linux-kernel - Re: [PATCH v3] x86/fault: Send a SIGBUS to user process always for hwpoison page access.

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Message-Id: <59469ECC-5316-4074-98EF-52FFF7940818@amacapital.net>
Date:   Mon, 1 Mar 2021 11:09:36 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>, Aili Yao <yaoaili@...gsoft.com>,
        HORIGUCHI NAOYA <naoya.horiguchi@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        yangfeng1@...gsoft.com, Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] x86/fault: Send a SIGBUS to user process always for hwpoison page access.



> On Mar 1, 2021, at 11:02 AM, Luck, Tony <tony.luck@...el.com> wrote:
> 
> 
>> 
>> Some programs may use read(2), write(2), etc as ways to check if
>> memory is valid without getting a signal.  They might not want
>> signals, which means that this feature might need to be configurable.
> 
> That sounds like an appalling hack. If users need such a mechanism
> we should create some better way to do that.
> 

Appalling hack or not, it works. So, if we’re going to send a signal to user code that looks like it originated from a bina fide architectural recoverable fault, it needs to be recoverable.  A load from a failed NVDIMM page is such a fault. A *kernel* load is not. So we need to distinguish it somehow.

> An aeon ago ACPI created the RASF table as a way for the OS to
> ask the platform to scan a block of physical memory using the patrol
> scrubber in the memory controller.  I never did anything with it in Linux
> because it was just too complex and didn't know of any use cases.
> 
> Users would want to check virtual addresses. Perhaps some new
> option MADV_CHECKFORPOISON to madvise(2) ?
> 
> -Tony