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SubjectRe: [PATCH v2] x86/fault: Decode and print #PF oops in human readable form
On Fri, Dec 07, 2018 at 12:46:30PM -0800, Linus Torvalds wrote:
> On Fri, Dec 7, 2018 at 11:52 AM Sean Christopherson
> <sean.j.christopherson@intel.com> wrote:
> >
> > Remove the per-bit decoding of the error code and instead print:
>
> The patch looks fine to me, so feel free to add an acked-by, but:
>
> (a) I'm not the one who wanted the human-legible version in the first
> place, since I'm also perfectly ok with just the error code, so my
> judgement is obviously garbage wrt this whole thing
>
> (b) it would be good to have a couple of actual examples of the
> printout to judge.
>
> I can certainly imagine how it looks just from the patch, but maybe if
> I actually see reality I'd go "eww". Or somebody else goes "eww".

Here's what it looks like in the full oops context:

[ 14.109977] BUG: unable to handle kernel paging request at ffffbeef00000000
[ 14.110604] #PF: error_code(0x0000) - not-present page
[ 14.111048] #PF: supervisor-privileged read access from kernel code
[ 14.111594] PGD 0 P4D 0
[ 14.111820] Oops: 0000 [#1] SMP
[ 14.112098] CPU: 4 PID: 1007 Comm: modprobe Not tainted 4.20.0-rc2+ #91
[ 14.112668] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
[ 14.113344] RIP: 0010:hardware_setup+0xab/0x6f1 [kvm_intel]
[ 14.113825] Code: 05 30 8c ff ff 0f 84 56 05 00 00 0f 31 83 e0 03 75 13 48 b8 00 00 00 00 ef be ff ff 48 c7 00 00 00 00 00 eb 2b 48 ff c8 75 0c <48> a1 00 00 00 00 ef be ff ff eb 1a 48 8b 15 50 ff f6 ff 48 b8 00
[ 14.115421] RSP: 0018:ffffc9000058bbb8 EFLAGS: 00010246
[ 14.115878] RAX: 0000000000000000 RBX: 0000000000000006 RCX: ffffea0009d42148
[ 14.116497] RDX: 000000000000000a RSI: dead000000000200 RDI: 00000000006000c0
[ 14.117115] RBP: ffffc9000058bc50 R08: 0000000000000006 R09: 000000000016a6d0
[ 14.117731] R10: ffffc9000058bc68 R11: ffff8882750ef5e8 R12: 0000000000005e40
[ 14.118346] R13: ffffffffa014dd00 R14: ffff888270273480 R15: ffffc9000058be98
[ 14.118961] FS: 00007ffac1c70700(0000) GS:ffff888277800000(0000) knlGS:0000000000000000
[ 14.119661] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 14.120160] CR2: ffffbeef00000000 CR3: 0000000270352004 CR4: 0000000000360ee0
[ 14.120778] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 14.121393] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 14.122006] Call Trace:
[ 14.122235] kvm_arch_hardware_setup+0x42/0x200 [kvm]
[ 14.122685] ? vmx_check_processor_compat+0x8d/0x8d [kvm_intel]
[ 14.123201] ? kvm_init+0x79/0x280 [kvm]
[ 14.123552] kvm_init+0x79/0x280 [kvm]
[ 14.123883] ? vmx_check_processor_compat+0x8d/0x8d [kvm_intel]
[ 14.124394] vmx_init+0x9d/0x400 [kvm_intel]
[ 14.124766] ? vmx_check_processor_compat+0x8d/0x8d [kvm_intel]
[ 14.125277] do_one_initcall+0x4d/0x1c4
[ 14.125613] ? kmem_cache_alloc_trace+0x30/0x1a0
[ 14.126014] do_init_module+0x5b/0x20d
[ 14.126342] load_module+0x2389/0x2980
[ 14.126670] ? vfs_read+0x117/0x130
[ 14.126976] ? __do_sys_finit_module+0xd2/0x100
[ 14.127369] __do_sys_finit_module+0xd2/0x100
[ 14.127751] do_syscall_64+0x4f/0x100
[ 14.128078] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 14.128504] RIP: 0033:0x7ffac178e4d9
[ 14.128810] Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 8f 29 2c 00 f7 d8 64 89 01 48
[ 14.130358] RSP: 002b:00007ffc5b68d0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
[ 14.131023] RAX: ffffffffffffffda RBX: 00005581920445c0 RCX: 00007ffac178e4d9
[ 14.131658] RDX: 0000000000000000 RSI: 0000558192048850 RDI: 0000000000000005
[ 14.132256] RBP: 0000558192048850 R08: 0000000000000000 R09: 0000000000000008
[ 14.132856] R10: 0000000000000005 R11: 0000000000000246 R12: 0000000000000000
[ 14.133454] R13: 0000558192044640 R14: 0000000000040000 R15: 0000000000000008
[ 14.134055] Modules linked in: kvm_intel(+) kvm irqbypass bridge stp llc
[ 14.134649] CR2: ffffbeef00000000
[ 14.134933] ---[ end trace 8dce06ca17fa1e39 ]---


Looking at it again, my own personal preference would be to swap the order
of the #PF lines. For most cases the three main lines show up in reverse
fir-tree ordering and the cause of the fault is easy to pick out since it's
the last thing highlighted by pr_alert (excepting when we dump the IDT,
GDT, etc...).

