[PATCH v2 15/36] KVM: arm64: Move userspace system registers into separate function

[Marc Zyngier]

On 07/12/17 17:06, Christoffer Dall wrote:
> There's a semantic difference between the EL1 registers that control
> operation of a kernel running in EL1 and EL1 registers that only control
> userspace execution in EL0.  Since we can defer saving/restoring the
> latter, move them into their own function.
> 
> We also take this chance to rename the function saving/restoring the
> remaining system register to make it clear this function deals with
> the EL1 system registers.
> 
> No functional change.
> 
> Reviewed-by: Andrew Jones <drjones at redhat.com>
> Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> ---
> 
> Notes:
>     Changes since v1:
>      - Added comment about sp_el0 to common save sysreg save/restore functions
> 
>  arch/arm64/kvm/hyp/sysreg-sr.c | 44 +++++++++++++++++++++++++++++++-----------
>  1 file changed, 33 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> index 68a7d164e5e1..bbfb4d01af88 100644
> --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> @@ -33,15 +33,24 @@ static void __hyp_text __sysreg_do_nothing(struct kvm_cpu_context *ctxt) { }
>   */
>  
>  static void __hyp_text __sysreg_save_common_state(struct kvm_cpu_context *ctxt)
> +{
> +	ctxt->sys_regs[MDSCR_EL1]	= read_sysreg(mdscr_el1);
> +
> +	/*
> +	 * The host arm64 Linux uses sp_el0 to point to 'current' and it must
> +	 * therefore be saved/restored on every entry/exit to/from the guest.
> +	 */
> +	ctxt->gp_regs.regs.sp		= read_sysreg(sp_el0);
> +}
> +
> +static void __hyp_text __sysreg_save_user_state(struct kvm_cpu_context *ctxt)
>  {
>  	ctxt->sys_regs[ACTLR_EL1]	= read_sysreg(actlr_el1);

What is the rational for keeping ACTLR_EL1 as part of the user state?

>  	ctxt->sys_regs[TPIDR_EL0]	= read_sysreg(tpidr_el0);
>  	ctxt->sys_regs[TPIDRRO_EL0]	= read_sysreg(tpidrro_el0);
> -	ctxt->sys_regs[MDSCR_EL1]	= read_sysreg(mdscr_el1);
> -	ctxt->gp_regs.regs.sp		= read_sysreg(sp_el0);
>  }
>  
> -static void __hyp_text __sysreg_save_state(struct kvm_cpu_context *ctxt)
> +static void __hyp_text __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
>  {
>  	ctxt->sys_regs[MPIDR_EL1]	= read_sysreg(vmpidr_el2);
>  	ctxt->sys_regs[CSSELR_EL1]	= read_sysreg(csselr_el1);
> @@ -70,31 +79,42 @@ static void __hyp_text __sysreg_save_state(struct kvm_cpu_context *ctxt)
>  }
>  
>  static hyp_alternate_select(__sysreg_call_save_host_state,
> -			    __sysreg_save_state, __sysreg_do_nothing,
> +			    __sysreg_save_el1_state, __sysreg_do_nothing,
>  			    ARM64_HAS_VIRT_HOST_EXTN);
>  
>  void __hyp_text __sysreg_save_host_state(struct kvm_cpu_context *ctxt)
>  {
>  	__sysreg_call_save_host_state()(ctxt);
>  	__sysreg_save_common_state(ctxt);
> +	__sysreg_save_user_state(ctxt);
>  }
>  
>  void __hyp_text __sysreg_save_guest_state(struct kvm_cpu_context *ctxt)
>  {
> -	__sysreg_save_state(ctxt);
> +	__sysreg_save_el1_state(ctxt);
>  	__sysreg_save_common_state(ctxt);
> +	__sysreg_save_user_state(ctxt);
>  }
>  
>  static void __hyp_text __sysreg_restore_common_state(struct kvm_cpu_context *ctxt)
>  {
> -	write_sysreg(ctxt->sys_regs[ACTLR_EL1],	  actlr_el1);
> -	write_sysreg(ctxt->sys_regs[TPIDR_EL0],	  tpidr_el0);
> -	write_sysreg(ctxt->sys_regs[TPIDRRO_EL0], tpidrro_el0);
>  	write_sysreg(ctxt->sys_regs[MDSCR_EL1],	  mdscr_el1);
> +
> +	/*
> +	 * The host arm64 Linux uses sp_el0 to point to 'current' and it must
> +	 * therefore be saved/restored on every entry/exit to/from the guest.
> +	 */
>  	write_sysreg(ctxt->gp_regs.regs.sp,	  sp_el0);
>  }
>  
> -static void __hyp_text __sysreg_restore_state(struct kvm_cpu_context *ctxt)
> +static void __hyp_text __sysreg_restore_user_state(struct kvm_cpu_context *ctxt)
> +{
> +	write_sysreg(ctxt->sys_regs[ACTLR_EL1],	  	actlr_el1);

Same here.

> +	write_sysreg(ctxt->sys_regs[TPIDR_EL0],	  	tpidr_el0);
> +	write_sysreg(ctxt->sys_regs[TPIDRRO_EL0], 	tpidrro_el0);
> +}
> +
> +static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
>  {
>  	write_sysreg(ctxt->sys_regs[MPIDR_EL1],		vmpidr_el2);
>  	write_sysreg(ctxt->sys_regs[CSSELR_EL1],	csselr_el1);
> @@ -123,19 +143,21 @@ static void __hyp_text __sysreg_restore_state(struct kvm_cpu_context *ctxt)
>  }
>  
>  static hyp_alternate_select(__sysreg_call_restore_host_state,
> -			    __sysreg_restore_state, __sysreg_do_nothing,
> +			    __sysreg_restore_el1_state, __sysreg_do_nothing,
>  			    ARM64_HAS_VIRT_HOST_EXTN);
>  
>  void __hyp_text __sysreg_restore_host_state(struct kvm_cpu_context *ctxt)
>  {
>  	__sysreg_call_restore_host_state()(ctxt);
>  	__sysreg_restore_common_state(ctxt);
> +	__sysreg_restore_user_state(ctxt);
>  }
>  
>  void __hyp_text __sysreg_restore_guest_state(struct kvm_cpu_context *ctxt)
>  {
> -	__sysreg_restore_state(ctxt);
> +	__sysreg_restore_el1_state(ctxt);
>  	__sysreg_restore_common_state(ctxt);
> +	__sysreg_restore_user_state(ctxt);
>  }
>  
>  static void __hyp_text __fpsimd32_save_state(struct kvm_cpu_context *ctxt)
> 

I think we should move ACTLR_EL1 to the EL1 state, allowing it to be
lazily switched. See the note in D10.2.1 that recommends a VHE enabled
system to have ACTLR_EL1 as a guest-only register.

Thanks,

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