From: Andy Lutomirski <luto@kernel.org> To: Dan Williams <dan.j.williams@intel.com> Cc: Tony Luck <tony.luck@intel.com>, linux-nvdimm <linux-nvdimm@lists.01.org>, Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Al Viro <viro@zeniv.linux.org.uk>, Thomas Gleixner <tglx@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org> Subject: Re: [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter() Date: Tue, 01 May 2018 23:28:10 +0000 [thread overview] Message-ID: <CALCETrV=HtQDfrKmY0Td2GfxAxZbAoz71JbYSZcq0LxL2A-RqQ@mail.gmail.com> (raw) In-Reply-To: <CAPcyv4jA98NVNqYFpj29OHE45HVp1DMH9oFO4-neWKA_4WKTwA@mail.gmail.com> On Tue, May 1, 2018 at 4:02 PM Dan Williams <dan.j.williams@intel.com> wrote: > On Tue, May 1, 2018 at 2:05 PM, Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > On Tue, May 1, 2018 at 1:55 PM Dan Williams <dan.j.williams@intel.com> > > wrote: > > > >> The result of the bypass is that the kernel treats machine checks during > >> read as system fatal (reboot) when they could simply be flagged as an > >> I/O error, similar to performing reads through the pmem driver. Prevent > >> this fatal condition by deploying memcpy_mcsafe() in the fsdax read > >> path. > > > > How about just changing the rules, and go the old "Don't do that then" way? > > > > IOW, get rid of the whole idea that MCS errors should be fatal. It's wrong > > and pointless anyway. > > > > The while approach seems fundamentally buggered, if you ever want to mmap > > one of these things. And don't you want that? > > > > So why continue down a fundamentally broken path? > I'm confused. Are you talking about getting rid of the block-layer > bypass or changing how MCS errors are handled? If it's the former I've > gotten push back in the past trying to remove the bypass, but I feel > better about my chances to slay that beast wielding the +5 Hammer of > Linus. If it's the latter, MCS error handling, I don't see how get > around something like copy_to_iter_mcsafe(). > You mention mmap. Yes, we want the predominant access model to be > dax-mmap for Persistent Memory, but there's still the question about > what to do with media errors. To date we are trying to mirror the > error handling model for System Memory, i.e. SIGBUS to the process > that consumed the error. Is that error handling model also problematic > in your view? I'm not sure exactly what you mean here, but my understanding of the status quo is that memory errors in user code are non-fatal but that memory errors in kernel code are fatal unless there's an appropriate extable entry. The old iov_iter code assumes that memcpy() on kernel addresses can't fail. I'm not sure how else it could work. _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm
WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto@kernel.org> To: Dan Williams <dan.j.williams@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org>, linux-nvdimm <linux-nvdimm@lists.01.org>, Tony Luck <tony.luck@intel.com>, Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>, X86 ML <x86@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>, Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter() Date: Tue, 01 May 2018 23:28:10 +0000 [thread overview] Message-ID: <CALCETrV=HtQDfrKmY0Td2GfxAxZbAoz71JbYSZcq0LxL2A-RqQ@mail.gmail.com> (raw) In-Reply-To: <CAPcyv4jA98NVNqYFpj29OHE45HVp1DMH9oFO4-neWKA_4WKTwA@mail.gmail.com> On Tue, May 1, 2018 at 4:02 PM Dan Williams <dan.j.williams@intel.com> wrote: > On Tue, May 1, 2018 at 2:05 PM, Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > On Tue, May 1, 2018 at 1:55 PM Dan Williams <dan.j.williams@intel.com> > > wrote: > > > >> The result of the bypass is that the kernel treats machine checks during > >> read as system fatal (reboot) when they could simply be flagged as an > >> I/O error, similar to performing reads through the pmem driver. Prevent > >> this fatal condition by deploying memcpy_mcsafe() in the fsdax read > >> path. > > > > How about just changing the rules, and go the old "Don't do that then" way? > > > > IOW, get rid of the whole idea that MCS errors should be fatal. It's wrong > > and pointless anyway. > > > > The while approach seems fundamentally buggered, if you ever want to mmap > > one of these things. And don't you want that? > > > > So why continue down a fundamentally broken path? > I'm confused. Are you talking about getting rid of the block-layer > bypass or changing how MCS errors are handled? If it's the former I've > gotten push back in the past trying to remove the bypass, but I feel > better about my chances to slay that beast wielding the +5 Hammer of > Linus. If it's the latter, MCS error handling, I don't see how get > around something like copy_to_iter_mcsafe(). > You mention mmap. Yes, we want the predominant access model to be > dax-mmap for Persistent Memory, but there's still the question about > what to do with media errors. To date we are trying to mirror the > error handling model for System Memory, i.e. SIGBUS to the process > that consumed the error. Is that error handling model also problematic > in your view? I'm not sure exactly what you mean here, but my understanding of the status quo is that memory errors in user code are non-fatal but that memory errors in kernel code are fatal unless there's an appropriate extable entry. The old iov_iter code assumes that memcpy() on kernel addresses can't fail. I'm not sure how else it could work.
