Date: Sun, 13 Nov 2016 01:13:24 -0700 From: Warner Losh <wlosh@bsdimp.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Warner Losh <imp@bsdimp.com>, Adrian Chadd <adrian.chadd@gmail.com>, "freebsd-mips@freebsd.org" <freebsd-mips@freebsd.org>, Juli Mallett <jmallett@freebsd.org> Subject: Re: svn commit: r307626 - head/sys/ufs/ffs Message-ID: <71C512CD-0FB6-40D8-B46C-30467A245693@bsdimp.com> In-Reply-To: <20161113075557.GH54029@kib.kiev.ua> References: <201610191109.u9JB9TTC002727@repo.freebsd.org> <CAJ-Vmom5rYe89m7bch4qoHHq3X2e67pPk_7G2aRGrjSPNp5mzg@mail.gmail.com> <20161113065851.GD54029@kib.kiev.ua> <CANCZdfreg9wD-2pdGtzgeO86BptSE4M7LnLFTC09K3RHyHR8cQ@mail.gmail.com> <20161113071911.GF54029@kib.kiev.ua> <CANCZdfpC6smeNSPKzpbX8aAnF8CZ%2BSEFQmQ74jqvWUVXrttM%2BQ@mail.gmail.com> <20161113075557.GH54029@kib.kiev.ua>
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[-- Attachment #1 --] [[ Moved to freebsd-mips and cc’d to Juli ]] > On Nov 13, 2016, at 12:55 AM, Konstantin Belousov <kostikbel@gmail.com> wrote: > > On Sun, Nov 13, 2016 at 12:33:57AM -0700, Warner Losh wrote: >> On Sun, Nov 13, 2016 at 12:19 AM, Konstantin Belousov >> <kostikbel@gmail.com> wrote: >>> On Sun, Nov 13, 2016 at 12:12:02AM -0700, Warner Losh wrote: >>>> On Sat, Nov 12, 2016 at 11:58 PM, Konstantin Belousov >>>> <kostikbel@gmail.com> wrote: >>>>> On Sat, Nov 12, 2016 at 03:19:13PM -0800, Adrian Chadd wrote: >>>>>> hi! >>>>>> >>>>>> This broke freebsd on mips24k. >>>>>> >>>>>> BAD_PAGE_FAULT: pid 1 tid 100001 (init), uid 0: pc 0x4002a4 got a read >>>>>> fault (type 0x2) at 0 >>>>>> Trapframe Register Dump: >>>>>> zero: 0 at: 0 v0: 0 v1: 0 >>>>>> a0: 0x7fffeecc a1: 0 a2: 0 a3: 0 >>>>>> t0: 0 t1: 0 t2: 0 t3: 0 >>>>>> t4: 0 t5: 0 t6: 0 t7: 0 >>>>>> t8: 0 t9: 0x400260 s0: 0x10 s1: 0x2 >>>>>> s2: 0x7fffeed0 s3: 0 s4: 0 s5: 0 >>>>>> s6: 0 s7: 0 k0: 0 k1: 0 >>>>>> gp: 0x4d55d0 sp: 0x7ffeee90 s8: 0 ra: 0 >>>>>> sr: 0xfc13 mullo: 0 mulhi: 0 badvaddr: 0 >>>>>> cause: 0x8 pc: 0x4002a4 >>>>>> Page table info for pc address 0x4002a4: pde = 0x809be000, pte = 0xa001acda >>>>>> Dumping 4 words starting at pc address 0x4002a4: >>>>>> 8c420000 14400003 00908021 8f828024 >>>>>> Page table info for bad address 0: pde = 0, pte = 0 >>>>> MIPS24k has split I/D caches, and both are VIPT, am I right ? >>>>> I was not able to find the handling of cache aliasing in mips/pmap.c. >>>>> >>>>> Still, I am curious whether setting the loader tunable vfs.buf_pager_relbuf >>>>> to 1 change anything. >>>> >>>> MIPS caches are such that creating two virtual mappings to the same >>>> physical page will cause corruption. It's simply not allowed, at least >>>> for the class of MIPS machines I used to bring up the port originally. >>> >>> Yes, caches are VIPT on 24k, according to the "MIPS32(R) 24K(R) >>> Processor Core Family Software User's Manual " rev 3.11. My question is, >>> how is that handled in the mips pmap.c. I was not able to locate >>> the alias detection and prevention code, or e.g. switching to uncached mode >>> for the page when aliasing is detected, after browsing pmap. >> >> Aliases are not permitted. IIRC, there's no code that detects this >> condition. One must simply never ever have multiple cached mappings of >> a page at once. A quick glance at the code doesn't locate anything. > Then, the obvious next question is what does prevent such aliased > mappings ? Not only usermode might establish such situation by > double-mapping, but also e.g. our coherent buffer/page cache maps page > into KVA and the same page might be mapped into usermode. The later > situation is my current thought about possible cause of the reported > init(8) fault. That’s a very good question. Unfortunately my memory here fails me. I have a recollection that the various cache flushing that we do in the map ensures that we don’t hit a problem. However, I couldn’t construct a coherent answer to where this takes place after a brief look at the code. Multiple mappings will cause data corruption though. I wouldn’t have thought it causes the fault in question, but MIPS errors can manifest in strange ways, so perhaps you are correct. I don’t get how the fault address is 0 though from that scenario. Maybe Adrian can recall. Or Juli can help. Warner [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJYKCClAAoJEGwc0Sh9sBEAIOsQAKWRViXd09yNuv77TI9EKmZi dqnuwrLBy8iuqQMvUQVvmEs/miOBarVZt/4HdrAaij3ruvDwK9XqbRZc8zs2UGI6 Ep5dAzuAXZr7hMJXFSr+5zlCdNaPui85AYCbOqcEEuZ34NNRrE4b3hPUsBd9dcMR ZCDu2wVlWhpZtsCJNohF/4SohU8W2qo7ZCSlpckR04yNsaQX+sxkwRopRGFSs101 wUihLKTto4Kj7Bhvpv8Up79AyIC9HelpZBPhTKOgq777YGrPlJdr1p7yKPfFogKh H+oVbKn+6mPcAYJ0845yz9x2l34WDgxzAKGoDacpPo5+n2W/oFx7uiifHx0j20Ak YYKSDcn/+MjgTGEargqSWxrFORJYhIDVromlMVBq81ENxLbT71xS6NUVczh/EJrr vv3RxBWbk2q05fzCaWzJVc/9f70JXfgwbWMhsn0Bv/NhC3SDrcd2teCTHBZAfCIn j1GlHpmA6pknwVK1lm9NBjeAhpG29jsttizr7C9TiRwOH3aNIBG27/KExSwHDGhz QYht1kp8yYdu6djsTbI+7mTEEWV5fv7qWw6NBHO0sM/GH3GstNNaP4Gw74XHq7Zi pp4tMFi/qacOSazYa+03E8B7Pi5K2vUt7c76kjTYzp3AQnsOglVUzE97LkRNDvIr VVtGxz3BG0UyepWmZoNr =fUMb -----END PGP SIGNATURE-----
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