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Diffstat (limited to 'results/classifier/deepseek-2/output/hypervisor/1155')
| -rw-r--r-- | results/classifier/deepseek-2/output/hypervisor/1155 | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/results/classifier/deepseek-2/output/hypervisor/1155 b/results/classifier/deepseek-2/output/hypervisor/1155 new file mode 100644 index 00000000..13a784d5 --- /dev/null +++ b/results/classifier/deepseek-2/output/hypervisor/1155 @@ -0,0 +1,28 @@ + +RISC-V: Instruction fetch exceptions can have invalid tval/epc combination +Description of problem: +Instruction page fault / guest-page fault / access fault exceptions can have invalid `epc`/`tval` combinations, for example as shown in the debug log: + +``` +riscv_cpu_do_interrupt: hart:0, async:0, cause:0000000000000014, epc:0xffffffff802fec76, tval:0xffffffff802ff000, desc=guest_exec_page_fault +riscv_cpu_do_interrupt: hart:0, async:0, cause:0000000000000014, epc:0xffffffff80243fe6, tval:0xffffffff80244000, desc=guest_exec_page_fault +``` + +From the privileged spec: + +> If `mtval` is written with a nonzero value when an instruction access-fault or page-fault exception occurs on a system with variable-length instructions, then `mtval` will contain the virtual address of the portion of the instruction that caused the fault, while `mepc` will point to the beginning of the instruction. + +Currently RISC-V only has 32-bit and 16-bit instructions, so the difference `tval - epc` should be either `0` or `2`. In the examples above the differences are `906` and `26` respectively. + +Possibly notable: all occurrences of these invalid combinations to have `tval` aligned to a page-boundary. +Steps to reproduce: +This one only gives invalid `tval`/`epc` combinations with instruction guest-page faults, but I've found it to be the easiest reproducer to describe, since presumably running KVM in RISC-V QEMU is a standard setup. I have not otherwise been able to find a more minimal case. + +1. Start a QEMU-based `riscv64` machine +2. Start a KVM-based virtual machine with QEMU inside it +3. Do some stuff in the KVM-based virtual machine to increase the chance of page faults +4. Look in the debug log of the outer QEMU for `guest_exec_page_fault` exceptions with `tval` ending in `000`, but `epc` ending in neither `000` nor `ffe` + +Everything in both layers of guests should otherwise work without issue, but other/future software that relies on the spec-mandated relationship of `epc`/`tval` may break. +Additional information: + |