From: Tong Tiangen <tongtiangen@huawei.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Robin Murphy <robin.murphy@arm.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>, <x86@kernel.org>,
"H . Peter Anvin" <hpa@zytor.com>,
<linuxppc-dev@lists.ozlabs.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
Kefeng Wang <wangkefeng.wang@huawei.com>,
Xie XiuQi <xiexiuqi@huawei.com>, Guohanjun <guohanjun@huawei.com>
Subject: Re: [PATCH -next v5 6/8] arm64: add support for machine check error safe
Date: Mon, 20 Jun 2022 09:53:26 +0800 [thread overview]
Message-ID: <95ae5d1a-fcfd-9106-4b13-9978de1a3d23@huawei.com> (raw)
In-Reply-To: <Yq3KiDN87pd6mg+m@FVFF77S0Q05N>
在 2022/6/18 20:52, Mark Rutland 写道:
> On Sat, Jun 18, 2022 at 05:18:55PM +0800, Tong Tiangen wrote:
>> 在 2022/6/17 16:55, Mark Rutland 写道:
>>> On Sat, May 28, 2022 at 06:50:54AM +0000, Tong Tiangen wrote:
>>>> +static bool arm64_do_kernel_sea(unsigned long addr, unsigned int esr,
>>>> + struct pt_regs *regs, int sig, int code)
>>>> +{
>>>> + if (!IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC))
>>>> + return false;
>>>> +
>>>> + if (user_mode(regs) || !current->mm)
>>>> + return false;
>>>
>>> What's the `!current->mm` check for? >>
>> At first, I considered that only user processes have the opportunity to
>> recover when they trigger memory error.
>>
>> But it seems that this restriction is unreasonable. When the kernel thread
>> triggers memory error, it can also be recovered. for instance:
>>
>> https://lore.kernel.org/linux-mm/20220527190731.322722-1-jiaqiyan@google.com/
>>
>> And i think if(!current->mm) shoud be added below:
>>
>> if(!current->mm) {
>> set_thread_esr(0, esr);
>> arm64_force_sig_fault(...);
>> }
>> return true;
>
> Why does 'current->mm' have anything to do with this, though?
Sorry, typo, my original logic was:
if(current->mm) {
[...]
}
>
> There can be kernel threads with `current->mm` set in unusual circumstances
> (and there's a lot of kernel code out there which handles that wrong), so if
> you want to treat user tasks differently, we should be doing something like
> checking PF_KTHREAD, or adding something like an is_user_task() helper.
>
OK, i do want to treat user tasks differently here and didn't take into
account what you said. will be fixed next version according to your
suggestiong.
As follows:
if (!(current->flags & PF_KTHREAD)) {
set_thread_esr(0, esr);
arm64_force_sig_fault(...);
}
return true;
> [...]
>
>>>> +
>>>> + if (apei_claim_sea(regs) < 0)
>>>> + return false;
>>>> +
>>>> + if (!fixup_exception_mc(regs))
>>>> + return false;
>>>
>>> I thought we still wanted to signal the task in this case? Or do you expect to
>>> add that into `fixup_exception_mc()` ?
>>
>> Yeah, here return false and will signal to task in do_sea() ->
>> arm64_notify_die().
>
> I mean when we do the fixup.
>
> I thought the idea was to apply the fixup (to stop the kernel from crashing),
> but still to deliver a fatal signal to the user task since we can't do what the
> user task asked us to.
>
Yes, that's what i mean. :)
>>>> +
>>>> + set_thread_esr(0, esr);
>>>
>>> Why are we not setting the address? Is that deliberate, or an oversight?
>>
>> Here set fault_address to 0, i refer to the logic of arm64_notify_die().
>>
>> void arm64_notify_die(...)
>> {
>> if (user_mode(regs)) {
>> WARN_ON(regs != current_pt_regs());
>> current->thread.fault_address = 0;
>> current->thread.fault_code = err;
>>
>> arm64_force_sig_fault(signo, sicode, far, str);
>> } else {
>> die(str, regs, err);
>> }
>> }
>>
>> I don't know exactly why and do you know why arm64_notify_die() did this? :)
>
> To be honest, I don't know, and that looks equally suspicious to me.
>
> Looking at the git history, that was added in commit:
>
> 9141300a5884b57c ("arm64: Provide read/write fault information in compat signal handlers")
>
> ... so maybe Catalin recalls why.
>
> Perhaps the assumption is just that this will be fatal and so unimportant? ...
> but in that case the same logic would apply to the ESR value, so it's not clear
> to me.
OK, let's proceed as set to 0, if there is any change later, the two
positions shall be changed together.
Thanks,
Tong.
>
> Mark.
>
> .
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next prev parent reply other threads:[~2022-06-20 1:55 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-28 6:50 [PATCH -next v5 0/8]arm64: add machine check safe support Tong Tiangen
2022-05-28 6:50 ` [PATCH -next v5 1/8] arm64: extable: add new extable type EX_TYPE_KACCESS_ERR_ZERO support Tong Tiangen
2022-06-17 8:23 ` Mark Rutland
2022-06-18 2:44 ` Tong Tiangen
2022-05-28 6:50 ` [PATCH -next v5 2/8] arm64: extable: make uaaccess helper use extable type EX_TYPE_UACCESS_ERR_ZERO Tong Tiangen
2022-06-17 8:24 ` Mark Rutland
2022-06-18 3:26 ` Tong Tiangen
2022-06-18 8:42 ` Tong Tiangen
2022-06-18 12:40 ` Mark Rutland
2022-06-20 2:59 ` Tong Tiangen
2022-06-20 9:10 ` Mark Rutland
2022-06-20 13:32 ` Tong Tiangen
2022-06-20 14:13 ` Tong Tiangen
2022-06-20 14:26 ` Mark Rutland
2022-05-28 6:50 ` [PATCH -next v5 3/8] arm64: extable: move _cond_extable to _cond_uaccess_extable Tong Tiangen
2022-06-17 8:31 ` Mark Rutland
2022-05-28 6:50 ` [PATCH -next v5 4/8] arm64: extable: cleanup redundant extable type EX_TYPE_FIXUP Tong Tiangen
2022-06-17 8:43 ` Mark Rutland
2022-05-28 6:50 ` [PATCH -next v5 5/8] Add generic fallback version of copy_mc_to_user() Tong Tiangen
2022-05-28 6:50 ` [PATCH -next v5 6/8] arm64: add support for machine check error safe Tong Tiangen
2022-06-17 8:55 ` Mark Rutland
2022-06-18 9:18 ` Tong Tiangen
2022-06-18 12:52 ` Mark Rutland
2022-06-20 1:53 ` Tong Tiangen [this message]
2022-05-28 6:50 ` [PATCH -next v5 7/8] arm64: add uaccess to machine check safe Tong Tiangen
2022-06-17 9:06 ` Mark Rutland
2022-06-18 9:27 ` Tong Tiangen
2022-06-18 11:35 ` Mark Rutland
2022-06-20 2:04 ` Tong Tiangen
2022-05-28 6:50 ` [PATCH -next v5 8/8] arm64: add cow " Tong Tiangen
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