On 21/06/2019 10:37, Marc Zyngier wrote: > From: Jintack Lim <jintack.lim@xxxxxxxxxx> > > Add a new ARM64_HAS_NESTED_VIRT feature to indicate that the > CPU has the ARMv8.3 nested virtualization capability. > > This will be used to support nested virtualization in KVM. > > Signed-off-by: Jintack Lim <jintack.lim@xxxxxxxxxx> > Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx> > Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxx> > Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> > --- > .../admin-guide/kernel-parameters.txt | 4 +++ > arch/arm64/include/asm/cpucaps.h | 3 ++- > arch/arm64/include/asm/sysreg.h | 1 + > arch/arm64/kernel/cpufeature.c | 26 +++++++++++++++++++ > 4 files changed, 33 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 138f6664b2e2..202bb2115d83 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -2046,6 +2046,10 @@ > [KVM,ARM] Allow use of GICv4 for direct injection of > LPIs. > > + kvm-arm.nested= > + [KVM,ARM] Allow nested virtualization in KVM/ARM. > + Default is 0 (disabled) > + Once the kernel has been built with nested guest support, what do we gain from having it disabled by default? It seems a bit odd since the guests have to opt-in for the capability of running guests of their own. Is it it likely to have negative impact a negative impact on the host kernel? Or on guests that do not request use of nested virt? If not I feel that this kernel parameter should be dropped. Cheers, -- Julien Thierry
