linux-kernel - Re: [PATCH v2 3/5] x86/mce: add EX_TYPE_EFAULT_REG as in-kernel recovery context to fix copy-from-user operations regression

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Message-ID: <88a674d7-4898-4bdd-aba9-65019bc5bb8c@linux.alibaba.com>
Date: Tue, 18 Feb 2025 22:03:02 +0800
From: Shuai Xue <xueshuai@...ux.alibaba.com>
To: Peter Zijlstra <peterz@...radead.org>, Borislav Petkov <bp@...en8.de>
Cc: tony.luck@...el.com, bp@...en8.de, nao.horiguchi@...il.com,
 tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
 x86@...nel.org, hpa@...or.com, linmiaohe@...wei.com,
 akpm@...ux-foundation.org, jpoimboe@...nel.org, linux-edac@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 baolin.wang@...ux.alibaba.com, tianruidong@...ux.alibaba.com
Subject: Re: [PATCH v2 3/5] x86/mce: add EX_TYPE_EFAULT_REG as in-kernel
 recovery context to fix copy-from-user operations regression



在 2025/2/18 21:02, Peter Zijlstra 写道:
> On Tue, Feb 18, 2025 at 01:54:08PM +0100, Peter Zijlstra wrote:
> 
>> ---
>> diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
>> index dac4d64dfb2a..cb021058165f 100644
>> --- a/arch/x86/kernel/cpu/mce/severity.c
>> +++ b/arch/x86/kernel/cpu/mce/severity.c
>> @@ -300,13 +300,12 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)
>>   	copy_user  = is_copy_from_user(regs);
>>   	instrumentation_end();
>>   
>> -	switch (fixup_type) {
>> -	case EX_TYPE_UACCESS:
>> -		if (!copy_user)
>> -			return IN_KERNEL;
>> -		m->kflags |= MCE_IN_KERNEL_COPYIN;
>> -		fallthrough;
>> +	if (copy_user) {
>> +		m->kflags |= MCE_IN_KERNEL_COPYIN | MCE_IN_KERNEL_COPYIN;
> 
> Typing is hard, obviously that second should'be been _RECOV.

Hah, it doesn't matter, I got your point.

> 
>> +		return IN_KERNEL_RECOV
> 
> But why are we having that bit *and* a return value saying the same
> thing?

Yes, it is rather redundant. I can refactor this out if @Borislav is
happy with that.

> 
>> +	}
>>   
>> +	switch (fixup_type) {
>>   	case EX_TYPE_FAULT_MCE_SAFE:
>>   	case EX_TYPE_DEFAULT_MCE_SAFE:
>>   		m->kflags |= MCE_IN_KERNEL_RECOV;

Thanks.
Shuai