[PATCH 08/37] KVM: arm64: Defer restoring host VFP state to vcpu_put
Andrew Jones
drjones at redhat.com
Tue Nov 7 05:15:50 PST 2017
On Thu, Oct 12, 2017 at 12:41:12PM +0200, Christoffer Dall wrote:
> Avoid saving the guest VFP registers and restoring the host VFP
> registers on every exit from the VM. Only when we're about to run
> userspace or other threads in the kernel do we really have to switch the
> state back to the host state.
>
> We still initially configure the VFP registers to trap when entering the
> VM, but the difference is that we now leave the guest state in the
> hardware registers while running the VM.
running the host.
>
> Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> ---
> arch/arm64/include/asm/kvm_emulate.h | 5 ++++
> arch/arm64/include/asm/kvm_host.h | 3 +++
> arch/arm64/kernel/asm-offsets.c | 1 +
> arch/arm64/kvm/hyp/entry.S | 3 +++
> arch/arm64/kvm/hyp/switch.c | 47 +++++++++++-------------------------
> arch/arm64/kvm/hyp/sysreg-sr.c | 21 +++++++++++++---
> 6 files changed, 44 insertions(+), 36 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 1fbfe96..630dd60 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -56,6 +56,11 @@ static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
> return (unsigned long *)&vcpu->arch.hcr_el2;
> }
>
> +static inline bool vcpu_el1_is_32bit(struct kvm_vcpu *vcpu)
> +{
> + return (!(vcpu->arch.hcr_el2 & HCR_RW));
nit: no need for the outer ().
> +}
> +
> static inline unsigned long *vcpu_pc(const struct kvm_vcpu *vcpu)
> {
> return (unsigned long *)&vcpu_gp_regs(vcpu)->regs.pc;
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 7d3bfa7..5e09eb9 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -210,6 +210,9 @@ struct kvm_vcpu_arch {
> /* Guest debug state */
> u64 debug_flags;
>
> + /* 1 if the guest VFP state is loaded into the hardware */
> + u64 guest_vfp_loaded;
> +
Is there a chance we'll want other flags like this? Should we just make
this a lazy state flags field with the (currently only) flag VFP? If not,
then a bool would be nicer, although I see below the u64 was chosen in
order for the 'str' to be used.
> /*
> * We maintain more than a single set of debug registers to support
> * debugging the guest from the host and to maintain separate host and
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 612021d..9946732 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -133,6 +133,7 @@ int main(void)
> DEFINE(CPU_GP_REGS, offsetof(struct kvm_cpu_context, gp_regs));
> DEFINE(CPU_USER_PT_REGS, offsetof(struct kvm_regs, regs));
> DEFINE(CPU_FP_REGS, offsetof(struct kvm_regs, fp_regs));
> + DEFINE(VCPU_GUEST_VFP_LOADED, offsetof(struct kvm_vcpu, arch.guest_vfp_loaded));
> DEFINE(VCPU_FPEXC32_EL2, offsetof(struct kvm_vcpu, arch.ctxt.sys_regs[FPEXC32_EL2]));
> DEFINE(VCPU_HOST_CONTEXT, offsetof(struct kvm_vcpu, arch.host_cpu_context));
> DEFINE(HOST_CONTEXT_VCPU, offsetof(struct kvm_cpu_context, __hyp_running_vcpu));
> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> index 76cd48f..b3e7191 100644
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -185,6 +185,9 @@ alternative_endif
> add x0, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
> bl __fpsimd_restore_state
>
> + mov x0, #1
> + str x0, [x3, #VCPU_GUEST_VFP_LOADED]
> +
> // Skip restoring fpexc32 for AArch64 guests
> mrs x1, hcr_el2
> tbnz x1, #HCR_RW_SHIFT, 1f
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 7703d63..ef05c59 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -23,43 +23,31 @@
> #include <asm/kvm_hyp.h>
> #include <asm/fpsimd.h>
>
> -static bool __hyp_text __fpsimd_enabled_nvhe(void)
> -{
> - return !(read_sysreg(cptr_el2) & CPTR_EL2_TFP);
> -}
> -
> -static bool __hyp_text __fpsimd_enabled_vhe(void)
> -{
> - return !!(read_sysreg(cpacr_el1) & CPACR_EL1_FPEN);
> -}
> -
> -static hyp_alternate_select(__fpsimd_is_enabled,
> - __fpsimd_enabled_nvhe, __fpsimd_enabled_vhe,
> - ARM64_HAS_VIRT_HOST_EXTN);
> -
> -bool __hyp_text __fpsimd_enabled(void)
> -{
> - return __fpsimd_is_enabled()();
> -}
> -
> -static void __hyp_text __activate_traps_vhe(void)
> +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;
> + if (vcpu->arch.guest_vfp_loaded)
> + val |= CPACR_EL1_FPEN;
> + else
> + val &= ~CPACR_EL1_FPEN;
> write_sysreg(val, cpacr_el1);
>
> write_sysreg(__kvm_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;
> + val |= CPTR_EL2_TTA;
> + if (vcpu->arch.guest_vfp_loaded)
> + val &= ~CPTR_EL2_TFP;
> + else
> + val |= CPTR_EL2_TFP;
> write_sysreg(val, cptr_el2);
> }
>
> @@ -81,7 +69,8 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
> * it will cause an exception.
