On 23/08/18 13:24, Alexander Graf wrote: > On 08/23/2018 01:16 PM, Marc Zyngier wrote: >> On 21/08/18 17:54, Alexander Graf wrote: >>> On 08/21/2018 05:08 PM, Marc Zyngier wrote: >>>> On 21/08/18 15:08, Alexander Graf wrote: >>>>> On 08/21/2018 03:57 PM, Marc Zyngier wrote: >>>>>> On 21/08/18 14:35, Alexander Graf wrote: >>>>>>> On 10/23/2017 06:11 PM, Marc Zyngier wrote: >>>>>>>> The only case where we actually need to perform a dcache maintenance >>>>>>>> is when we map the page for the first time, and subsequent permission >>>>>>>> faults do not require cache maintenance. Let's make it conditional >>>>>>>> on not being a permission fault (and thus a translation fault). >>>>>>>> >>>>>>>> Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> >>>>>>>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> >>>>>>> This patch unfortunately breaks something on Hi1616 SoCs when running >>>>>>> 32bit guests. With this patch applied (and thus with 4.18) I get random >>>>>>> illegal instruction warnings from 32bit code inside VMs. I do not know >>>>>>> at this point whether this affects other CPUs as well. >>>>>> Can you please give a few more details? >>>>>> >>>>>> - what are the CPUs on this Hi1616? At least a /proc/cpuinfo would help >>>>> These are A72s: >>>>> >>>>> processor : 0 >>>>> BogoMIPS : 100.00 >>>>> Features : fp asimd evtstrm aes pmull sha1 sha2 crc32 cpuid >>>>> CPU implementer : 0x41 >>>>> CPU architecture: 8 >>>>> CPU variant : 0x0 >>>>> CPU part : 0xd08 >>>>> CPU revision : 2 >>>>> >>>>>> - an example of the crash? Is it within the decompressor? After? This >>>>>> things do matter, given the number of crazy things the 32bit kernel does >>>>> They are always in user space. My current reproducer is this: >>>>> >>>>> $ while rpm -qa > /dev/null; do :; done >>>>> >>>>> If I run this in parallel with something that just populates RAM (dd >>>>> if=/dev/nvme0n1 of=/dev/null bs=10G) I get an illegal instruction fault >>>>> within seconds: >>>>> >>>>> sh-4.4# while rpm -qa > /dev/null; do true; done >>>>> Illegal instruction (core dumped) >>>>> >>>>> >>>>>> - a host kernel configuration? >>>>> Host kernel configuration is just the normal openSUSE one: >>>>> >>>>> https://kernel.opensuse.org/cgit/kernel-source/plain/config/arm64/default?h=stable >>>>> >>>>>>> If anyone is interested in a reproducer, I have something handy. But for >>>>>>> now I believe we should just revert this patch. >>>>>> Before we revert anything, I'd like to understand what is happening. >>>>> Yeah, I didn't realize the commit is already in since 4.16, so I agree. >>>>> I'll bisect a bit, but it may take a while. >>>> Do you mind giving this a try? >>>> >>>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c >>>> index 1d90d79706bd..df8f3d5eaa22 100644 >>>> --- a/virt/kvm/arm/mmu.c >>>> +++ b/virt/kvm/arm/mmu.c >>>> @@ -1531,7 +1536,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>>> kvm_set_pfn_dirty(pfn); >>>> } >>>> >>>> - if (fault_status != FSC_PERM) >>>> + if (fault_status != FSC_PERM || write_fault) >>>> clean_dcache_guest_page(pfn, PMD_SIZE); >>>> >>>> if (exec_fault) { >>>> @@ -1553,7 +1558,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>>> mark_page_dirty(kvm, gfn); >>>> } >>>> >>>> - if (fault_status != FSC_PERM) >>>> + if (fault_status != FSC_PERM || write_fault) >>>> clean_dcache_guest_page(pfn, PAGE_SIZE); >>>> >>>> if (exec_fault) { >>>> >>>> >>>> The missing