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([2001:b07:6468:f312:63a7:c72e:ea0e:6045]) by smtp.gmail.com with ESMTPSA id j12sm3080674wrt.69.2021.06.10.05.12.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Jun 2021 05:12:10 -0700 (PDT) Subject: Re: [PATCH] KVM: x86: Ensure liveliness of nested VM-Enter fail tracepoint message To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt References: <20210607175748.674002-1-seanjc@google.com> From: Paolo Bonzini Message-ID: <1e8fda75-4c34-b13f-b193-4def6869b0f2@redhat.com> Date: Thu, 10 Jun 2021 14:12:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210607175748.674002-1-seanjc@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 07/06/21 19:57, Sean Christopherson 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 > > Cc: Steven Rostedt > Fixes: 380e0055bc7e ("KVM: nVMX: trace nested VM-Enter failures detected by H/W") > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/trace.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h > index a61c015870e3..4f839148948b 100644 > --- a/arch/x86/kvm/trace.h > +++ b/arch/x86/kvm/trace.h > @@ -1550,16 +1550,16 @@ TRACE_EVENT(kvm_nested_vmenter_failed, > TP_ARGS(msg, err), > > TP_STRUCT__entry( > - __field(const char *, msg) > + __string(msg, msg) > __field(u32, err) > ), > > TP_fast_assign( > - __entry->msg = msg; > + __assign_str(msg, msg); > __entry->err = err; > ), > > - TP_printk("%s%s", __entry->msg, !__entry->err ? "" : > + TP_printk("%s%s", __get_str(msg), !__entry->err ? "" : > __print_symbolic(__entry->err, VMX_VMENTER_INSTRUCTION_ERRORS)) > ); > > Queued, thanks. Paolo