Subject: [PATCH v3 07/22] arm64: KVM: Implement system register save/restore

From: [email-masked] (Mario Smarduch)
Date: Thu, 10 Dec 2015 19:24:59 -0800

Hi Marc,

On 12/7/2015 2:53 AM, Marc Zyngier wrote:
> Implement the system register save/restore as a direct translation of
> the assembly code version.
> 
> Signed-off-by: Marc Zyngier <[email-masked]>
> Reviewed-by: Christoffer Dall <[email-masked]>
> ---
>  arch/arm64/kvm/hyp/Makefile    |  1 +
>  arch/arm64/kvm/hyp/hyp.h       |  3 ++
>  arch/arm64/kvm/hyp/sysreg-sr.c | 90 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 94 insertions(+)
>  create mode 100644 arch/arm64/kvm/hyp/sysreg-sr.c
> 
> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
> index 455dc0a..ec94200 100644
> --- a/arch/arm64/kvm/hyp/Makefile
> +++ b/arch/arm64/kvm/hyp/Makefile
> @@ -5,3 +5,4 @@
>  obj-$(CONFIG_KVM_ARM_HOST) += vgic-v2-sr.o
>  obj-$(CONFIG_KVM_ARM_HOST) += vgic-v3-sr.o
>  obj-$(CONFIG_KVM_ARM_HOST) += timer-sr.o
> +obj-$(CONFIG_KVM_ARM_HOST) += sysreg-sr.o
> diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
> index f213e46..778d56d 100644
> --- a/arch/arm64/kvm/hyp/hyp.h
> +++ b/arch/arm64/kvm/hyp/hyp.h
> @@ -38,5 +38,8 @@ void __vgic_v3_restore_state(struct kvm_vcpu *vcpu);
>  void __timer_save_state(struct kvm_vcpu *vcpu);
>  void __timer_restore_state(struct kvm_vcpu *vcpu);
>  
> +void __sysreg_save_state(struct kvm_cpu_context *ctxt);
> +void __sysreg_restore_state(struct kvm_cpu_context *ctxt);
> +
>  #endif /* __ARM64_KVM_HYP_H__ */
>  
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> new file mode 100644
> index 0000000..add8fcb
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> @@ -0,0 +1,90 @@
> +/*
> + * Copyright (C) 2012-2015 - 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/compiler.h>
> +#include <linux/kvm_host.h>
> +
> +#include <asm/kvm_mmu.h>
> +
> +#include "hyp.h"
> +

I looked closer on some other ways to get better performance out of the
compiler. This code sequence performs about 35% faster for
__sysreg_save_state(..) for 5000 exits you save about 500mS or 100nS per exit.
This is on Juno.

register int volatile count asm("r2") = 0;

do {
....
} while(count);

I didn't test the restore function (ran out of time) but I suspect it should be
the same. The assembler pretty much uses all the GPRs, (a little too many, using
stp to push 4 pairs on the stack and restore) looking at the assembler it all
should execute out of order.

FWIW I gave this a try since compilers like to optimize loops. I used
'cntpct_el0' counter register to measure the intervals.

