On 28/01/2019 06:58, Amit Daniel Kachhap wrote: > When restoring HCR_EL2 for the host, KVM uses HCR_HOST_VHE_FLAGS, which > is a constant value. This works today, as the host HCR_EL2 value is > always the same, but this will get in the way of supporting extensions > that require HCR_EL2 bits to be set conditionally for the host. > > To allow such features to work without KVM having to explicitly handle > every possible host feature combination, this patch has KVM save/restore > the host HCR when switching to/from a guest HCR. The saving of the > register is done once during cpu hypervisor initialization state and is > just restored after switch from guest. Why is this patch needed? I couldn't find anything in this series that sets HCR_EL2 conditionally for the host. It seems like the kernel still always sets it to HCR_HOST_VHE_FLAGS/HCR_HOST_NVHE_FLAGS. Looking back at v2 of the userspace pointer auth series, it seems that the API/APK bits were set conditionally [1], so this patch would have been needed to preserve HCR_EL2. But as of v3 of that series, the bits have been set unconditionally through HCR_HOST_NVHE_FLAGS [2]. Is there something else I've missed? Thanks, Kristina [1] https://lore.kernel.org/linux-arm-kernel/20171127163806.31435-6-mark.rutland at arm.com/ [2] https://lore.kernel.org/linux-arm-kernel/20180417183735.56985-5-mark.rutland at arm.com/
