On Wed, Nov 30, 2016 at 10:41 AM, Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: > 2016-11-29 12:40-0800, Kyle Huey: >> KVM does not currently honor the trap flag when emulating instructions that >> cause VM exits. This is observable from guest userspace, try stepping on a >> CPUID instruction in gdb in a KVM guest. The program will stop two >> instructions after CPUID. >> >> To fix this, add kvm_skip_emulated_instruction that calls >> kvm_x86_ops->skip_emulated_instruction and then kvm_vcpu_check_singlestep to >> check for RFLAGS.TF. Patch 4 does this. To handle both the guest setting TF >> and the KVM_GUESTDBG_SINGLESTEP cases we need to be able to indicate to >> callees that an exit to userspace is required. Patches 1-3 are largely >> plumbing to make this possible. >> >> Traps triggered by task switch instructions require some additional handling >> and are not implemented. KVM_GUESTDBG_SINGLESTEP traps can be squashed by >> certain instructions which also trigger userspace exits, such as HALT, >> MOV CR8, and IO instructions. I believe (although I have not tested) that >> KVM will simply generate another trap on the next instruction, so this is >> no worse than the current behavior. >> >> Patch 5 fixes an existing bug where kvm_vcpu_check_singlestep clears >> RFLAGS.TF when generating a singlestep trap. Bare silicon does not do this. > > Looks good, applied to kvm/queue. Great! Thank you. >> These patches only fix this issue for VMX, and the handful of SVM cases that >> call the shared kvm_complete_insn_gp. I don't have AMD silicon to test on. > > Added to TODO, > > Thanks. - Kyle -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
