On Fri, Nov 17, 2017 at 04:38:54PM +0000, Dave Martin wrote: > Currently, SVE use can remain untrapped if a KVM vcpu thread is > preempted inside the kernel and we then switch back to some user > thread. > > This patch ensures that SVE traps for userspace are enabled before > switching away from the vcpu thread. I don't really understand why KVM is any different then any other thread which could be using SVE that gets preempted? > > In an attempt to preserve some clarity about why and when this is > needed, kvm_fpsimd_flush_cpu_state() is used as a hook for doing > this. This means that this function needs to be called after > exiting the vcpu instead of before entry: I don't understand why the former means the latter? > this patch moves the call > as appropriate. As a side-effect, this will avoid the call if vcpu > entry is shortcircuited by a signal etc. > > Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx> > --- > arch/arm64/kernel/fpsimd.c | 2 ++ > virt/kvm/arm/arm.c | 6 +++--- > 2 files changed, 5 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > index 3dc8058..3b135eb 100644 > --- a/arch/arm64/kernel/fpsimd.c > +++ b/arch/arm64/kernel/fpsimd.c > @@ -1083,6 +1083,8 @@ void sve_flush_cpu_state(void) > > if (last->st && last->sve_in_use) > fpsimd_flush_cpu_state(); > + > + sve_user_disable(); > } > #endif /* CONFIG_ARM64_SVE */ > > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c > index 772bf74..554b157 100644 > --- a/virt/kvm/arm/arm.c > +++ b/virt/kvm/arm/arm.c > @@ -651,9 +651,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) > */ > preempt_disable(); > > - /* Flush FP/SIMD state that can't survive guest entry/exit */ > - kvm_fpsimd_flush_cpu_state(); > - > kvm_pmu_flush_hwstate(vcpu); > > local_irq_disable(); > @@ -754,6 +751,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) > guest_exit(); > trace_kvm_exit(ret, kvm_vcpu_trap_get_class(vcpu), *vcpu_pc(vcpu)); > > + /* Flush FP/SIMD state that can't survive guest entry/exit */ > + kvm_fpsimd_flush_cpu_state(); > + Could this be done in kvm_arch_vcpu_put() instead? > preempt_enable(); > > ret = handle_exit(vcpu, run, ret); > -- > 2.1.4 > Thanks, -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