> */
> val = vcpu->arch.hcr_el2;
> - if (!(val & HCR_RW) && system_supports_fpsimd()) {
> + if (vcpu_el1_is_32bit(vcpu) && system_supports_fpsimd() &&
> + !vcpu->arch.guest_vfp_loaded) {
> write_sysreg(1 << 30, fpexc32_el2);
> isb();
> }
> @@ -97,7 +86,7 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
> write_sysreg(0, pmselr_el0);
> write_sysreg(ARMV8_PMU_USERENR_MASK, pmuserenr_el0);
> write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
> - __activate_traps_arch()();
> + __activate_traps_arch()(vcpu);
> }
>
> static void __hyp_text __deactivate_traps_vhe(void)
> @@ -273,7 +262,6 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> {
> struct kvm_cpu_context *host_ctxt;
> struct kvm_cpu_context *guest_ctxt;
> - bool fp_enabled;
> u64 exit_code;
>
> vcpu = kern_hyp_va(vcpu);
> @@ -355,8 +343,6 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> /* 0 falls through to be handled out of EL2 */
> }
>
> - fp_enabled = __fpsimd_enabled();
> -
> __sysreg_save_guest_state(guest_ctxt);
> __sysreg32_save_state(vcpu);
> __timer_disable_traps(vcpu);
> @@ -367,11 +353,6 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>
> __sysreg_restore_host_state(host_ctxt);
>
> - if (fp_enabled) {
> - __fpsimd_save_state(&guest_ctxt->gp_regs.fp_regs);
> - __fpsimd_restore_state(&host_ctxt->gp_regs.fp_regs);
> - }
> -
> __debug_save_state(vcpu, kern_hyp_va(vcpu->arch.debug_ptr), guest_ctxt);
> /*
> * This must come after restoring the host sysregs, since a non-VHE
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> index b7438c8..c4a3714 100644
> --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> @@ -19,6 +19,7 @@
> #include <linux/kvm_host.h>
>
> #include <asm/kvm_asm.h>
> +#include <asm/kvm_emulate.h>
> #include <asm/kvm_hyp.h>
>
> /* Yes, this does nothing, on purpose */
> @@ -137,6 +138,11 @@ void __hyp_text __sysreg_restore_guest_state(struct kvm_cpu_context *ctxt)
> __sysreg_restore_common_state(ctxt);
> }
>
> +static void __hyp_text __fpsimd32_save_state(struct kvm_cpu_context *ctxt)
> +{
> + ctxt->sys_regs[FPEXC32_EL2] = read_sysreg(fpexc32_el2);
> +}
> +
> void __hyp_text __sysreg32_save_state(struct kvm_vcpu *vcpu)
> {
> u64 *spsr, *sysreg;
> @@ -155,9 +161,6 @@ void __hyp_text __sysreg32_save_state(struct kvm_vcpu *vcpu)
> sysreg[DACR32_EL2] = read_sysreg(dacr32_el2);
> sysreg[IFSR32_EL2] = read_sysreg(ifsr32_el2);
>
> - if (__fpsimd_enabled())
> - sysreg[FPEXC32_EL2] = read_sysreg(fpexc32_el2);
> -
> if (vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)
> sysreg[DBGVCR32_EL2] = read_sysreg(dbgvcr32_el2);
> }
> @@ -209,4 +212,16 @@ void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu)
> */
> void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu)
> {
> + struct kvm_cpu_context *host_ctxt = vcpu->arch.host_cpu_context;
> + struct kvm_cpu_context *guest_ctxt = &vcpu->arch.ctxt;
> +
> + /* Restore host FP/SIMD state */
> + if (vcpu->arch.guest_vfp_loaded) {
> + if (vcpu_el1_is_32bit(vcpu))
> + kvm_call_hyp(__fpsimd32_save_state,
> + kern_hyp_va(guest_ctxt));
nit: might be nice to use {} since we need two lines.
> + __fpsimd_save_state(&guest_ctxt->gp_regs.fp_regs);
> + __fpsimd_restore_state(&host_ctxt->gp_regs.fp_regs);
> + vcpu->arch.guest_vfp_loaded = 0;
> + }
> }
> --
> 2.9.0
>
Otherwise,
Reviewed-by: Andrew Jones <drjones at redhat.com>
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