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[67.180.165.146]) by smtp.gmail.com with ESMTPSA id d1sm148710pjc.24.2021.03.01.11.09.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Mar 2021 11:09:38 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) 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 , Aili Yao , HORIGUCHI NAOYA , Dave Hansen , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , X86 ML , yangfeng1@kingsoft.com, Linux-MM , LKML In-Reply-To: <8d0c76f97f35499f91a2b82d3e7c024d@intel.com> To: "Luck, Tony" X-Mailer: iPhone Mail (18D52) X-Stat-Signature: obbgp4fkyj9y836uddknme8an3hm7fth X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 8244FC000C66 Received-SPF: none (amacapital.net>: No applicable sender policy available) receiver=imf14; identity=mailfrom; envelope-from=""; helo=mail-pg1-f173.google.com; client-ip=209.85.215.173 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614625771-541105 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Mar 1, 2021, at 11:02 AM, Luck, Tony 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