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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH v3] x86/fault: Send a SIGBUS to user process always for hwpoison page access.
Date:   Mon, 1 Mar 2021 11:09:36 -0800
Message-Id: <59469ECC-5316-4074-98EF-52FFF7940818@amacapital.net>
References: <8d0c76f97f35499f91a2b82d3e7c024d@intel.com>
Cc:     Andy Lutomirski <luto@kernel.org>, Aili Yao <yaoaili@kingsoft.com>,
        HORIGUCHI NAOYA <naoya.horiguchi@nec.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
        yangfeng1@kingsoft.com, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <8d0c76f97f35499f91a2b82d3e7c024d@intel.com>
To:     "Luck, Tony" <tony.luck@intel.com>
Precedence: bulk


> On Mar 1, 2021, at 11:02 AM, Luck, Tony <tony.luck@intel.com> wrote:
>=20
> =EF=BB=BF
>>=20
>> 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.
>=20
> That sounds like an appalling hack. If users need such a mechanism
> we should create some better way to do that.
>=20

Appalling hack or not, it works. So, if we=E2=80=99re going to send a signal=
 to user code that looks like it originated from a bina fide architectural r=
ecoverable fault, it needs to be recoverable.  A load from a failed NVDIMM p=
age is such a fault. A *kernel* load is not. So we need to distinguish it so=
mehow.

> 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.
>=20
> Users would want to check virtual addresses. Perhaps some new
> option MADV_CHECKFORPOISON to madvise(2) ?
>=20
> -Tony