Ok, I rebuilt the host kernel with latest linus+tip/master and my queue. The guest kernel is v3.15-8992-g08f7cc749389 with a is a bunch of RAS patches. Before I start doing the coarse-grained bisection by testing -rcs and major numbers, I wanted to catch a #DF and try to analyze at least why it happens. And from what I'm seeing, it looks insane. Ok, so kvm_amd.ko is loaded with npt=0 so that I can see the pagefaults in the trace. All TPs in events/kvm/ are enabled. The df tracepoint is straightforward, attached. However, with npt=0 this #DF TP doesn't get hit. I still can see the #DF though and here's what it looks like. (qemu is latest from git): So let's comment on what I'm seeing: ... qemu-system-x86-20240 [006] d..2 9406.484041: kvm_entry: vcpu 1 qemu-system-x86-20240 [006] d..2 9406.484042: kvm_exit: reason PF excp rip 0xffffffff8103be46 info b ffffffffff5fd380 qemu-system-x86-20240 [006] ...1 9406.484042: kvm_page_fault: address ffffffffff5fd380 error_code b qemu-system-x86-20240 [006] ...1 9406.484044: kvm_emulate_insn: 0:ffffffff8103be46:89 b7 00 d0 5f ff (prot64) qemu-system-x86-20240 [006] ...1 9406.484044: vcpu_match_mmio: gva 0xffffffffff5fd380 gpa 0xfee00380 Write GVA qemu-system-x86-20240 [006] ...1 9406.484044: kvm_mmio: mmio write len 4 gpa 0xfee00380 val 0x39884 qemu-system-x86-20240 [006] ...1 9406.484045: kvm_apic: apic_write APIC_TMICT = 0x39884 qemu-system-x86-20239 [004] d..2 9406.484046: kvm_entry: vcpu 0 qemu-system-x86-20240 [006] d..2 9406.484048: kvm_entry: vcpu 1 qemu-system-x86-20239 [004] d..2 9406.484052: kvm_exit: reason PF excp rip 0xffffffff812da4ff info 0 1188808 this rip is ffffffff812da4e0 <__get_user_8>: ... ffffffff812da4ff: 48 8b 50 f9 mov -0x7(%rax),%rdx so we're basically pagefaulting when doing get_user and the user address is 1188808. And that looks ok, this value is exitinfo2 where SVM puts the faulting address on an #PF exception intercept. qemu-system-x86-20239 [004] ...1 9406.484053: kvm_page_fault: address 1188808 error_code 0 qemu-system-x86-20240 [006] d..2 9406.484055: kvm_exit: reason write_cr3 rip 0xffffffff816112d0 info 8000000000000000 0 This is interesting, cpu1 switches address spaces, looks like we're in context_switch(), i.e. consistent with the guest rip pointing to __schedule+0x28f below. I say "interesting" because this bug feels like we're trying to access the user process' memory which is gone by the time we do so. Hmm, just a gut feeling though. qemu-system-x86-20239 [004] d..2 9406.484059: kvm_entry: vcpu 0 qemu-system-x86-20239 [004] d..2 9406.484060: kvm_exit: reason PF excp rip 0xffffffff812da4ff info 0 1188808 qemu-system-x86-20239 [004] ...1 9406.484061: kvm_page_fault: address 1188808 error_code 0 Now here's where it gets interesting: qemu-system-x86-20239 [004] d..2 9406.484131: kvm_entry: vcpu 0 qemu-system-x86-20240 [006] d..2 9406.484132: kvm_entry: vcpu 1 qemu-system-x86-20240 [006] d..2 9406.484133: kvm_exit: reason PF excp rip 0xffffffff8161130f info 2 7fffb62ba318 We're pagefaulting on a user address 7fffb62ba318 at guest rip 