On Wed, Jun 10, 2020 at 9:41 AM Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote: > > It was reported that older GCCs compile smm_test in a way that breaks > it completely: > > kvm_exit: reason EXIT_CPUID rip 0x4014db info 0 0 > func 7ffffffd idx 830 rax 0 rbx 0 rcx 0 rdx 0, cpuid entry not found > ... > kvm_exit: reason EXIT_MSR rip 0x40abd9 info 0 0 > kvm_msr: msr_read 487 = 0x0 (#GP) > ... > > Note, '7ffffffd' was supposed to be '80000001' as we're checking for > SVM. Dropping '-O2' from compiler flags help. Turns out, asm block in > sync_with_host() is wrong. We us 'in 0xe, %%al' instruction to sync > with the host and in 'AL' register we actually pass the parameter > (stage) but after sync 'AL' gets written to but GCC thinks the value > is still there and uses it to compute 'EAX' for 'cpuid'. That smells like VMware's hypercall madness! > smm_test can't fully use standard ucall() framework as we need to > write a very simple SMI handler there. Fix the immediate issue by > making RAX input/output operand. While on it, make sync_with_host() > static inline. > > Reported-by: Marcelo Bandeira Condotta <mcondotta@xxxxxxxxxx> > Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