logic is that a write from the guest could have triggered >>>> a CoW, meaning we definitely need to flush it in that case too. It >>>> fixes a kvm-unit-test regression here. >>> This patch unfortunately does not fix the issue. I still see illegal >>> instructions. >> [+Dave] >> >> That's because what you're observing has nothing to do with caching, but >> with FP/SIMD trapping instead. Thanks to the guest image you've provided, >> I've been able to extract the following: >> >> [ 3.944273] systemd-udevd (266): undefined instruction: pc=(ptrval) >> [ 3.945396] CPU: 0 PID: 266 Comm: systemd-udevd Not tainted 4.17.14-2-lpae #1 openSUSE Tumbleweed (unreleased) >> [ 3.947130] Hardware name: Generic DT based system >> [ 3.947976] PC is at 0xb6b9397a >> [ 3.948547] LR is at 0xb6e9a1b0 >> [ 3.958291] pc : [<b6b9397a>] lr : [<b6e9a1b0>] psr: 20070030 >> [ 3.959664] sp : bebe36a0 ip : b6f6ad50 fp : 005e8784 >> [ 3.960601] r10: bebe3814 r9 : bebe36c0 r8 : bebe36bc >> [ 3.961522] r7 : bebe3814 r6 : 00000074 r5 : 00000000 r4 : 00000000 >> [ 3.962661] r3 : 005f2b60 r2 : 00000074 r1 : 00000000 r0 : bebe3814 >> [ 3.963801] Flags: nzCv IRQs on FIQs on Mode USER_32 ISA Thumb Segment user >> [ 4.000606] Control: 30c5383d Table: 6a8e7400 DAC: fffffffd >> [ 4.001659] Code: d1f9 f1a0 0001 4770 (eee0) 1b10 >> >> maz@flakes:~/armv7-build-fail$ (echo .thumb; echo .inst.w 0xeee01b10) > x.S && arm-linux-gnueabihf-gcc -c x.S && arm-linux-gnueabihf-objdump -d x.o >> >> x.o: file format elf32-littlearm >> >> >> Disassembly of section .text: >> >> 00000000 <.text>: >> 0: eee0 1b10 vdup.8 q0, r1 >> >> A VFP instruction. Given that you've reported that things worked in >> 4.17 and broke in 4.18, I strongly suspect the new lazy FPSIMD code. >> Upon inspection, the way we setup trapping for 32bit is a tiny bit >> suspect. >> >> Could you please give this patch a go? My Seattle has been running >> with it for 30 minutes now, and it is still running (instead of >> failing with seconds). >> >> Thanks, >> >> M. >> >> From f2d1d43e2429f9269ab6c565440e095ab3a9be89 Mon Sep 17 00:00:00 2001 >> From: Marc Zyngier <marc.zyngier@xxxxxxx> >> Date: Thu, 23 Aug 2018 11:51:43 +0100 >> Subject: [PATCH] arm64: KVM: Only force FPEXC32_EL2.EN if trapping FPSIMD >> >> If trapping FPSIMD in the context of an AArch32 guest, it is critical >> to set FPEXC32_EL2.EN to 1 so that the trapping is taken to EL2 and >> not EL1. >> >> Conversely, it is just as critical *not* to set FPEXC32_EL2.EN to 1 >> if we're not going to trap FPSIMD, as we then corrupt the existing >> VFP state. >> >> Moving the call to __activate_traps_fpsimd32 to the point where we >> know for sure that we are going to trap ensures that we don't set that >> bit spuriously. >> >> Fixes: e6b673b741ea ("KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing") >> Cc: Dave Martin <dave.martin@xxxxxxx> >> Reported-by: Alexander Graf <agraf@xxxxxxx> >> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> > > Very good catch. This patch does indeed fix it. I'm still puzzled why > reverting the dcache patch actually had any positive effect, but oh well > ... :) Well, there is still a bug in that dcache patch, which I've fixed separately (in a better way than what I sent before), so you may have hit that as well, but that's not the most visible bug. > Tested-by: Alexander Graf <agraf@xxxxxxx> Thanks for that. M. -- Jazz is not dead. It just smells funny...
