https://bugzilla.kernel.org/show_bug.cgi?id=201249 Bug ID: 201249 Summary: Emulation of compatibility mode 32-bit SYSCALL fails with TF flag set on Intel hosts Product: Virtualization Version: unspecified Kernel Version: 4.4.0-21-generic or 4.18.9-gentoo Hardware: Intel OS: Linux Tree: Mainline Status: NEW Severity: low Priority: P1 Component: kvm Assignee: virtualization_kvm@xxxxxxxxxxxxxxxxxxxx Reporter: r.marek@xxxxxxxxxxxx Regression: No Created attachment 278781 --> https://bugzilla.kernel.org/attachment.cgi?id=278781&action=edit Reproducer for this issue The emulation of 32-bit SYSCALL instruction while running in compatibility mode on Intel hosts breaks if TF flag is set while executing the 32-bit SYSCALL instruction. The instruction will be never executed and one would get single step exception again and again. The attached reproducer2.c manifests the issue if some 64-bit Linux is run inside the QEMU with KVM and gdb is used to singlestep through a 32-bit executable until it gets again and again stuck on SYSCALL instruction. Steps to reproduce: 1) compile with gcc -m32 reproducer2.c -o reproducer2 (or alternatively compile it inside the guest) 2) run kvm + qemu and some Linux distro with a directory kvm-bug which contains the executable, thehost KVM needs to run on Intel CPU! qemu-system-x86_64 -enable-kvm -m 2048 -cdrom /tmp/ubuntu-18.04.1-desktop-amd64.iso -boot d -drive file=fat:rw:kvm-bug Wait until it boots, mount the virtual drive and then invoke: 3) gdb ./reproducer2 4) break on main and then "stepi" until SYSCALL is reached, stepi is going to be stuck on SYSCALL and never executing it. Singlestepping in gdb through reproducer2 works on real AMD system just fine. -- You are receiving this mail because: You are watching the assignee of the bug.
