Re: [PATCH 12/13] arm64: KVM: Split sysreg save/restore

From: Christoffer Dall
Date: Mon Aug 31 2015 - 14:48:03 EST


On Wed, Jul 08, 2015 at 05:19:15PM +0100, Marc Zyngier wrote:
> As we're starting to get different requirements for non-VHE and VHE
> code paths, use a slightly more fine-grained approach:
>
> - __save/restore_sysregs: save/restore non-shared sysregs
> - __save/restore_shared_sysregs: save/restore only shared sysregs
>
> Of course, non-VHE always requires both.
>

I'm sorry, I don't really understand what this patch does.

What is a 'shared sysreg' exactly? One that is shared between the host
and the guest?

Or one that is shared between EL1 and EL2? Or is that the same thing?

> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
> arch/arm64/kvm/hyp.S | 91 +++++++++++++++++++++++++---------------------------
> 1 file changed, 44 insertions(+), 47 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index b61591b..3cbd2c4 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S
> @@ -280,11 +280,6 @@ skip_el1_restore:
> mrs x20, par_el1
> mrs x21, mdscr_el1
>
> - mrs x22, tpidr_el0
> - mrs x23, tpidrro_el0
> - mrs x24, tpidr_el1
> - mrs x25, actlr_el1
> -
> stp x4, x5, [x3]
> stp x6, x7, [x3, #16]
> stp x8, x9, [x3, #32]
> @@ -294,8 +289,6 @@ skip_el1_restore:
> stp x16, x17, [x3, #96]
> stp x18, x19, [x3, #112]
> stp x20, x21, [x3, #128]
> - stp x22, x23, [x3, #144]
> - stp x24, x25, [x3, #160]
> .endm
>
> .macro save_debug
> @@ -508,8 +501,6 @@ skip_el1_restore:
> ldp x16, x17, [x3, #96]
> ldp x18, x19, [x3, #112]
> ldp x20, x21, [x3, #128]
> - ldp x22, x23, [x3, #144]
> - ldp x24, x25, [x3, #160]
>
> msr vmpidr_el2, x4
> msr csselr_el1, x5
> @@ -529,11 +520,6 @@ skip_el1_restore:
> msr_el1(cntkctl, x19)
> msr par_el1, x20
> msr mdscr_el1, x21
> -
> - msr tpidr_el0, x22
> - msr tpidrro_el0, x23
> - msr tpidr_el1, x24
> - msr actlr_el1, x25
> .endm
>
> .macro restore_debug
> @@ -913,10 +899,12 @@ ifnvhe nop, "msr vbar_el1, x2"
>
> .macro save_timer_state
> // x0: vcpu pointer
> - ldr x2, [x0, #VCPU_KVM]
> - kern_hyp_va x2
> - ldr w3, [x2, #KVM_TIMER_ENABLED]
> - cbz w3, 1f
> + // x1: return code
> + // x2: vcpu context
> + ldr x3, [x0, #VCPU_KVM]
> + kern_hyp_va x3
> + ldr w4, [x3, #KVM_TIMER_ENABLED]
> + cbz w4, 1f
>
> mrs_el0(x3, cntv_ctl)
> and x3, x3, #3
> @@ -931,9 +919,9 @@ ifnvhe nop, "msr vbar_el1, x2"
>
> 1:
> // Allow physical timer/counter access for the host
> - mrs x2, cnthctl_el2
> - orr x2, x2, #3
> - msr cnthctl_el2, x2
> + mrs x3, cnthctl_el2
> + orr x3, x3, #3
> + msr cnthctl_el2, x3
>
> // Clear cntvoff for the host
