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

From: [email-masked] (Marc Zyngier)
Date: Tue, 17 Nov 2015 11:25:03 +0000

On 17/11/15 11:13, Steve Capper wrote:
> On 16 November 2015 at 13:11, Marc Zyngier <[email-masked]> wrote:
>> Implement the fpsimd save restore, keeping the lazy part in
>> assembler (as returning to C would be overkill).
>>
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  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 <[email-masked]>
>> + *
>> + * 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).

Yeah, it looks like I screwed up in the base code, and somewhat fixed it
in the VHE branch... And as I'm testing the full setup, I didn't spot
it, sorry.

Can you please give the kvm-arm64/vhe-wsinc branch a spin and let me
know if it works for you?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...