Re: [PATCH v2 9/9] arm64: KVM: enable trapping of all debug registers

Christoffer Dall
2014-05-25T15:36:34Z

On Tue, May 20, 2014 at 05:55:45PM +0100, Marc Zyngier wrote:
> Enable trapping of the debug registers, preventing the guests to
> mess with the host state (and allowing guests to use the debug
> infrastructure as well).
>
> Reviewed-by: Anup Patel <anup.patel@linaro.org>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm64/kvm/hyp.S | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index 73ec5c4..72ed0bf8 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S
> @@ -777,6 +777,14 @@ __kvm_hyp_code_start:
> mrs x2, mdcr_el2
> and x2, x2, #MDCR_EL2_HPMN_MASK
> orr x2, x2, #(MDCR_EL2_TPM | MDCR_EL2_TPMCR)
> + orr x2, x2, #(MDCR_EL2_TDRA | MDCR_EL2_TDOSA)

so we unconditionally trap on the OS register access, but we don't
properly emulate these do we? What's the rationale? (atmittedly,
again, I'm not 100% clear on how the OS lock thingy is supposed to
work/be used).

> +
> + // Check for KVM_ARM64_DEBUG_DIRTY, and set to debug to trap
> + // if not dirty.

s/set to debug to trap/set debug to trap/ ??

> + ldr x3, [x0, #VCPU_DEBUG_FLAGS]
> + tbnz x3, #KVM_ARM64_DEBUG_DIRTY_SHIFT, 1f
> + orr x2, x2, #MDCR_EL2_TDA
> +1:
> msr mdcr_el2, x2
> .endm
>
> --
> 1.8.3.4
>

as per the functionality in this patch otherwise:

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>