Re: [PATCH v7 6/6] x86/split_lock: Fix the split lock #AC handling when running as guest

[Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuwamy@linux.intel.com>]

+ Xiaoyao

On 10/13/21 1:30 PM, Sean Christopherson wrote:
> On Tue, Oct 05, 2021, Kuppuswamy Sathyanarayanan wrote:
>> From: Xiaoyao Li <xiaoyao.li@intel.com>
>>
>> If running as guest and hypervisor enables
>> MSR_TEST_CTRL.SPLIT_LOCK_DETECT during its running, it can get split
>> lock #AC even though sld_state is sld_off.
> That's a hypervisor bug, no?  The hypervisor should never inject a fault that
> the guest cannot reasonably expect.
>
>> For kernel mode #AC, it always dies("split lock"), no more action
>> needed.
>>
>> For user mode #AC, it should treat sld_off (default state when feature
>> is not available) as fatal as well.
>>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>> ---
>>   arch/x86/kernel/cpu/intel.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
>> index 01d7935feaed..47f0bc95ce2a 100644
>> --- a/arch/x86/kernel/cpu/intel.c
>> +++ b/arch/x86/kernel/cpu/intel.c
>> @@ -1190,7 +1190,12 @@ static void bus_lock_init(void)
>>   
>>   bool handle_user_split_lock(struct pt_regs *regs, long error_code)
>>   {
>> -	if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
>> +	/*
>> +	 * In virtualization environment, it can get split lock #AC even when
>> +	 * sld_off but hypervisor enables it.
>> +	 * Thus only handles when sld_warn explicitly.
>> +	 */
>> +	if ((regs->flags & X86_EFLAGS_AC) || sld_state != sld_warn)
>>   		return false;
>>   	split_lock_warn(regs->ip);
>>   	return true;
>> -- 
>> 2.25.1
>>
-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer