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SubjectRe: [PATCH v1 2/2] kvm: arm64: handle single-step of hyp emulated mmio instructions
On Thu, Nov 23, 2017 at 12:11:34PM +0000, Alex Bennée wrote:
> There is a fast-path of MMIO emulation inside hyp mode. The handling
> of single-step is broadly the same as kvm_arm_handle_step_debug()
> except we just setup ESR/HSR so handle_exit() does the correct thing
> as we exit.
>
> For the case of an emulated illegal access causing an SError we will
> exit via the ARM_EXCEPTION_EL1_SERROR path in handle_exit(). We behave
> as we would during a real SError and clear the DBG_SPSR_SS bit for the
> emulated instruction.
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
> arch/arm64/kvm/hyp/switch.c | 37 ++++++++++++++++++++++++++++++-------
> 1 file changed, 30 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 525c01f48867..f7c651f3a8c0 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -22,6 +22,7 @@
> #include <asm/kvm_emulate.h>
> #include <asm/kvm_hyp.h>
> #include <asm/fpsimd.h>
> +#include <asm/debug-monitors.h>
>
> static bool __hyp_text __fpsimd_enabled_nvhe(void)
> {
> @@ -269,7 +270,11 @@ static bool __hyp_text __populate_fault_info(struct kvm_vcpu *vcpu)
> return true;
> }
>
> -static void __hyp_text __skip_instr(struct kvm_vcpu *vcpu)
> +/* Skip an instruction which has been emulated. Returns true if
> + * execution can continue or false if we need to exit hyp mode because
> + * single-step was in effect.
> + */
> +static bool __hyp_text __skip_instr(struct kvm_vcpu *vcpu)
> {
> *vcpu_pc(vcpu) = read_sysreg_el2(elr);
>
> @@ -282,6 +287,14 @@ static void __hyp_text __skip_instr(struct kvm_vcpu *vcpu)
> }
>
> write_sysreg_el2(*vcpu_pc(vcpu), elr);
> +
> + if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
> + vcpu->arch.fault.esr_el2 =
> + (ESR_ELx_EC_SOFTSTP_LOW << ESR_ELx_EC_SHIFT) | 0x22;
> + return false;
> + } else {
> + return true;
> + }
> }
>
> int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> @@ -342,13 +355,21 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> int ret = __vgic_v2_perform_cpuif_access(vcpu);
>
> if (ret == 1) {
> - __skip_instr(vcpu);
> - goto again;
> + if (__skip_instr(vcpu))
> + goto again;
> + else
> + exit_code = ARM_EXCEPTION_TRAP;
> }
>
> if (ret == -1) {
> - /* Promote an illegal access to an SError */
> - __skip_instr(vcpu);
> + /* Promote an illegal access to an
> + * SError. If we would be returning
> + * due to single-step clear the SS
> + * bit so handle_exit knows what to
> + * do after dealing with the error.
> + */
> + if (!__skip_instr(vcpu))
> + *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
> exit_code = ARM_EXCEPTION_EL1_SERROR;
> }
>
> @@ -363,8 +384,10 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> int ret = __vgic_v3_perform_cpuif_access(vcpu);
>
> if (ret == 1) {
> - __skip_instr(vcpu);
> - goto again;
> + if (__skip_instr(vcpu))
> + goto again;
> + else
> + exit_code = ARM_EXCEPTION_TRAP;
> }
>
> /* 0 falls through to be handled out of EL2 */
> --
> 2.15.0
>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>

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