Date: Sun, 30 Apr 2023 22:31:53 -0500 From: "Jason A. Harmening" <jah@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Dimitry Andric <dim@freebsd.org>, src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-branches@freebsd.org Subject: Re: git: 060699e91369 - stable/13 - Merge llvm-project release/15.x llvmorg-15.0.7-0-g8dfdcc7b7bf6 Message-ID: <ZE8yqfOkrrMddua1@corona> In-Reply-To: <ZE8JJQizER2WrTr2@corona> References: <202304092135.339LZMeJ081640@gitrepo.freebsd.org> <ZE1jEcA7iL3QrbOP@corona> <76DD2CB9-986B-4349-8F46-3B7BF63EB315@FreeBSD.org> <ZE1vtvghEV_RsD2b@corona> <ZE33_AWw0DO8-EjM@kib.kiev.ua> <ZE7-AcTXtCkSzsHb@corona> <ZE8JJQizER2WrTr2@corona>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sun, Apr 30, 2023 at 07:34:45PM -0500, Jason A. Harmening wrote: > On Sun, Apr 30, 2023 at 06:47:13PM -0500, Jason A. Harmening wrote: > > On Sun, Apr 30, 2023 at 08:09:16AM +0300, Konstantin Belousov wrote: > > > On Sat, Apr 29, 2023 at 02:27:50PM -0500, Jason A. Harmening wrote: > > > > On Sat, Apr 29, 2023 at 08:49:28PM +0200, Dimitry Andric wrote: > > > > > On 29 Apr 2023, at 20:33, Jason A. Harmening <jah@FreeBSD.org> wrote: > > > > > > > > > > > > On Sun, Apr 09, 2023 at 09:35:22PM +0000, Dimitry Andric wrote: > > > > > >> The branch stable/13 has been updated by dim: > > > > > >> > > > > > >> URL: https://cgit.FreeBSD.org/src/commit/?id=060699e9136975d51d3f726b9785bdbac9a62ba6 > > > > > >> > > > > > >> commit 060699e9136975d51d3f726b9785bdbac9a62ba6 > > > > > >> Author: Dimitry Andric <dim@FreeBSD.org> > > > > > >> AuthorDate: 2023-01-14 16:33:24 +0000 > > > > > >> Commit: Dimitry Andric <dim@FreeBSD.org> > > > > > >> CommitDate: 2023-04-09 14:54:52 +0000 > > > > > >> > > > > > >> Merge llvm-project release/15.x llvmorg-15.0.7-0-g8dfdcc7b7bf6 > > > > > >> > > > > > >> This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and > > > > > >> openmp to llvmorg-15.0.7-0-g8dfdcc7b7bf6. > > > > > >> > > > > > >> PR: 265425 > > > > > >> MFC after: 2 weeks > > > > > > > > > > > > This MFC of llvm15 appears to have completely broken the Intel IOMMU > > > > > > driver on my stable/13 machine. After this series of commits, any > > > > > > downstream DMA seems to produce an IOMMU translation fault, which > > > > > > renders the machine completely unusable: no nvme boot disk, no usb > > > > > > keyboard, etc. > > > > > > > > > > > > The faults I see look something like this: > > > > > > > > > > > > DMAR4: ahci0: pci0:17:5 sid 8d fault acc 0 adt 0x0 reason 0x3 addr 26000 > > > > > > > > > > > > It's a bit surprising to see a toolchain upgrade produce breakage like > > > > > > this, but that's what git bisect clearly tells me. I wonder if some of > > > > > > the IOMMU control structures might be defined as C bitfields and the new > > > > > > compiler is emitting them differently? Also, was any breakage like this > > > > > > observed when -current was upgraded to llvm15 several months ago? > > > > > > > > > > I haven't heard anything about such breakage, no. > > > > > > > > > > > > > > > > More generally, this is the second time in as many months I've had to > > > > > > deal with IOMMU breakage on -stable. I can't imagine I'm the only > > > > > > person who sees value in running with DMA remapping enabled; do we need > > > > > > a dedicated DMAR-enabled machine in the cluster to smoke-test changes > > > > > > like this? More generally, should we avoid MFCing high-risk changes > > > > > > like this? > > > > > > > > > > Since there were very few bug reports, it was not deemed high risk. > > > > > > > > > > In any case, it would be good to get the bottom of what is causing the > > > > > problem, so is there any way you can isolate which code seems to be > > > > > going "bad"? > > > > > > > > > > For example, if this problem affects code in sys/dev/iommu, is there > > > > > some way you can compile that part with -O1, or with an older version > > > > > of clang (from ports), to see if the problem goes away? > > > > > > > > I did try removing all custom make.conf settings (previously I just had > > > > CPUTYPE?