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SubjectRe: [RFC 08/55] KVM: arm64: Set virtual EL2 context depending on the guest exception level
On Mon, Jan 09, 2017 at 01:24:04AM -0500, Jintack Lim wrote:
> From: Christoffer Dall <christoffer.dall@linaro.org>
>
> Set up virutal EL2 context to hardware if the guest exception level is
> EL2.
>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> Signed-off-by: Jintack Lim <jintack@cs.columbia.edu>
> ---
> arch/arm64/kvm/context.c | 32 ++++++++++++++++++++++++++------
> 1 file changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/kvm/context.c b/arch/arm64/kvm/context.c
> index 320afc6..acb4b1e 100644
> --- a/arch/arm64/kvm/context.c
> +++ b/arch/arm64/kvm/context.c
> @@ -25,10 +25,25 @@
> void kvm_arm_setup_shadow_state(struct kvm_vcpu *vcpu)
> {
> struct kvm_cpu_context *ctxt = &vcpu->arch.ctxt;
> + if (unlikely(vcpu_mode_el2(vcpu))) {
> + ctxt->hw_pstate = *vcpu_cpsr(vcpu) & ~PSR_MODE_MASK;
>
> - ctxt->hw_pstate = *vcpu_cpsr(vcpu);
> - ctxt->hw_sys_regs = ctxt->sys_regs;
> - ctxt->hw_sp_el1 = ctxt->gp_regs.sp_el1;
> + /*
> + * We emulate virtual EL2 mode in hardware EL1 mode using the
> + * same stack pointer mode as the guest expects.
> + */

I think this comment should either be deleted or explain why this works
as opposed to stating the obvious. How about:

/*
* We can emulate the guest's configuration of which
* stack pointer to use when executing in virtual EL2 by
* using the equivalent feature in EL1 to point to
* either the EL1 or EL0 stack pointer.
*/

> + if ((*vcpu_cpsr(vcpu) & PSR_MODE_MASK) == PSR_MODE_EL2h)
> + ctxt->hw_pstate |= PSR_MODE_EL1h;
> + else
> + ctxt->hw_pstate |= PSR_MODE_EL1t;
> +
> + ctxt->hw_sys_regs = ctxt->shadow_sys_regs;
> + ctxt->hw_sp_el1 = ctxt->el2_regs[SP_EL2];
> + } else {
> + ctxt->hw_pstate = *vcpu_cpsr(vcpu);
> + ctxt->hw_sys_regs = ctxt->sys_regs;
> + ctxt->hw_sp_el1 = ctxt->gp_regs.sp_el1;
> + }
> }
>
> /**
> @@ -38,9 +53,14 @@ void kvm_arm_setup_shadow_state(struct kvm_vcpu *vcpu)
> void kvm_arm_restore_shadow_state(struct kvm_vcpu *vcpu)
> {
> struct kvm_cpu_context *ctxt = &vcpu->arch.ctxt;
> -
> - *vcpu_cpsr(vcpu) = ctxt->hw_pstate;
> - ctxt->gp_regs.sp_el1 = ctxt->hw_sp_el1;
> + if (unlikely(vcpu_mode_el2(vcpu))) {
> + *vcpu_cpsr(vcpu) &= PSR_MODE_MASK;
> + *vcpu_cpsr(vcpu) |= ctxt->hw_pstate & ~PSR_MODE_MASK;
> + ctxt->el2_regs[SP_EL2] = ctxt->hw_sp_el1;
> + } else {
> + *vcpu_cpsr(vcpu) = ctxt->hw_pstate;
> + ctxt->gp_regs.sp_el1 = ctxt->hw_sp_el1;
> + }
> }
>
> void kvm_arm_init_cpu_context(kvm_cpu_context_t *cpu_ctxt)
> --
> 1.9.1
>
>

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