> ifnvhe "msr cntvoff_el2, xzr", nop
> @@ -941,34 +929,43 @@ ifnvhe "msr cntvoff_el2, xzr", nop
>
> .macro restore_timer_state
> // x0: vcpu pointer
> + // x2: vcpu context
> // Disallow physical timer access for the guest
> // Physical counter access is allowed
> - mrs x2, cnthctl_el2
> - orr x2, x2, #1
> - bic x2, x2, #2
> - msr cnthctl_el2, x2
> -
> - ldr x2, [x0, #VCPU_KVM]
> - kern_hyp_va x2
> - ldr w3, [x2, #KVM_TIMER_ENABLED]
> - cbz w3, 1f
> -
> - ldr x3, [x2, #KVM_TIMER_CNTVOFF]
> - msr cntvoff_el2, x3
> - ldr x2, [x0, #VCPU_TIMER_CNTV_CVAL]
> - msr_el0(cntv_cval, x2)
> + mrs x3, cnthctl_el2
> + orr x3, x3, #1
> + bic x3, x3, #2
> + msr cnthctl_el2, x3
> +
> + ldr x3, [x0, #VCPU_KVM]
> + kern_hyp_va x3
> + ldr w4, [x3, #KVM_TIMER_ENABLED]
> + cbz w4, 1f
> +
> + ldr x4, [x3, #KVM_TIMER_CNTVOFF]
> + msr cntvoff_el2, x4
> + ldr x4, [x0, #VCPU_TIMER_CNTV_CVAL]
> + msr_el0(cntv_cval, x4)
> isb
>
> - ldr w2, [x0, #VCPU_TIMER_CNTV_CTL]
> - and x2, x2, #3
> - msr_el0(cntv_ctl, x2)
> + ldr w4, [x0, #VCPU_TIMER_CNTV_CTL]
> + and x4, x4, #3
> + msr_el0(cntv_ctl, x4)
> 1:
> .endm
>
> +__save_shared_sysregs:
> + save_shared_sysregs
> + ret
> +
> __save_sysregs:
> save_sysregs
> ret
>
> +__restore_shared_sysregs:
> + restore_shared_sysregs
> + ret
> +
> __restore_sysregs:
> restore_sysregs
> ret
> @@ -1010,10 +1007,9 @@ ENTRY(__kvm_vcpu_run)
>
> save_host_regs
> bl __save_fpsimd
> -ifnvhe "bl __save_sysregs", nop
> -ifnvhe "b 1f", nop
> - save_shared_sysregs
> -1:
> +ifnvhe "bl __save_sysregs", "nop"
> + bl __save_shared_sysregs
> +
> compute_debug_state 1f
> bl __save_debug
> 1:
> @@ -1027,6 +1023,7 @@ ifnvhe "b 1f", nop
> add x2, x0, #VCPU_CONTEXT
>
> bl __restore_sysregs
> + bl __restore_shared_sysregs
> bl __restore_fpsimd
>
> skip_debug_state x3, 1f
> @@ -1048,6 +1045,7 @@ __kvm_vcpu_return:
> save_guest_regs
> bl __save_fpsimd
> bl __save_sysregs
> + bl __save_shared_sysregs
>
> skip_debug_state x3, 1f
> bl __save_debug
> @@ -1064,10 +1062,8 @@ __kvm_vcpu_return:
> ldr x2, [x0, #VCPU_HOST_CONTEXT]
> kern_hyp_va x2
>
> -ifnvhe "bl __restore_sysregs", nop
> -ifnvhe "b 1f", nop
> - restore_shared_sysregs
> -1:
> +ifnvhe "bl __restore_sysregs", "nop"
> + bl __restore_shared_sysregs
> bl __restore_fpsimd
>
> skip_debug_state x3, 1f
> @@ -1159,7 +1155,8 @@ __kvm_hyp_panic:
> ldr x2, [x0, #VCPU_HOST_CONTEXT]
> kern_hyp_va x2
>
> - bl __restore_sysregs
> +ifnvhe "bl __restore_sysregs", "nop"
> + bl __restore_shared_sysregs
>
> 1: adr x0, __hyp_panic_str
> adr x1, 2f
> --
> 2.1.4
>
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