Re: [PATCH v1 1/4] x86/fred: Parse cmdline param "fred=" in cpu_parse_early_param()

[Xin Li <xin@zytor.com>]

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.