Re: [PATCH v2 08/18] arm64: KVM: add support to save/restore SPE profiling buffer controls

Marc Zyngier
2019-12-21T13:58:01Z

On Fri, 20 Dec 2019 14:30:15 +0000
Andrew Murray <andrew.murray@arm.com> wrote:

> From: Sudeep Holla <sudeep.holla@arm.com>
>
> Currently since we don't support profiling using SPE in the guests,
> we just save the PMSCR_EL1, flush the profiling buffers and disable
> sampling. However in order to support simultaneous sampling both in

Is the sampling actually simultaneous? I don't believe so (the whole
series would be much simpler if it was).

> the host and guests, we need to save and reatore the complete SPE

s/reatore/restore/

> profiling buffer controls' context.
>
> Let's add the support for the same and keep it disabled for now.
> We can enable it conditionally only if guests are allowed to use
> SPE.
>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> [ Clear PMBSR bit when saving state to prevent spurious interrupts ]
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
> arch/arm64/kvm/hyp/debug-sr.c | 51 +++++++++++++++++++++++++++++------
> 1 file changed, 43 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
> index 8a70a493345e..12429b212a3a 100644
> --- a/arch/arm64/kvm/hyp/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/debug-sr.c
> @@ -85,7 +85,8 @@
> default: write_debug(ptr[0], reg, 0); \
> }
>
> -static void __hyp_text __debug_save_spe_nvhe(struct kvm_cpu_context *ctxt)
> +static void __hyp_text
> +__debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt)

nit: don't split lines like this if you can avoid it. You can put the
full_ctxt parameter on a separate line instead.

> {
> u64 reg;
>
> @@ -102,22 +103,46 @@ static void __hyp_text __debug_save_spe_nvhe(struct kvm_cpu_context *ctxt)
> if (reg & BIT(SYS_PMBIDR_EL1_P_SHIFT))
> return;
>
> - /* No; is the host actually using the thing? */
> - reg = read_sysreg_s(SYS_PMBLIMITR_EL1);
> - if (!(reg & BIT(SYS_PMBLIMITR_EL1_E_SHIFT)))
> + /* Save the control register and disable data generation */
> + ctxt->sys_regs[PMSCR_EL1] = read_sysreg_el1(SYS_PMSCR);
> +
> + if (!ctxt->sys_regs[PMSCR_EL1])

Shouldn't you check the enable bits instead of relying on the whole
thing being zero?

> return;
>
> /* Yes; save the control register and disable data generation */
> - ctxt->sys_regs[PMSCR_EL1] = read_sysreg_el1(SYS_PMSCR);

You've already saved the control register...

> write_sysreg_el1(0, SYS_PMSCR);
> isb();
>
> /* Now drain all buffered data to memory */
> psb_csync();
> dsb(nsh);
> +
> + if (!full_ctxt)
> + return;
> +
> + ctxt->sys_regs[PMBLIMITR_EL1] = read_sysreg_s(SYS_PMBLIMITR_EL1);
> + write_sysreg_s(0, SYS_PMBLIMITR_EL1);
> +
> + /*
> + * As PMBSR is conditionally restored when returning to the host we
> + * must ensure the service bit is unset here to prevent a spurious
> + * host SPE interrupt from being raised.
> + */
> + ctxt->sys_regs[PMBSR_EL1] = read_sysreg_s(SYS_PMBSR_EL1);
> + write_sysreg_s(0, SYS_PMBSR_EL1);
> +
> + isb();
> +
> + ctxt->sys_regs[PMSICR_EL1] = read_sysreg_s(SYS_PMSICR_EL1);
> + ctxt->sys_regs[PMSIRR_EL1] = read_sysreg_s(SYS_PMSIRR_EL1);
> + ctxt->sys_regs[PMSFCR_EL1] = read_sysreg_s(SYS_PMSFCR_EL1);
> + ctxt->sys_regs[PMSEVFR_EL1] = read_sysreg_s(SYS_PMSEVFR_EL1);
> + ctxt->sys_regs[PMSLATFR_EL1] = read_sysreg_s(SYS_PMSLATFR_EL1);
> + ctxt->sys_regs[PMBPTR_EL1] = read_sysreg_s(SYS_PMBPTR_EL1);
> }
>
> -static void __hyp_text __debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt)
> +static void __hyp_text
> +__debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt)
> {
> if (!ctxt->sys_regs[PMSCR_EL1])
> return;
> @@ -126,6 +151,16 @@ static void __hyp_text __debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt)
> isb();
>
> /* Re-enable data generation */
> + if (full_ctxt) {
> + write_sysreg_s(ctxt->sys_regs[PMBPTR_EL1], SYS_PMBPTR_EL1);
> + write_sysreg_s(ctxt->sys_regs[PMBLIMITR_EL1], SYS_PMBLIMITR_EL1);
> + write_sysreg_s(ctxt->sys_regs[PMSFCR_EL1], SYS_PMSFCR_EL1);
> + write_sysreg_s(ctxt->sys_regs[PMSEVFR_EL1], SYS_PMSEVFR_EL1);
> + write_sysreg_s(ctxt->sys_regs[PMSLATFR_EL1], SYS_PMSLATFR_EL1);
> + write_sysreg_s(ctxt->sys_regs[PMSIRR_EL1], SYS_PMSIRR_EL1);
> + write_sysreg_s(ctxt->sys_regs[PMSICR_EL1], SYS_PMSICR_EL1);
> + write_sysreg_s(ctxt->sys_regs[PMBSR_EL1], SYS_PMBSR_EL1);
> + }
> write_sysreg_el1(ctxt->sys_regs[PMSCR_EL1], SYS_PMSCR);
> }
>
> @@ -198,7 +233,7 @@ void __hyp_text __debug_restore_host_context(struct kvm_vcpu *vcpu)
> guest_ctxt = &vcpu->arch.ctxt;
>
> if (!has_vhe())
> - __debug_restore_spe_nvhe(host_ctxt);
> + __debug_restore_spe_nvhe(host_ctxt, false);
>
> if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
> return;
> @@ -222,7 +257,7 @@ void __hyp_text __debug_save_host_context(struct kvm_vcpu *vcpu)
>
> host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> if (!has_vhe())
> - __debug_save_spe_nvhe(host_ctxt);
> + __debug_save_spe_nvhe(host_ctxt, false);
> }
>
> void __hyp_text __debug_save_guest_context(struct kvm_vcpu *vcpu)

So all of this is for non-VHE. What happens in the VHE case?

M.
--
Jazz is not dead. It just smells funny...