Re: [PATCH v2 07/15] arm64: KVM: split debug save restore across vm/traps activation

Julien Thierry
2019-05-28T08:18:32Z

Hi Sudeep,

On 23/05/2019 11:34, Sudeep Holla wrote:
> If we enable profiling buffer controls at EL1 generate a trap exception
> to EL2, it also changes profiling buffer to use EL1&0 stage 1 translation
> regime in case of VHE. To support SPE both in the guest and host, we
> need to first stop profiling and flush the profiling buffers before
> we activate/switch vm or enable/disable the traps.
>
> In prepartion to do that, lets split the debug save restore functionality
> into 4 steps:
> 1. debug_save_host_context - saves the host context
> 2. debug_restore_guest_context - restore the guest context
> 3. debug_save_guest_context - saves the guest context
> 4. debug_restore_host_context - restores the host context
>
> Lets rename existing __debug_switch_to_{host,guest} to make sure it's
> aligned to the above and just add the place holders for new ones getting
> added here as we need them to support SPE in guests.
>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> ---
> arch/arm64/include/asm/kvm_hyp.h | 6 ++++--
> arch/arm64/kvm/hyp/debug-sr.c | 25 ++++++++++++++++---------
> arch/arm64/kvm/hyp/switch.c | 12 ++++++++----
> 3 files changed, 28 insertions(+), 15 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 782955db61dd..1c5ed80fcbda 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -164,8 +164,10 @@ void sysreg_restore_guest_state_vhe(struct kvm_cpu_context *ctxt);
> void __sysreg32_save_state(struct kvm_vcpu *vcpu);
> void __sysreg32_restore_state(struct kvm_vcpu *vcpu);
>
> -void __debug_switch_to_guest(struct kvm_vcpu *vcpu);
> -void __debug_switch_to_host(struct kvm_vcpu *vcpu);
> +void __debug_save_host_context(struct kvm_vcpu *vcpu);
> +void __debug_restore_guest_context(struct kvm_vcpu *vcpu);
> +void __debug_save_guest_context(struct kvm_vcpu *vcpu);
> +void __debug_restore_host_context(struct kvm_vcpu *vcpu);
>
> void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
> void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
> index fa51236ebcb3..618884df1dc4 100644
> --- a/arch/arm64/kvm/hyp/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/debug-sr.c
> @@ -149,20 +149,13 @@ static void __hyp_text __debug_restore_state(struct kvm_vcpu *vcpu,
> write_sysreg(ctxt->sys_regs[MDCCINT_EL1], mdccint_el1);
> }
>
> -void __hyp_text __debug_switch_to_guest(struct kvm_vcpu *vcpu)
> +void __hyp_text __debug_restore_guest_context(struct kvm_vcpu *vcpu)
> {
> struct kvm_cpu_context *host_ctxt;
> struct kvm_cpu_context *guest_ctxt;
> struct kvm_guest_debug_arch *host_dbg;
> struct kvm_guest_debug_arch *guest_dbg;
>
> - /*
> - * Non-VHE: Disable and flush SPE data generation
> - * VHE: The vcpu can run, but it can't hide.
> - */
> - if (!has_vhe())
> - __debug_save_spe_nvhe(&vcpu->arch.host_debug_state.pmscr_el1);
> -
> if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
> return;
>
> @@ -175,7 +168,7 @@ void __hyp_text __debug_switch_to_guest(struct kvm_vcpu *vcpu)
> __debug_restore_state(vcpu, guest_dbg, guest_ctxt);
> }
>
> -void __hyp_text __debug_switch_to_host(struct kvm_vcpu *vcpu)
> +void __hyp_text __debug_restore_host_context(struct kvm_vcpu *vcpu)

In the current state of the sources, __debug_switch_to_host() seems to
save the guest debug state before restoring the host's:

__debug_save_state(vcpu, guest_dbg, guest_ctxt);

Since you're splitting the switch_to into save/restore operations, it
feels like this would fit better __debug_save_guest_context() (currently
empty) rather than __debug_restore_host_context().

Cheers,

--
Julien Thierry