Hi David On Mon, Aug 7, 2017 at 9:59 AM, David Matlack <dmatlack@xxxxxxxxxx> wrote: > Likely this instruction is accessing an MMIO region (probably a VGA > buffer, given "mov $0xb8f0e,%ecx"). This will cause a trap to KVM > and KVM will try to emulate the instruction. The instruction doing the > MMIO access is an SSE instruction, It is correct. The emulation error happens in printf() kernel function that formats a string and then prints it VGA area. Compilers (both clang and gcc) think that SSE instructions are more efficient in dealing with strings and that's why I have SSE instructions here. > which KVM does not have support to > emulate, thus the internal error. If you didn't hand write this > assembly I would try compiling your kernel with compilation flags to > disable SSE code generation and see if that fixes your issue. Adding "-mno-sse" and removing some floating point functionality in my kernel make the emulation error go away. So it confirms your thesis. Though I need floating point/SSE in my kernel and I can't disable SSE completely. Instead I would love to understand why KVM can't use SSE with VGA memory? I tested my kernel binary with bare hardware, KVM, VMWare, QEMU and only KVM fails.