0xffffffff8161130f which is: ffffffff816112da: 00 00 ffffffff816112dc: 4c 8b b3 80 03 00 00 mov 0x380(%rbx),%r14 ffffffff816112e3: 4d 39 b5 80 03 00 00 cmp %r14,0x380(%r13) ffffffff816112ea: 0f 85 38 06 00 00 jne ffffffff81611928 <__schedule+0x8a8> ffffffff816112f0: 49 83 bf 88 02 00 00 cmpq $0x0,0x288(%r15) ffffffff816112f7: 00 ffffffff816112f8: 0f 84 9a 03 00 00 je ffffffff81611698 <__schedule+0x618> ffffffff816112fe: 49 8d 7c 24 18 lea 0x18(%r12),%rdi ffffffff81611303: 48 c7 c2 fe 12 61 81 mov $0xffffffff816112fe,%rdx ffffffff8161130a: be 01 00 00 00 mov $0x1,%esi ffffffff8161130f: e8 4c 4b a9 ff callq ffffffff810a5e60 <--- ffffffff81611314: 48 8b 74 24 18 mov 0x18(%rsp),%rsi ffffffff81611319: 4c 89 ff mov %r15,%rdi ffffffff8161131c: 9c pushfq ffffffff8161131d: 55 push %rbp which, if I'm not mistaken is this here in context_switch(): #ifndef __ARCH_WANT_UNLOCKED_CTXSW spin_release(&rq->lock.dep_map, 1, _THIS_IP_); #endif Related annotated asm: #APP # 54 "/w/kernel/linux-2.6/arch/x86/include/asm/special_insns.h" 1 mov %rax,%cr3 # D.62668 # 0 "" 2 # 117 "/w/kernel/linux-2.6/arch/x86/include/asm/bitops.h" 1 .pushsection .smp_locks,"a" .balign 4 .long 671f - . .popsection 671: lock; btr %r14,888(%r13) # D.62671, MEM[(volatile long int *)_215] # 0 "" 2 #NO_APP movq 896(%rbx), %r14 # mm_193->context.ldt, D.62674 cmpq %r14, 896(%r13) # D.62674, oldmm_194->context.ldt jne .L2019 #, .L1925: cmpq $0, 648(%r15) #, prev_21->mm <--- that's the "if (!prev->mm)" test je .L2020 #, .L1931: leaq 24(%r12), %rdi #, D.62691 movq $.L1931, %rdx #, movl $1, %esi #, call lock_release # <---- the call to spin_release movq 24(%rsp), %rsi # %sfp, D.62679 movq %r15, %rdi # prev, prev #APP # 2307 "kernel/sched/core.c" 1 so it basically is the same as what we saw before. qemu-system-x86-20240 [006] ...1 9406.484134: kvm_page_fault: address 7fffb62ba318 error_code 2 qemu-system-x86-20240 [006] ...1 9406.484136: kvm_inj_exception: #PF (0x2)a kvm injects the #PF into the guest. qemu-system-x86-20240 [006] d..2 9406.484136: kvm_entry: vcpu 1 qemu-system-x86-20240 [006] d..2 9406.484137: kvm_exit: reason PF excp rip 0xffffffff8161130f info 2 7fffb62ba318 qemu-system-x86-20240 [006] ...1 9406.484138: kvm_page_fault: address 7fffb62ba318 error_code 2 qemu-system-x86-20240 [006] ...1 9406.484141: kvm_inj_exception: #DF (0x0) Second #PF at the same address and kvm injects the #DF. BUT(!), why? I probably am missing something but WTH are we pagefaulting at a user address in context_switch() while doing a lockdep call, i.e. spin_release? We're not touching any userspace gunk there AFAICT. Is this an async pagefault or so which kvm is doing so that the guest rip is actually pointing at the wrong place? Or something else I'm missing, most probably... In any case I'll try to repro with the latest kernel in the guest too. Here's the splat shown in the guest: [ 3.130253] random: nonblocking pool is initialized [ 3.700333] PANIC: double fault, error_code: 0x0 [ 3.704212] CPU: 1 PID: 911 Comm: vmmouse_detect Not tainted 3.15.0+ #1 [ 3.704212] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014 [ 3.704212] task: ffff88007b4e4dc0 ti: ffff88007aa08000 task.ti: ffff88007aa08000 [ 3.704212] RIP: 0010:[] [] __schedule+0x28f/0xab0 [ 3.704212] RSP: 002b:00007fffb62ba320 EFLAGS: 00013082 [ 3.704212] RAX: 000000007b75b000 RBX: ffff88007b5b8980 RCX: 0000000000000028 [ 3.704212] RDX: ffffffff816112fe RSI: 0000000000000001 RDI: ffff88007c5d3c58 [ 3.704212] RBP: 00007fffb62ba410 R08: ffff88007bdd3ac9 R09: 0000000000000000 [ 3.704212] R10: 0000000000000001 R11: 0000000000000019 R12: ffff88007c5d3c40 [ 3.704212] R13: ffff88007b5bb440 R14: 0000000000000000 R15: ffff88007b4e4dc0 [ 3.704212] FS: 00007fa1eec0f700(0000) GS:ffff88007c400000(0000) knlGS:0000000000000000 [ 3.704212] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 3.704212] CR2: 00007fffb62ba318 CR3: 000000007b75b000 CR4: 00000000000006e0 [ 3.704212] Stack: [ 3.704212] BUG: unable to handle kernel paging request at 00007fffb62ba320 [ 3.704212] IP: [] show_stack_log_lvl+0x11c/0x1d0 [ 3.704212] PGD 7b3ab067 PUD 0 [ 3.704212] Oops: 0000 [#1] PREEMPT SMP [ 3.704212] Modules linked in: [ 3.704212] CPU: 1 PID: 911 Comm: vmmouse_detect Not tainted 3.15.0+ #1 [ 3.704212] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014 [ 3.704212] task: ffff88007b4e4dc0 ti: ffff88007aa08000 task.ti: ffff88007aa08000 [ 3.704212] RIP: 0010:[] [] show_stack_log_lvl+0x11c/0x1d0 [ 3.704212] RSP: 002b:ffff88007c405e58 EFLAGS: 00013046 [ 3.704212] RAX: 00007fffb62ba328 RBX: 0000000000000000 RCX: ffff88007c403fc0 [ 3.704212] RDX: 00007fffb62ba320 RSI: ffff88007c400000 RDI: ffffffff81846aba [ 3.704212] RBP: ffff88007c405ea8 R08: ffff88007c3fffc0 R09: 0000000000000000 [ 3.704212] R10: 000000007c400000 R11: 0000000000000000 R12: ffff88007c405f58 [ 3.704212] R13: 0000000000000000 R14: ffffffff818136fc R15: 0000000000000000 [ 3.704212] FS: 00007fa1eec0f700(0000) GS:ffff88007c400000(0000) knlGS:0000000000000000 [ 3.704212] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 3.704212] CR2: 00007fffb62ba320 CR3: 000000007b75b000 CR4: 00000000000006e0 [ 3.704212] Stack: [ 3.704212] 0000000000000008 ffff88007c405eb8 ffff88007c405e70 000000007b75b000 [ 3.704212] 00007fffb62ba320 ffff88007c405f58 00007fffb62ba320 0000000000000040 [ 3.704212] 0000000000000ac0 ffff88007b4e4dc0 ffff88007c405f08 ffffffff81005d10 [ 3.704212] Call Trace: [ 3.704212] <#DF> [ 3.704212] [] show_regs+0xa0/0x280 [ 3.704212] [] df_debug+0x23/0x40 [ 3.704212] [] do_double_fault+0x5d/0x80 [ 3.704212] [] double_fault+0x27/0x30 [ 3.704212] [] ? __schedule+0x27e/0xab0 [ 3.704212] [] ? __schedule+0x28f/0xab0 [ 3.704212] <> [ 3.704212] Code: 7a ff ff ff 0f 1f 00 e8 93 80 00 00 eb a5 48 39 ca 0f 84 8d 00 00 00 45 85 ff 0f 1f 44 00 00 74 06 41 f6 c7 03 74 55 48 8d 42 08 <48> 8b 32 48 c7 c7 f4 36 81 81 4c 89 45 b8 48 89 4d c0 41 ff c7 [ 3.704212] RIP [] show_stack_log_lvl+0x11c/0x1d0 [ 3.704212] RSP [ 3.704212] CR2: 00007fffb62ba320 [ 3.704212] ---[ end trace 85735a6f8b08ee31 ]--- [ 3.704212] note: vmmouse_detect[911] exited with preempt_count 3 -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --