On 19/12/19 21:32, Sean Christopherson wrote: > On Thu, Dec 19, 2019 at 02:17:59PM -0600, John Allen wrote: >> Current SVM implementation does not have support for handling PKU. Guests >> running on a host with future AMD cpus that support the feature will read >> garbage from the PKRU register and will hit segmentation faults on boot as >> memory is getting marked as protected that should not be. Ensure that cpuid >> from SVM does not advertise the feature. >> >> Signed-off-by: John Allen <john.allen@xxxxxxx> >> --- >> v2: >> -Introduce kvm_x86_ops->pku_supported() > > I like the v1 approach better, it's less code to unwind when SVM gains > support for virtualizaing PKU. > > The existing cases of kvm_x86_ops->*_supported() in __do_cpuid_func() are > necessary to handle cases where it may not be possible to expose a feature > even though it's supported in hardware, host and KVM, e.g. VMX's separate > MSR-based features and PT's software control to hide it from guest. In > this case, hiding PKU is purely due to lack of support in KVM. The SVM > series to enable PKU can then delete a single line of SVM code instead of > having to go back in and do surgery on x86 and VMX. > I sort of liked the V1 approach better, in that I liked using set_supported_cpuid but I didn't like *removing* features from it. I think all *_supported() should be removed, and the code moved from __do_cpuid_func() to set_supported_cpuid. For now, however, this one is consistent with other features so I am applying it. Paolo
