Subject: [PATCH v2 12/21] arm64: KVM: Implement fpsimd save/restore

From: [email-masked] (Christoffer Dall)
Date: Wed, 2 Dec 2015 17:19:56 +0100

On Wed, Dec 02, 2015 at 03:29:50PM +0000, Marc Zyngier wrote:
> On 02/12/15 11:53, Christoffer Dall wrote:
> > On Fri, Nov 27, 2015 at 06:50:06PM +0000, Marc Zyngier 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       |  7 +++++++
> >>  arch/arm64/kvm/hyp/switch.c    |  8 ++++++++
> >>  arch/arm64/kvm/hyp/sysreg-sr.c |  2 +-
> >>  6 files changed, 81 insertions(+), 2 deletions(-)
> >>  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
> > 
> > nit: Add a comment along the lines of:
> > // Skip restoring fpexc32 for AArch64 guests
> > 
> >> +	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 f0427ee..18365dd 100644
> >> --- a/arch/arm64/kvm/hyp/hyp.h
> >> +++ b/arch/arm64/kvm/hyp/hyp.h
> >> @@ -66,6 +66,13 @@ void __debug_restore_state(struct kvm_vcpu *vcpu,
> >>  void __debug_cond_save_host_state(struct kvm_vcpu *vcpu);
> >>  void __debug_cond_restore_host_state(struct kvm_vcpu *vcpu);
> >>  
> >> +void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
> >> +void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
> >> +static inline bool __fpsimd_enabled(void)
> >> +{
> >> +	return !(read_sysreg(cptr_el2) & CPTR_EL2_TFP);
> >> +}
> >> +
> >>  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 d67ed9e..8affc19 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 = __fpsimd_enabled();
> >> +
> > 
> > what does 'enabled' really mean here?  Isn't it really
> > __fpsimd_is_dirty() or __fpsimd_is_guest() or something like that (I
> > suck at naming too).
> 
> It really means "the FP regs are accessible and won't explode in your
> face". It doesn't necessary means dirty (though that's the way we use it
> below.
> 
> Your call, really.
> 
meh, it's fine the way it is.  Enabled for the guest I suppose is valid
enough :)

-Christoffer