On Mon, Feb 06, 2023 at 06:05:44AM +0000, Manali Shukla wrote: > Add a function to set per-cpu ibs_flags based on an active or inactive > PreventHostIBS window. > > MSR_AMD64_IBSFETCHCTL[IbsFetchEn] and MSR_AMD64_IBSOPCTL[IbsOpEn] bits > need to be cleared for PreventHostIBS feature to be enabled before VMRUN > is executed. > > ENABLE bit and VALID bit for MSR_AMD64_IBSFETCHCTL are contained in the > same MSR and same is the case with MSR_AMD64_IBSOPCTL. > > Consider the following scenario: > - The IBS MSR which has ENABLE bit set and VALID bit clear is read. > - During the process of clearing the ENABLE bit and writing the IBS MSR > to disable IBS, an IBS event can occur that sets the VALID bit. > - The write operation on IBS MSR can clear the newly set VALID bit. > - Since this situation is occurring in the CLGI/STGI window > (PreventHostIBS window), the actual NMI is not taken. > - Once VMRUN is issued, it will exit with VMEXIT_NMI. As soon as STGI is > executed, the pending NMI will trigger. > - The IBS NMI handler checks for the VALID bit to determine if the NMI > is generated because of IBS. > - Since VALID bit is now clear, it doesn't recognize that an IBS event > is occurred. Due to this reason, the dazed and confused unknown NMI > messages are generated. > > amd_prevent_hostibs_window() is added to avoid these messages when > PreventHostIBS window is active and PreventHostIBS feature is enabled > for the guest. > > Signed-off-by: Manali Shukla <manali.shukla@xxxxxxx> URGH... so am I reading this right that this is a sodding terrible software implementation of perf_event_attr::exclude_guest ?
