On Mon, 2022-03-28 at 19:12 +0200, Paolo Bonzini wrote: > On 3/27/22 17:12, Maxim Levitsky wrote: > > - with LBR virtualization supported, the guest can set this msr to any value > > as long as it doesn't set reserved bits and then read back the written value, > > but it is not used by the CPU, unless LBR bit is set in MSR_IA32_DEBUGCTLMSR, > > because only then LBR virtualization is enabled, which makes the CPU > > load the guest value on VM entry. > > > > This means that MSR_IA32_DEBUGCTLMSR.BTF will magically start working when > > MSR_IA32_DEBUGCTLMSR.LBR is set as well, and will not work otherwise. > > That can be fixed by context-switching DEBUGCTLMSR by hand when LBR=0 && > BTF=1. Would you like to give it a shot? > > Paolo > Yep exactly, I didn't do that yet only because mypatches didn't made it worse, so I wanted to do this in a separate patch (+unit test), and it kind of went to my backlog. I'll do that soon. Best regards, Maxim Levitsky
