Hi Greg, Thanks, sorry for that, I'll sign them and send a new version. Alex On 3/15/2023 10:01 AM, Greg Kroah-Hartman wrote: > On Tue, Mar 14, 2023 at 11:19:51AM +0200, Alexandru Matei wrote: >> From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> >> >> commit 250552b925ce400c17d166422fde9bb215958481 upstream. >> >> When KVM runs as a nested hypervisor on top of Hyper-V it uses Enlightened >> VMCS and enables Enlightened MSR Bitmap feature for its L1s and L2s (which >> are actually L2s and L3s from Hyper-V's perspective). When MSR bitmap is >> updated, KVM has to reset HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP from >> clean fields to make Hyper-V aware of the change. For KVM's L1s, this is >> done in vmx_disable_intercept_for_msr()/vmx_enable_intercept_for_msr(). >> MSR bitmap for L2 is build in nested_vmx_prepare_msr_bitmap() by blending >> MSR bitmap for L1 and L1's idea of MSR bitmap for L2. KVM, however, doesn't >> check if the resulting bitmap is different and never cleans >> HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP in eVMCS02. This is incorrect and >> may result in Hyper-V missing the update. >> >> The issue could've been solved by calling evmcs_touch_msr_bitmap() for >> eVMCS02 from nested_vmx_prepare_msr_bitmap() unconditionally but doing so >> would not give any performance benefits (compared to not using Enlightened >> MSR Bitmap at all). 3-level nesting is also not a very common setup >> nowadays. >> >> Don't enable 'Enlightened MSR Bitmap' feature for KVM's L2s (real L3s) for >> now. >> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> >> Message-Id: <20211129094704.326635-2-vkuznets@xxxxxxxxxx> >> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> >> --- > > You did not sign off on this backport (or any of the backports), so I > can't take them sorry. > > greg k-h