next prev parent reply other threads:[~2018-05-01 23:28 UTC|newest] Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-05-01 20:45 [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter() Dan Williams 2018-05-01 20:45 ` Dan Williams 2018-05-01 20:45 ` [PATCH 1/6] x86, memcpy_mcsafe: update labels in support of write fault handling Dan Williams 2018-05-01 20:45 ` Dan Williams 2018-05-01 20:45 ` [PATCH 2/6] x86, memcpy_mcsafe: return bytes remaining Dan Williams 2018-05-01 20:45 ` Dan Williams 2018-05-01 20:45 ` [PATCH 3/6] x86, memcpy_mcsafe: add write-protection-fault handling Dan Williams 2018-05-01 20:45 ` Dan Williams 2018-05-01 20:45 ` [PATCH 4/6] x86, memcpy_mcsafe: define copy_to_iter_mcsafe() Dan Williams 2018-05-01 20:45 ` Dan Williams 2018-05-01 22:17 ` kbuild test robot 2018-05-01 22:17 ` kbuild test robot 2018-05-01 22:49 ` kbuild test robot 2018-05-01 22:49 ` kbuild test robot 2018-05-01 20:45 ` [PATCH 5/6] dax: use copy_to_iter_mcsafe() in dax_iomap_actor() Dan Williams 2018-05-01 20:45 ` Dan Williams 2018-05-01 20:45 ` [PATCH 6/6] x86, nfit_test: unit test for memcpy_mcsafe() Dan Williams 2018-05-01 20:45 ` Dan Williams 2018-05-01 21:05 ` [PATCH 0/6] use memcpy_mcsafe() for copy_to_iter() Linus Torvalds 2018-05-01 21:05 ` Linus Torvalds 2018-05-01 23:02 ` Dan Williams 2018-05-01 23:02 ` Dan Williams 2018-05-01 23:28 ` Andy Lutomirski [this message] 2018-05-01 23:28 ` Andy Lutomirski 2018-05-01 23:31 ` Dan Williams 2018-05-01 23:31 ` Dan Williams 2018-05-02 0:09 ` Linus Torvalds 2018-05-02 0:09 ` Linus Torvalds 2018-05-02 2:25 ` Dan Williams 2018-05-02 2:25 ` Dan Williams 2018-05-02 2:53 ` Linus Torvalds 2018-05-02 2:53 ` Linus Torvalds 2018-05-02 3:02 ` Dan Williams 2018-05-02 3:02 ` Dan Williams 2018-05-02 3:13 ` Linus Torvalds 2018-05-02 3:13 ` Linus Torvalds 2018-05-02 3:20 ` Dan Williams 2018-05-02 3:20 ` Dan Williams 2018-05-02 3:22 ` Dan Williams 2018-05-02 3:22 ` Dan Williams 2018-05-02 3:33 ` Linus Torvalds 2018-05-02 3:33 ` Linus Torvalds 2018-05-02 4:00 ` Dan Williams 2018-05-02 4:00 ` Dan Williams 2018-05-02 4:14 ` Linus Torvalds 2018-05-02 4:14 ` Linus Torvalds 2018-05-02 5:37 ` Dan Williams 2018-05-02 5:37 ` Dan Williams 2018-05-02 16:19 ` Andy Lutomirski 2018-05-02 16:19 ` Andy Lutomirski 2018-05-02 17:47 ` Dan Williams 2018-05-02 17:47 ` Dan Williams 2018-05-02 8:30 ` Borislav Petkov 2018-05-02 8:30 ` Borislav Petkov 2018-05-02 13:52 ` Dan Williams 2018-05-02 13:52 ` Dan Williams
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