On Thu, Apr 04, 2019 at 04:17:24AM +0100, Marc Zyngier wrote: > On Wed, 03 Apr 2019 20:14:13 +0100, > Andrew Jones <[email protected]> wrote: > > > > On Fri, Mar 29, 2019 at 01:00:34PM +0000, Dave Martin wrote: > > > Since SVE will be enabled or disabled on a per-vcpu basis, a flag > > > is needed in order to track which vcpus have it enabled. > > > > > > This patch adds a suitable flag and a helper for checking it. > > > > > > Signed-off-by: Dave Martin <[email protected]> > > > Reviewed-by: Alex Bennée <[email protected]> > > > Tested-by: zhang.lei <[email protected]> > > > --- > > > arch/arm64/include/asm/kvm_host.h | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/arch/arm64/include/asm/kvm_host.h > > > b/arch/arm64/include/asm/kvm_host.h > > > index 6d10100..ad4f7f0 100644 > > > --- a/arch/arm64/include/asm/kvm_host.h > > > +++ b/arch/arm64/include/asm/kvm_host.h > > > @@ -328,6 +328,10 @@ struct kvm_vcpu_arch { > > > #define KVM_ARM64_FP_HOST (1 << 2) /* host FP regs loaded > > > */ > > > #define KVM_ARM64_HOST_SVE_IN_USE (1 << 3) /* backup for host > > > TIF_SVE */ > > > #define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0 > > > */ > > > +#define KVM_ARM64_GUEST_HAS_SVE (1 << 5) /* SVE exposed to > > > guest */ > > > + > > > +#define vcpu_has_sve(vcpu) (system_supports_sve() && \ > > > + ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE)) > > > > We shouldn't need the system_supports_sve() here. vcpu->arch.flags can > > only have the KVM_ARM64_GUEST_HAS_SVE flag set when system_supports_sve() > > is true, and it can't change later. > > This is a performance optimisation. system_supports_sve() results in a > static key being emitted, and that avoids a number of loads on the > fast path for non-SVE systems (which is likely to be the absolute > majority for the foreseeable future).
Exactly so. The same applies to many of the other call sites for system_supports_sve(). Cheers ---Dave _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
