On Wed, Jun 09, 2021, Wanpeng Li wrote: > On Tue, 8 Jun 2021 at 02:00, Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > > > Use the __string() machinery provided by the tracing subystem to make a > > copy of the string literals consumed by the "nested VM-Enter failed" > > tracepoint. A complete copy is necessary to ensure that the tracepoint > > can't outlive the data/memory it consumes and deference stale memory. > > > > Because the tracepoint itself is defined by kvm, if kvm-intel and/or > > kvm-amd are built as modules, the memory holding the string literals > > defined by the vendor modules will be freed when the module is unloaded, > > whereas the tracepoint and its data in the ring buffer will live until > > kvm is unloaded (or "indefinitely" if kvm is built-in). > > > > This bug has existed since the tracepoint was added, but was recently > > exposed by a new check in tracing to detect exactly this type of bug. > > > > fmt: '%s%s > > ' current_buffer: ' vmx_dirty_log_t-140127 [003] .... kvm_nested_vmenter_failed: ' > > WARNING: CPU: 3 PID: 140134 at kernel/trace/trace.c:3759 trace_check_vprintf+0x3be/0x3e0 > > CPU: 3 PID: 140134 Comm: less Not tainted 5.13.0-rc1-ce2e73ce600a-req #184 > > Hardware name: ASUS Q87M-E/Q87M-E, BIOS 1102 03/03/2014 > > RIP: 0010:trace_check_vprintf+0x3be/0x3e0 > > Code: <0f> 0b 44 8b 4c 24 1c e9 a9 fe ff ff c6 44 02 ff 00 49 8b 97 b0 20 > > RSP: 0018:ffffa895cc37bcb0 EFLAGS: 00010282 > > RAX: 0000000000000000 RBX: ffffa895cc37bd08 RCX: 0000000000000027 > > RDX: 0000000000000027 RSI: 00000000ffffdfff RDI: ffff9766cfad74f8 > > RBP: ffffffffc0a041d4 R08: ffff9766cfad74f0 R09: ffffa895cc37bad8 > > R10: 0000000000000001 R11: 0000000000000001 R12: ffffffffc0a041d4 > > R13: ffffffffc0f4dba8 R14: 0000000000000000 R15: ffff976409f2c000 > > FS: 00007f92fa200740(0000) GS:ffff9766cfac0000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000559bd11b0000 CR3: 000000019fbaa002 CR4: 00000000001726e0 > > Call Trace: > > trace_event_printf+0x5e/0x80 > > trace_raw_output_kvm_nested_vmenter_failed+0x3a/0x60 [kvm] > > print_trace_line+0x1dd/0x4e0 > > s_show+0x45/0x150 > > seq_read_iter+0x2d5/0x4c0 > > seq_read+0x106/0x150 > > vfs_read+0x98/0x180 > > ksys_read+0x5f/0xe0 > > do_syscall_64+0x40/0xb0 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > I can observe tons of other kvm tracepoints warning like this after > commit 9a6944fee68e25 (tracing: Add a verifier to check string > pointers for trace events), just echo 1 > > /sys/kernel/tracing/events/kvm/enable and boot a linux guest. Can you provide your .config? With all of events/kvm and events/kvmmmu enabled I don't get any warnings running a Linux guest, a nested Linux guest, and kvm-unit-tests. Do you see the behavior with other tracepoints? E.g. enabling all events on my systems yields warnings for a USB module, but everything else is clean.
