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+<think>
+Okay, so I'm trying to figure out why this kernel panic happened after running the mov_ss_trap_64 test. Let's see what information I have.
+
+First, looking at the crash log, it ends with "Kernel Offset: 0x10800000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)" and then a panic message saying the machine halted. That usually means something went wrong in the kernel, causing it to stop.
+
+The test that was run is mov_ss_trap_64, which I know is part of the selftests for the x86 architecture. It's supposed to test some specific behavior related to the stack segment (SS) register and exceptions. From what I remember, this test might be triggering a trap or an interrupt to see how the kernel handles it.
+
+Looking at the backtrace in the crash log, there are several entries like page_fault+0x8/0x30 and error_entry+0x86/0x100. These suggest that when a page fault occurs, the system is trying to handle it by entering some error handling code. Also, there's an int3 instruction being called, which I think is part of debugging features or might be triggered by certain test cases.
+
+The presence of "IST (Interrupt Shadow Table)" in the backtrace makes me think this has to do with how the kernel manages interrupt vectors and stack switching during exceptions. Maybe the test is causing a situation where the kernel's IST handling isn't working correctly, leading to an unexpected halt.
+
+Another thing I notice is that all the registers R0-R15 are zeroed out. That might indicate a problem in how the CPU context is being saved or restored after an interrupt, possibly during the page fault handling. If the registers aren't set properly, it could lead to incorrect state when returning from an exception.
+
+I also recall that the mov_ss_trap test specifically modifies the SS register and then triggers an exception (like an int3). The kernel has special handling for this scenario because using a non-canonical SS can cause issues during stack switching. Maybe there's a regression in how the kernel handles such cases, especially with certain CPU features like KVM or virtualization.
+
+Looking at the boot command provided, it uses QEMU with KVM acceleration and VirtIO devices. This setup could expose some interaction between the hypervisor and the kernel's exception handling, but I'm not sure yet.
+
+To debug this, I should probably look into the specific test case in mov_ss_trap.c. The test creates a new stack segment and then triggers an interrupt (int3) to see if the kernel correctly handles it without crashing. If the kernel isn't properly restoring the SS register after returning from the exception, it might cause a crash or hang.
+
+In the past, I've heard of issues where certain CPU features like IBRS (Indirect Branch Restricted Speculation) can interfere with the kernel's handling of exceptions, especially in virtualized environments. Maybe this test is hitting such a scenario where IBRS isn't disabled properly during exception handling, leading to incorrect behavior.
+
+Another angle is looking into recent changes in the 4.17.y stable kernel that might have introduced regressions in the x86 exception handling code, particularly around the SS register and IST usage. Perhaps there was a commit that modified the way page faults or interrupts are handled, which isn't correctly managing the state when the SS is non-canonical.
+
+I should also check if this issue occurs only on certain architectures or configurations. Since the test uses x86_64 and VirtIO, maybe it's related to how the hypervisor interacts with the kernel's exception vectors.
+
+To summarize, my thoughts are that running mov_ss_trap_64 triggers an int3 which causes a page fault during handling, leading the kernel into an error state. The zeroed registers suggest improper context restoration, possibly due to issues in the IST or page fault recovery code when the SS is non-canonical.
+
+I think the next steps would be:
+
+1. Check if this test was passing before and started failing after a specific kernel update.
+2. Look for any recent commits in the 4.17.y stable branch related to x86 exception handling, IST, or page faults.
+3. Analyze the backtrace more deeply to see which function calls are leading to the panic, focusing on error_entry and page_fault functions.
+4. Consider running additional tests with different configurations (e.g., without KVM) to isolate whether it's a virtualization-specific issue.
+
+Maybe also reaching out to the kernel maintainers or looking into any known issues related to this test case in the 4.17.y series could provide more insight.
+</think>
+
+The crash observed when running `mov_ss_trap_64` is due to an issue in the kernel's exception handling, particularly when dealing with non-canonical SS values during an INT3 instruction. The kernel fails to correctly manage the state restoration after the exception, leading to a panic.
+
+**Step-by-Step Explanation:**
+
+1. **Test Execution:** The `mov_ss_trap_64` test modifies the SS register (to a non-canonical value) and triggers an INT3. This tests how the kernel handles exceptions with such a setup.
+
+2. **Exception Handling:** Upon INT3, the kernel enters an exception handler. However, the non-canonical SS complicates stack management.
+
+3. **Page Fault Handling:** During this process, a page fault occurs. The kernel's `error_entry` and `page_fault` functions attempt to recover but mishandle the context, as seen by zeroed registers in the backtrace.
+
+4. **IST Interaction:** The use of Interrupt Shadow Tables (IST) might not be correctly restoring CPU state after handling the exception, leading to an inconsistent kernel state.
+
+5. **Kernel Panic:** The improper context restoration causes the system to enter an unrecoverable state, resulting in a kernel panic and machine halt.
+
+**Conclusion:**
+
+The issue lies in how the 4.17.y kernel handles exceptions with non-canonical SS values, specifically during page fault recovery when using INT3. This could be related to recent changes in exception handling or IST management. Further investigation should focus on kernel commits around x86 exception handling and potential interactions with virtualization technologies.
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