2017-08-10 6:02 GMT+08:00 Anatol Pomozov <anatol.pomozov@xxxxxxxxx>: > Hello Wanpeng > > Unfortunately I do not have a simple test case for this issue. The > issue I see is with a large non-published project compiled with the > latest version of clang. > > Isn't information provided by QEMU enough? Is there a way to enable > additional debug log in KVM? KVM just has basic support to SSE emulation, and it can't emulate the movups instruction currently, in addition, I can reproduce this by a small change in kvm-unit-tests/emulator.flat. Regards, Wanpeng Li > > On Mon, Aug 7, 2017 at 3:00 PM, Wanpeng Li <kernellwp@xxxxxxxxx> wrote: >> 2017-08-08 2:45 GMT+08:00 Anatol Pomozov <anatol.pomozov@xxxxxxxxx>: >>> 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. >> >> Actually the KVM supports SSE emulation in some degree, please post >> your testcase here. >> >> Regards, >> Wanpeng Li
