On 28/11/16 19:42, Christoffer Dall wrote: > On Mon, Nov 28, 2016 at 06:39:04PM +0000, Marc Zyngier wrote: >> On 28/11/16 17:43, Marc Zyngier wrote: >>> Hi Jintack, >>> >>> On 28/11/16 16:46, Jintack Lim wrote: >>>> Bit positions of CNTHCTL_EL2 are changing depending on HCR_EL2.E2H bit. >>>> EL1PCEN and EL1PCTEN are 1st and 0th bits when E2H is not set, but they >>>> are 11th and 10th bits respectively when E2H is set. Current code is >>>> unintentionally setting wrong bits to CNTHCTL_EL2 with E2H set, which >>>> may allow guest OS to access physical timer. So, fix it. >>>> >>>> Signed-off-by: Jintack Lim <jintack@xxxxxxxxxxxxxxx> >>>> --- >>>> arch/arm/include/asm/kvm_timer.h | 33 +++++++++++++++++++ >>>> arch/arm64/include/asm/kvm_timer.h | 62 ++++++++++++++++++++++++++++++++++++ >>>> include/clocksource/arm_arch_timer.h | 6 ++-- >>>> virt/kvm/arm/hyp/timer-sr.c | 8 ++--- >>>> 4 files changed, 103 insertions(+), 6 deletions(-) >>>> create mode 100644 arch/arm/include/asm/kvm_timer.h >>>> create mode 100644 arch/arm64/include/asm/kvm_timer.h >>>> >> >> [...] >> >>> We could make it nicer (read "faster") by introducing a >>> hyp_alternate_select construct that only returns a value instead >>> of calling a function. I remember writing something like that >>> at some point, and dropping it... >> >> So here's what this could look like (warning, wacky code ahead, >> though I fixed a stupid bug that was present in the previous patch). >> The generated code is quite nice (no branch, only an extra mov >> instruction on the default path)... Of course, completely untested! > > Isn't this all about determining which bitmask to use, statically, once, > after the system has booted? > > How about a good old fashioned static variable, or global struct like > the global one we use for the VGIC, which sets the proper mit mask > during kvm init, and the world-switch code just uses a variable? We could indeed do that (I've been carried away with my tendency for weird and wonderful hacks). But as Jintack mentioned, there is a much better approach, which is to do nothing at all on the VHE path (we can set the permission bits once and for all). cntvoff_el2 also falls into the same category of things we should be able to only restore and not bother resetting (as it doesn't affect the EL2 virtual counter). Thoughts? M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
