[PATCH 12/21] arm64: KVM: Implement fpsimd save/restore

Steve Capper steve.capper at linaro.org
Tue Nov 17 03:13:18 PST 2015


On 16 November 2015 at 13:11, Marc Zyngier <marc.zyngier at arm.com> wrote:
> Implement the fpsimd save restore, keeping the lazy part in
> assembler (as returning to C would be overkill).
>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
>  arch/arm64/kvm/hyp/Makefile |  1 +
>  arch/arm64/kvm/hyp/entry.S  | 32 +++++++++++++++++++++++++++++++-
>  arch/arm64/kvm/hyp/fpsimd.S | 33 +++++++++++++++++++++++++++++++++
>  arch/arm64/kvm/hyp/hyp.h    |  3 +++
>  arch/arm64/kvm/hyp/switch.c |  8 ++++++++
>  5 files changed, 76 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/kvm/hyp/fpsimd.S
>
> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
> index 9c11b0f..56238d0 100644
> --- a/arch/arm64/kvm/hyp/Makefile
> +++ b/arch/arm64/kvm/hyp/Makefile
> @@ -9,3 +9,4 @@ obj-$(CONFIG_KVM_ARM_HOST) += sysreg-sr.o
>  obj-$(CONFIG_KVM_ARM_HOST) += debug-sr.o
>  obj-$(CONFIG_KVM_ARM_HOST) += entry.o
>  obj-$(CONFIG_KVM_ARM_HOST) += switch.o
> +obj-$(CONFIG_KVM_ARM_HOST) += fpsimd.o
> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> index 2c4449a..7552922 100644
> --- a/arch/arm64/kvm/hyp/entry.S
> +++ b/arch/arm64/kvm/hyp/entry.S
> @@ -27,6 +27,7 @@
>
>  #define CPU_GP_REG_OFFSET(x)   (CPU_GP_REGS + x)
>  #define CPU_XREG_OFFSET(x)     CPU_GP_REG_OFFSET(CPU_USER_PT_REGS + 8*x)
> +#define CPU_SYSREG_OFFSET(x)   (CPU_SYSREGS + 8*x)
>
>         .text
>         .pushsection    .hyp.text, "ax"
> @@ -152,4 +153,33 @@ ENTRY(__guest_exit)
>         ret
>  ENDPROC(__guest_exit)
>
> -       /* Insert fault handling here */
> +ENTRY(__fpsimd_guest_restore)
> +       push    x4, lr
> +
> +       mrs     x2, cptr_el2
> +       bic     x2, x2, #CPTR_EL2_TFP
> +       msr     cptr_el2, x2
> +       isb
> +
> +       mrs     x3, tpidr_el2
> +
> +       ldr     x0, [x3, #VCPU_HOST_CONTEXT]
> +       kern_hyp_va x0
> +       add     x0, x0, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
> +       bl      __fpsimd_save_state
> +
> +       add     x2, x3, #VCPU_CONTEXT
> +       add     x0, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
> +       bl      __fpsimd_restore_state
> +
> +       mrs     x1, hcr_el2
> +       tbnz    x1, #HCR_RW_SHIFT, 1f
> +       ldr     x4, [x2, #CPU_SYSREG_OFFSET(FPEXC32_EL2)]
> +       msr     fpexc32_el2, x4
> +1:
> +       pop     x4, lr
> +       pop     x2, x3
> +       pop     x0, x1
> +
> +       eret
> +ENDPROC(__fpsimd_guest_restore)
> diff --git a/arch/arm64/kvm/hyp/fpsimd.S b/arch/arm64/kvm/hyp/fpsimd.S
> new file mode 100644
> index 0000000..da3f22c
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/fpsimd.S
> @@ -0,0 +1,33 @@
> +/*
> + * Copyright (C) 2015 - ARM Ltd
> + * Author: Marc Zyngier <marc.zyngier at arm.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/linkage.h>
> +
> +#include <asm/fpsimdmacros.h>
> +
> +       .text
> +       .pushsection    .hyp.text, "ax"
> +
> +ENTRY(__fpsimd_save_state)
> +       fpsimd_save     x0, 1
> +       ret
> +ENDPROC(__fpsimd_save_state)
> +
> +ENTRY(__fpsimd_restore_state)
> +       fpsimd_restore  x0, 1
> +       ret
> +ENDPROC(__fpsimd_restore_state)
> diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
> index bf13238..240fb79 100644
> --- a/arch/arm64/kvm/hyp/hyp.h
> +++ b/arch/arm64/kvm/hyp/hyp.h
> @@ -70,6 +70,9 @@ void __debug_clear_restore_state(struct kvm_vcpu *vcpu,
>                                  struct kvm_guest_debug_arch *dbg,
>                                  struct kvm_cpu_context *ctxt);
>
> +void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
> +void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
> +
>  u64 __guest_enter(struct kvm_vcpu *vcpu, struct kvm_cpu_context *host_ctxt);
>
>  #endif /* __ARM64_KVM_HYP_H__ */
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index a3af81a..06d3e20 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -88,6 +88,7 @@ int __hyp_text __guest_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);
> @@ -117,6 +118,8 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
>         exit_code = __guest_enter(vcpu, host_ctxt);
>         /* And we're baaack! */
>
> +       fp_enabled = !!(read_sysreg(cptr_el2) & CPTR_EL2_TFP);

Should this not be a single logical not?
If CPTR_EL2_TFP is set then the floating point will trap in the guest,
thus floating point hasn't been used by the guest?

I am chasing some issues when running kvmtool on my system with this
patch set applied.
The above change stops NetworkManager crashing on my host.

Unfortunately I am still chasing some problems with the guest (illegal
instructions).

> +
>         __sysreg_save_state(guest_ctxt);
>         __sysreg32_save_state(vcpu);
>         __timer_save_state(vcpu);
> @@ -127,6 +130,11 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
>
>         __sysreg_restore_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, &vcpu->arch.vcpu_debug_state, guest_ctxt);
>         __debug_clear_restore_state(vcpu, &vcpu->arch.host_debug_state, host_ctxt);
>
> --
> 2.1.4
>
> _______________________________________________
> kvmarm mailing list
> kvmarm at lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm



More information about the linux-arm-kernel mailing list