Hi, While investigating KMSAN's incompatibilities with the default Ubuntu config (https://github.com/google/kmsan/issues/89#issuecomment-1310702949), I figured out that a kernel won't boot with both CONFIG_KMSAN=y and CONFIG_XEN_PV=y. In particular, it may crash in load_percpu_segment(): __loadsegment_simple(gs, 0); wrmsrl(MSR_GS_BASE, cpu_kernelmode_gs_base(cpu)); Here the value of %gs between __loadsegment_simple() and wrmsrl() is zero, so when KMSAN's __msan_get_context_state() instrumentation function is called before the actual WRMSR instruction is performed, it will attempt to access percpu data and crash. Unless instructed otherwise (by noinstr or __no_sanitize_memory on the source level, or by KMSAN_SANITIZE := n on the Makefile level), KMSAN inserts instrumentation at function prologue for every non-inlined function, including native_write_msr(). Marking native_write_msr() noinstr actually makes the kernel boot for me, but I am not sure if this is enough. In fact we'll need to fix every situation in which instrumentation code may be called with invalid %gs value. Do you think this is feasible? Overall, should we care about KMSAN working with paravirtualization? Thank you, -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Liana Sebastian Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