> +/* ctxt is already in the HYP VA space */
> +void __hyp_text __sysreg_save_state(struct kvm_cpu_context *ctxt)
> +{
> +	ctxt->sys_regs[MPIDR_EL1]	= read_sysreg(vmpidr_el2);
> +	ctxt->sys_regs[CSSELR_EL1]	= read_sysreg(csselr_el1);
> +	ctxt->sys_regs[SCTLR_EL1]	= read_sysreg(sctlr_el1);
> +	ctxt->sys_regs[ACTLR_EL1]	= read_sysreg(actlr_el1);
> +	ctxt->sys_regs[CPACR_EL1]	= read_sysreg(cpacr_el1);
> +	ctxt->sys_regs[TTBR0_EL1]	= read_sysreg(ttbr0_el1);
> +	ctxt->sys_regs[TTBR1_EL1]	= read_sysreg(ttbr1_el1);
> +	ctxt->sys_regs[TCR_EL1]		= read_sysreg(tcr_el1);
> +	ctxt->sys_regs[ESR_EL1]		= read_sysreg(esr_el1);
> +	ctxt->sys_regs[AFSR0_EL1]	= read_sysreg(afsr0_el1);
> +	ctxt->sys_regs[AFSR1_EL1]	= read_sysreg(afsr1_el1);
> +	ctxt->sys_regs[FAR_EL1]		= read_sysreg(far_el1);
> +	ctxt->sys_regs[MAIR_EL1]	= read_sysreg(mair_el1);
> +	ctxt->sys_regs[VBAR_EL1]	= read_sysreg(vbar_el1);
> +	ctxt->sys_regs[CONTEXTIDR_EL1]	= read_sysreg(contextidr_el1);
> +	ctxt->sys_regs[TPIDR_EL0]	= read_sysreg(tpidr_el0);
> +	ctxt->sys_regs[TPIDRRO_EL0]	= read_sysreg(tpidrro_el0);
> +	ctxt->sys_regs[TPIDR_EL1]	= read_sysreg(tpidr_el1);
> +	ctxt->sys_regs[AMAIR_EL1]	= read_sysreg(amair_el1);
> +	ctxt->sys_regs[CNTKCTL_EL1]	= read_sysreg(cntkctl_el1);
> +	ctxt->sys_regs[PAR_EL1]		= read_sysreg(par_el1);
> +	ctxt->sys_regs[MDSCR_EL1]	= read_sysreg(mdscr_el1);
> +
> +	ctxt->gp_regs.regs.sp		= read_sysreg(sp_el0);
> +	ctxt->gp_regs.regs.pc		= read_sysreg(elr_el2);
> +	ctxt->gp_regs.regs.pstate	= read_sysreg(spsr_el2);
> +	ctxt->gp_regs.sp_el1		= read_sysreg(sp_el1);
> +	ctxt->gp_regs.elr_el1		= read_sysreg(elr_el1);
> +	ctxt->gp_regs.spsr[KVM_SPSR_EL1]= read_sysreg(spsr_el1);
> +}
> +
> +void __hyp_text __sysreg_restore_state(struct kvm_cpu_context *ctxt)
> +{
> +	write_sysreg(ctxt->sys_regs[MPIDR_EL1],	  vmpidr_el2);
> +	write_sysreg(ctxt->sys_regs[CSSELR_EL1],  csselr_el1);
> +	write_sysreg(ctxt->sys_regs[SCTLR_EL1],	  sctlr_el1);
> +	write_sysreg(ctxt->sys_regs[ACTLR_EL1],	  actlr_el1);
> +	write_sysreg(ctxt->sys_regs[CPACR_EL1],	  cpacr_el1);
> +	write_sysreg(ctxt->sys_regs[TTBR0_EL1],	  ttbr0_el1);
> +	write_sysreg(ctxt->sys_regs[TTBR1_EL1],	  ttbr1_el1);
> +	write_sysreg(ctxt->sys_regs[TCR_EL1],	  tcr_el1);
> +	write_sysreg(ctxt->sys_regs[ESR_EL1],	  esr_el1);
> +	write_sysreg(ctxt->sys_regs[AFSR0_EL1],	  afsr0_el1);
> +	write_sysreg(ctxt->sys_regs[AFSR1_EL1],	  afsr1_el1);
> +	write_sysreg(ctxt->sys_regs[FAR_EL1],	  far_el1);
> +	write_sysreg(ctxt->sys_regs[MAIR_EL1],	  mair_el1);
> +	write_sysreg(ctxt->sys_regs[VBAR_EL1],	  vbar_el1);
> +	write_sysreg(ctxt->sys_regs[CONTEXTIDR_EL1], contextidr_el1);
> +	write_sysreg(ctxt->sys_regs[TPIDR_EL0],	  tpidr_el0);
> +	write_sysreg(ctxt->sys_regs[TPIDRRO_EL0], tpidrro_el0);
> +	write_sysreg(ctxt->sys_regs[TPIDR_EL1],	  tpidr_el1);
> +	write_sysreg(ctxt->sys_regs[AMAIR_EL1],	  amair_el1);
> +	write_sysreg(ctxt->sys_regs[CNTKCTL_EL1], cntkctl_el1);
> +	write_sysreg(ctxt->sys_regs[PAR_EL1],	  par_el1);
> +	write_sysreg(ctxt->sys_regs[MDSCR_EL1],	  mdscr_el1);
> +
> +	write_sysreg(ctxt->gp_regs.regs.sp,	sp_el0);
> +	write_sysreg(ctxt->gp_regs.regs.pc,	elr_el2);
> +	write_sysreg(ctxt->gp_regs.regs.pstate,	spsr_el2);
> +	write_sysreg(ctxt->gp_regs.sp_el1,	sp_el1);
> +	write_sysreg(ctxt->gp_regs.elr_el1,	elr_el1);
> +	write_sysreg(ctxt->gp_regs.spsr[KVM_SPSR_EL1], spsr_el1);
> +}
>