Hi Dave,
On Mon, Apr 09, 2018 at 11:53:02AM +0100, Dave Martin wrote:
> This patch refactors KVM to align the host and guest FPSIMD
> save/restore logic with each other for arm64. This reduces the
> number of redundant save/restore operations that must occur, and
> reduces the common-case IRQ blackout time during guest exit storms
> by saving the host state lazily and optimising away the need to
> restore the host state before returning to the run loop.
>
[...]
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index db08a54..74c5a46 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
[...]
> @@ -1054,15 +1066,20 @@ void fpsimd_update_current_state(struct
> user_fpsimd_state const *state)
> local_bh_enable();
> }
>
> +void fpsimd_flush_state(unsigned int *cpu)
This API looks strange to me, and doesn't seem to be called from
elsewhere. Wouldn't it be more clear if it took a struct thread_struct
pointer instead, or if the logic remained embedded in
fpsimd_flush_task_state ?
> +{
> + *cpu = NR_CPUS;
> +}
> +
> /*
> * Invalidate live CPU copies of task t's FPSIMD state
> */
> void fpsimd_flush_task_state(struct task_struct *t)
> {
> - t->thread.fpsimd_cpu = NR_CPUS;
> + fpsimd_flush_state(&t->thread.fpsimd_cpu);
> }
>
> -static inline void fpsimd_flush_cpu_state(void)
> +void fpsimd_flush_cpu_state(void)
> {
> __this_cpu_write(fpsimd_last_state.st, NULL);
> }
[...]
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 8605e04..797b259 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -27,6 +27,7 @@
> #include <asm/kvm_mmu.h>
> #include <asm/fpsimd.h>
> #include <asm/debug-monitors.h>
> +#include <asm/thread_info.h>
>
> static bool __hyp_text __fpsimd_enabled_nvhe(void)
> {
> @@ -47,24 +48,40 @@ bool __hyp_text __fpsimd_enabled(void)
> return __fpsimd_is_enabled()();
> }
>
> -static void __hyp_text __activate_traps_vhe(void)
> +static bool update_fp_enabled(struct kvm_vcpu *vcpu)
I think this needs a __hyp_text in the unlikely case that this function
is not inlined in the _nvhe caller by the compiler.
> +{
> + if (vcpu->arch.host_thread_info->flags & _TIF_FOREIGN_FPSTATE) {
> + vcpu->arch.host_fpsimd_state = NULL;
> + vcpu->arch.fp_enabled = false;
> + }
I'm not clear why the above logic can't go into kvm_arch_vcpu_load_fp
and why we can't simply check TIF_FOREIGN_FPSTATE in __hyp_switch_fpsimd
instead?
> +
> + return vcpu->arch.fp_enabled;
> +}
> +
> +static void __hyp_text __activate_traps_vhe(struct kvm_vcpu *vcpu)
> {
> u64 val;
>
> val = read_sysreg(cpacr_el1);
> val |= CPACR_EL1_TTA;
> - val &= ~(CPACR_EL1_FPEN | CPACR_EL1_ZEN);
> + val &= ~CPACR_EL1_ZEN;
> + if (!update_fp_enabled(vcpu))
> + val &= ~CPACR_EL1_FPEN;
> +
> write_sysreg(val, cpacr_el1);
>
> write_sysreg(kvm_get_hyp_vector(), vbar_el1);
> }
>
> -static void __hyp_text __activate_traps_nvhe(void)
> +static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)
> {
> u64 val;
>
> val = CPTR_EL2_DEFAULT;
> - val |= CPTR_EL2_TTA | CPTR_EL2_TFP | CPTR_EL2_TZ;
> + val |= CPTR_EL2_TTA | CPTR_EL2_TZ;
> + if (!update_fp_enabled(vcpu))
> + val |= CPTR_EL2_TFP;
> +
> write_sysreg(val, cptr_el2);
> }
>
[...]
Otherwise this approach looks quite good to me overall. Are you
planning to add SVE support before removing the RFC from this series?
Thanks,
-Christoffer
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
