Depending on whether FRED will be used, sysvec_install() installs
a system interrupt handler into FRED system vector dispatch table
or IDT.  However FRED can be disabled later in trap_init(), after
sysvec_install() is called.  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, its IDT handler
is not installed thus spurious_interrupt() will be invoked.

Fix it by parsing cmdline param "fred=" in cpu_parse_early_param()
to minimize the gap between FRED is available and available but
disabled.

Fixes: 3810da12710a ("x86/fred: Add a fred= cmdline param")
Reported-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li (Intel) <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 d4e539d4e158..9a904fe7c829 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 != strlen("on") || strcmp(arg, "on"))
+		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 4fa0b17e5043..6afb41e6cbbb 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();
 
-- 
2.45.2

On 3.07.24 г. 11:54 ч., Xin Li (Intel) wrote:
> Depending on whether FRED will be used, sysvec_install() installs
> a system interrupt handler into FRED system vector dispatch table
> or IDT.  However FRED can be disabled later in trap_init(), after
> sysvec_install() is called.  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, its IDT handler
> is not installed thus spurious_interrupt() will be invoked.
> 
> Fix it by parsing cmdline param "fred=" in cpu_parse_early_param()
> to minimize the gap between FRED is available and available but
> disabled.
> 
> Fixes: 3810da12710a ("x86/fred: Add a fred= cmdline param")
> Reported-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Xin Li (Intel) <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 d4e539d4e158..9a904fe7c829 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 != strlen("on") || strcmp(arg, "on"))


Just make this check :

ret = cmdline_find_option(...)
if (ret < 0 || strcmp()))

A lot more straightforward

> +		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 4fa0b17e5043..6afb41e6cbbb 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();
>   

On 7/4/2024 4:20 AM, Nikolay Borisov wrote:
> 
> 
> On 3.07.24 г. 11:54 ч., Xin Li (Intel) wrote:
>> Depending on whether FRED will be used, sysvec_install() installs
>> a system interrupt handler into FRED system vector dispatch table
>> or IDT.  However FRED can be disabled later in trap_init(), after
>> sysvec_install() is called.  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, its IDT handler
>> is not installed thus spurious_interrupt() will be invoked.
>>
>> Fix it by parsing cmdline param "fred=" in cpu_parse_early_param()
>> to minimize the gap between FRED is available and available but
>> disabled.
>>
>> Fixes: 3810da12710a ("x86/fred: Add a fred= cmdline param")
>> Reported-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
>> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
>> Signed-off-by: Xin Li (Intel) <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 d4e539d4e158..9a904fe7c829 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 != strlen("on") || strcmp(arg, "on"))
> 
> 
> Just make this check :
> 
> ret = cmdline_find_option(...)
> if (ret < 0 || strcmp()))
> 
> A lot more straightforward
> 

I'd do
	if (arglen != 2 || strncmp(arg, "on", 2))

If arglen is 2, strncmp(arg, "on", 2) is essentially strcmp(arg, "on"), 
but I should've kept using strncmp.