Re: [PATCH v2 2/4] KVM: arm64: sefltests: Add helpers for guest hypervisors

[Itaru Kitayama]

On Sun, Apr 12, 2026 at 03:22:14PM +0100, Wei-Lin Chang wrote:
> Add helpers so that guest hypervisors can run nested guests. SP_EL1
> save/restore is added to allow nested guests to use a stack.
> 
> Signed-off-by: Wei-Lin Chang <weilin.chang@xxxxxxx>
> ---
>  .../selftests/kvm/include/arm64/nested.h      | 17 +++++++
>  tools/testing/selftests/kvm/lib/arm64/entry.S |  5 ++
>  .../testing/selftests/kvm/lib/arm64/nested.c  | 46 +++++++++++++++++++
>  3 files changed, 68 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/arm64/nested.h b/tools/testing/selftests/kvm/include/arm64/nested.h
> index 86d931facacb..7928ef89494a 100644
> --- a/tools/testing/selftests/kvm/include/arm64/nested.h
> +++ b/tools/testing/selftests/kvm/include/arm64/nested.h
> @@ -21,8 +21,17 @@
>  
>  extern char hyp_vectors[];
>  
> +enum vcpu_sysreg {
> +	__INVALID_SYSREG__,   /* 0 is reserved as an invalid value */
> +
> +	SP_EL1,
> +
> +	NR_SYS_REGS
> +};
> +
>  struct cpu_context {
>  	struct user_pt_regs regs;	/* sp = sp_el0 */
> +	u64 sys_regs[NR_SYS_REGS];
>  };
>  
>  struct vcpu {
> @@ -37,9 +46,17 @@ struct hyp_data {
>  	struct cpu_context hyp_context;
>  };

I am not sure of these structs you introduced only for nested guest feature
testing, as the KVM arm64 code they are quite complex and involved, 
extracring part of those and add members as hello_nested or simliar
tests evolve, then add test cases to me seems fragile. 
But if you have strong reason to add these would you mind explaining a bit?

Thanks,
Itaru.

>  
> +void prepare_hyp(void);
> +void init_vcpu(struct vcpu *vcpu, vm_paddr_t l2_pc, vm_paddr_t l2_stack_top);
> +int run_l2(struct vcpu *vcpu, struct hyp_data *hyp_data);
> +
> +void do_hvc(void);
>  u64 __guest_enter(struct vcpu *vcpu, struct cpu_context *hyp_context);
>  void __hyp_exception(u64 type);
>  
> +void __sysreg_save_el1_state(struct cpu_context *ctxt);
> +void __sysreg_restore_el1_state(struct cpu_context *ctxt);
> +
>  #endif /* !__ASSEMBLER__ */
>  
>  #endif /* SELFTEST_KVM_NESTED_H */
> diff --git a/tools/testing/selftests/kvm/lib/arm64/entry.S b/tools/testing/selftests/kvm/lib/arm64/entry.S
> index 33bedf5e7fb2..df3af3463c6c 100644
> --- a/tools/testing/selftests/kvm/lib/arm64/entry.S
> +++ b/tools/testing/selftests/kvm/lib/arm64/entry.S
> @@ -3,6 +3,11 @@
>   * adapted from arch/arm64/kvm/hyp/entry.S
>   */
>  
> + .globl do_hvc
> + do_hvc:
> +	hvc	#0
> +	ret
> +
>  /*
>   * Manually define these for now
>   */
> diff --git a/tools/testing/selftests/kvm/lib/arm64/nested.c b/tools/testing/selftests/kvm/lib/arm64/nested.c
> index 06ddaab2436f..b30d20b101c4 100644
> --- a/tools/testing/selftests/kvm/lib/arm64/nested.c
> +++ b/tools/testing/selftests/kvm/lib/arm64/nested.c
> @@ -4,7 +4,53 @@
>   */
>  
>  #include "nested.h"
> +#include "processor.h"
>  #include "test_util.h"
> +#include <asm/sysreg.h>
> +
> +void prepare_hyp(void)
> +{
> +	write_sysreg(HCR_EL2_E2H | HCR_EL2_RW, hcr_el2);
> +	write_sysreg(hyp_vectors, vbar_el2);
> +	isb();
> +}
> +
> +void init_vcpu(struct vcpu *vcpu, vm_paddr_t l2_pc, vm_paddr_t l2_stack_top)
> +{
> +	memset(vcpu, 0, sizeof(*vcpu));
> +	vcpu->context.regs.pc = l2_pc;
> +	vcpu->context.regs.pstate = PSR_MODE_EL1h | PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT;
> +	vcpu->context.sys_regs[SP_EL1] = l2_stack_top;
> +}
> +
> +void __sysreg_save_el1_state(struct cpu_context *ctxt)
> +{
> +	ctxt->sys_regs[SP_EL1] = read_sysreg(sp_el1);
> +}
> +
> +void __sysreg_restore_el1_state(struct cpu_context *ctxt)
> +{
> +	write_sysreg(ctxt->sys_regs[SP_EL1], sp_el1);
> +}
> +
> +int run_l2(struct vcpu *vcpu, struct hyp_data *hyp_data)
> +{
> +	u64 ret;
> +
> +	__sysreg_restore_el1_state(&vcpu->context);
> +
> +	write_sysreg(vcpu->context.regs.pstate, spsr_el2);
> +	write_sysreg(vcpu->context.regs.pc, elr_el2);
> +
> +	ret =  __guest_enter(vcpu, &hyp_data->hyp_context);
> +
> +	vcpu->context.regs.pc = read_sysreg(elr_el2);
> +	vcpu->context.regs.pstate = read_sysreg(spsr_el2);
> +
> +	__sysreg_save_el1_state(&vcpu->context);
> +
> +	return ret;
> +}
>  
>  void __hyp_exception(u64 type)
>  {
> -- 
> 2.43.0
>