Hi, On 2/13/19 11:04 PM, Kristina Martsenko wrote: > 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. This patch is not directly related to pointer authentication but just a helper to optimize save/restore. In this way save may be avoided for each switch and only restore is done. Patch 3 does sets HCR_EL2 in VHE_RUN. > > 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? Now HCR_EL2 is modified during switch time and NHVE doesnt support ptrauth so [2] doesn't makes sense. //Amit D > > 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/ >