[ 160.246820] BUG: unable to handle kernel paging request at ffffbeef00000000
[ 160.247517] #PF: supervisor-privileged instruction fetch from kernel code
[ 160.248085] #PF: error_code(0x0010) - not-present page
[ 160.248517] PGD 0 P4D 0
[ 160.248738] Oops: 0010 [#1] SMP
[ 160.249012] CPU: 4 PID: 1003 Comm: modprobe Not tainted 4.20.0-rc2+ #93
[ 160.249566] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
[ 160.250221] RIP: 0010:0xffffbeef00000000
[ 160.250556] Code: Bad RIP value.
[ 160.250833] RSP: 0018:ffffc90000447bf8 EFLAGS: 00010246
[ 160.251274] RAX: ffffbeef00000000 RBX: 00000000ffffffff RCX: 0000000000000000
[ 160.251871] RDX: ffff8882733dd7c0 RSI: 000000000000000c RDI: ffffffff820379c0
[ 160.252469] RBP: ffffc90000447c50 R08: 0000000000000006 R09: 0000000000000000
[ 160.253120] R10: ffffc90000447c68 R11: ffff88827518cfe8 R12: 0000000000005e40
[ 160.253717] R13: ffffffffa014dd00 R14: ffff888274431900 R15: ffffc90000447e98
[ 160.254322] FS: 00007f54cc42b700(0000) GS:ffff888277800000(0000) knlGS:0000000000000000
[ 160.254982] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 160.255487] CR2: ffffbeeeffffffd6 CR3: 0000000271020006 CR4: 0000000000360ee0
[ 160.256074] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 160.256660] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 160.257297] Call Trace:
[ 160.257521] ? kvm_arch_hardware_setup+0x42/0x200 [kvm]
[ 160.257964] ? vmx_check_processor_compat+0x41d/0x41d [kvm_intel]
[ 160.258481] ? kvm_init+0x79/0x280 [kvm]
[ 160.258820] ? kvm_init+0x79/0x280 [kvm]
[ 160.259156] ? vmx_check_processor_compat+0x41d/0x41d [kvm_intel]
[ 160.259669] ? vmx_init+0x9d/0xaee [kvm_intel]
[ 160.260047] ? vmx_check_processor_compat+0x41d/0x41d [kvm_intel]
[ 160.260560] ? do_one_initcall+0x4d/0x1c4
[ 160.260911] ? kmem_cache_alloc_trace+0x30/0x1a0
[ 160.261307] ? do_init_module+0x5b/0x20d
[ 160.261641] ? load_module+0x2389/0x2980
[ 160.261974] ? vfs_read+0x117/0x130
[ 160.262272] ? __do_sys_finit_module+0xd2/0x100
[ 160.262655] ? __do_sys_finit_module+0xd2/0x100
[ 160.263038] ? do_syscall_64+0x4f/0x100
[ 160.263364] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 160.263804] Modules linked in: kvm_intel(+) kvm irqbypass bridge stp llc
[ 160.264367] CR2: ffffbeef00000000
[ 160.264651] ---[ end trace 2b9acada0f38bc58 ]---


Other combinations with the current order:

[ 0.143436] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.143985] #PF: error_code(0x000b) - reserved bit violation
[ 0.144505] #PF: supervisor-privileged write access from kernel code

[ 0.145090] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.145755] #PF: error_code(0x0019) - reserved bit violation
[ 0.146244] #PF: supervisor-privileged instruction fetch from kernel code

[ 0.146847] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0009) - reserved bit violation
[ 0.147040] #PF: supervisor-privileged read access from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0023) - protection keys violation
[ 0.147040] #PF: supervisor-privileged write access from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0031) - protection keys violation
[ 0.147040] #PF: supervisor-privileged instruction fetch from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0021) - protection keys violation
[ 0.147040] #PF: supervisor-privileged read access from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0025) - protection keys violation
[ 0.147040] #PF: user-privileged read access from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0007) - permissions violation
[ 0.147040] #PF: user-privileged write access from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0015) - permissions violation
[ 0.147040] #PF: user-privileged instruction fetch from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0005) - permissions violation
[ 0.147040] #PF: user-privileged read access from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0004) - not-present page
[ 0.147040] #PF: user-privileged read access from kernel code

[ 0.147040] BUG: unable to handle kernel paging request at ffffc90000230000
[ 0.147040] #PF: error_code(0x0000) - not-present page
[ 0.147040] #PF: supervisor-privileged read access from kernel code

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