EINVAL;
-
-	if (!cpu_feature_enabled(X86_FEATURE_FRED))
-		return 0;
-
-	if (!strcmp(str, "on"))
-		enable_fred = true;
-	else if (!strcmp(str, "off"))
-		enable_fred = false;
-	else
-		pr_warn("invalid FRED option: 'fred=%s'\n", str);
-	return 0;
-}
-early_param("fred", fred_setup);
-#endif
-
 void __init trap_init(void)
 {
-	if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred)
-		setup_clear_cpu_cap(X86_FEATURE_FRED);
-
 	/* Init cpu_entry_area before IST entries are set up */
 	setup_cpu_entry_areas();