On Wed, Jul 03, 2019 at 10:21:57AM +0100, Marc Zyngier wrote: > On 24/06/2019 13:48, Dave Martin wrote: > > On Fri, Jun 21, 2019 at 02:50:08PM +0100, Marc Zyngier wrote: > >> On 21/06/2019 14:24, Julien Thierry wrote: > >>> > >>> > >>> On 21/06/2019 10:37, Marc Zyngier wrote: > >>>> From: Christoffer Dall <christoffer.dall@xxxxxxxxxx> > >>>> > >>>> We were not allowing userspace to set a more privileged mode for the VCPU > >>>> than EL1, but we should allow this when nested virtualization is enabled > >>>> for the VCPU. > >>>> > >>>> Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> > >>>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> > >>>> --- > >>>> arch/arm64/kvm/guest.c | 6 ++++++ > >>>> 1 file changed, 6 insertions(+) > >>>> > >>>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c > >>>> index 3ae2f82fca46..4c35b5d51e21 100644 > >>>> --- a/arch/arm64/kvm/guest.c > >>>> +++ b/arch/arm64/kvm/guest.c > >>>> @@ -37,6 +37,7 @@ > >>>> #include <asm/kvm_emulate.h> > >>>> #include <asm/kvm_coproc.h> > >>>> #include <asm/kvm_host.h> > >>>> +#include <asm/kvm_nested.h> > >>>> #include <asm/sigcontext.h> > >>>> > >>>> #include "trace.h" > >>>> @@ -194,6 +195,11 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg) > >>>> if (vcpu_el1_is_32bit(vcpu)) > >>>> return -EINVAL; > >>>> break; > >>>> + case PSR_MODE_EL2h: > >>>> + case PSR_MODE_EL2t: > >>>> + if (vcpu_el1_is_32bit(vcpu) || !nested_virt_in_use(vcpu)) > >>> > >>> This condition reads a bit weirdly. Why do we care about anything else > >>> than !nested_virt_in_use() ? > >>> > >>> If nested virt is not in use then obviously we return the error. > >>> > >>> If nested virt is in use then why do we care about EL1? Or should this > >>> test read as "highest_el_is_32bit" ? > >> > >> There are multiple things at play here: > >> > >> - MODE_EL2x is not a valid 32bit mode > >> - The architecture forbids nested virt with 32bit EL2 > >> > >> The code above is a simplification of these two conditions. But > >> certainly we can do a bit better, as kvm_reset_cpu() doesn't really > >> check that we don't create a vcpu with both 32bit+NV. These two bits > >> should really be exclusive. > > > > This code is safe for now because KVM_VCPU_MAX_FEATURES <= > > KVM_ARM_VCPU_NESTED_VIRT, right, i.e., nested_virt_in_use() cannot be > > true? > > > > This makes me a little uneasy, but I think that's paranoia talking: we > > want bisectably, but no sane person should ship with just half of this > > series. So I guess this is fine. > > > > We could stick something like > > > > if (WARN_ON(...)) > > return false; > > > > in nested_virt_in_use() and then remove it in the final patch, but it's > > probably overkill. > > The only case I can imagine something going wrong is if this series is > only applied halfway, and another series bumps the maximum feature to > something that includes NV. I guess your suggestion would solve that. I won't lose sleep over it either way. Cheers ---Dave