=icelake-server), but that didn't change the behavior. > > > > > > > > Before I try further build tweaks, I'd like to ask if the IOMMU fault > > > > report can provide guidance here? AFAICT all the faults I'm getting > > > > show "reason 0x3". If I'm reading the VT-d spec correctly, FR=0x3 > > > > indicates an invalid context entry, in other words there's something the > > > > hardware doesn't like in the way the address width or pagetable base is > > > > configured for the PCIe requestor. > > > > > > I would start looking at the other direction: might be, there are still some > > > left shifts for int32 values with the shift count > 30, or uint32 with the > > > count > 31. > > > > > > Also might be useful to dump each context entry on creation, it is kept > > > constant after. > > > > I did look over the constants in intel_reg.h, and didn't see anything > > that looked as though it would be susceptible to sign-extension or > > truncation bugs. In the failing case it's much easier for me to catch > > the fault messages than any initialization message, so I instrumented > > the fault handler to get the context entry from the dmar_ctx object > > using the same logic as dmar_map_ctx_entry(), and then dump out the ctx1 > > and ctx2 fields. What I see are messages like: > > > > ... ctx1 0x10013b001 ctx2 0x103 > > > > At first glance these "look right": the P bit is set in ctx1, and the > > rest of the field looks like a valid physical address. ctx2 also > > doesn't have any of the reserved bits set, but in all cases it does have > > AW=3, which would indicate 57-bit AGAW. But when I boot the last > > working kernel, from the revision prior to the llvm15 MFC, I see this in > > dmesg: > > > > ahci0: dmar4 pci0:0:17:5 rid 8d domain 1 mgaw 48 agaw 48 re-mapped > > > > ...all reported devices show 48-bit MGAW/AGAW, so I would expect ctx2 to > > have AW=2. I suspect this may be the source of the fault, but I'm not > > sure how it's getting configured that way, whether it's an issue with > > reading the capability register or something else. > > > > I can confirm that hacking domain_set_agaw() to always use the settings > from sagaw_bits[2] eliminates the faults and at least allows the machine > to boot to single-user mode. I see what's happening now. When I added the hack to always set sagaw_bits[2], I noted that the passed-in MGAW was still 57, while unit->hw_cap had the correct value of 0x4 (=> 4-level paging, 48-bit AW) in bits 12:8. The problem is that sagaw_bits has agaw=64 in its last entry. This results in dmar_maxaddr2mgaw() attempting a comparison against 1ULL << 64 in the final iteration of its first loop. I suspect the new compiler probably determines that last iteration is meaningless and simply omits it from the (probably unrolled) loop. Since the "loop" terminates with i < nitems(sagaw_bits), the subsequent "allow_less ..." case doesn't execute and we end up erroneously selecting a 57-bit address width. Just commenting out that last entry in sagaw_bits fixes the problem. So, two questions: 1) Does any VT-d hardware actually support 6-level paging? The ca. 2021 VT-d spec I'm looking at indicates 5-level is the greatest depth supported, with everything above that being reserved. 2) I'd expect clang to try very hard to error out in a situation like this, but I see that sys/conf/kern.mk sets -Wno-shift-count-overflow among other things, and more of them were added for clang 15. This seems like a really bad idea, regardless of how much of a PITA it may be to fix these warnings.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?ZE8yqfOkrrMddua1>