On Tue, 17 Aug 2021 09:11:25 +0100,
Fuad Tabba <tabba@xxxxxxxxxx> wrote:
>
> On deactivating traps, restore the value of mdcr_el2 from the
> newly created and preserved host value vcpu context, rather than
> directly reading the hardware register.
>
> Up until and including this patch the two values are the same,
> i.e., the hardware register and the vcpu one. A future patch will
> be changing the value of mdcr_el2 on activating traps, and this
> ensures that its value will be restored.
>
> No functional change intended.
>
> Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/kvm_host.h | 5 ++++-
> arch/arm64/include/asm/kvm_hyp.h | 2 +-
> arch/arm64/kvm/hyp/include/hyp/switch.h | 6 +++++-
> arch/arm64/kvm/hyp/nvhe/switch.c | 13 +++++--------
> arch/arm64/kvm/hyp/vhe/switch.c | 14 +++++---------
> arch/arm64/kvm/hyp/vhe/sysreg-sr.c | 2 +-
> 6 files changed, 21 insertions(+), 21 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 4d2d974c1522..76462c6a91ee 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -287,10 +287,13 @@ struct kvm_vcpu_arch {
> /* Stage 2 paging state used by the hardware on next switch */
> struct kvm_s2_mmu *hw_mmu;
>
> - /* HYP configuration */
> + /* Values of trap registers for the guest. */
> u64 hcr_el2;
> u64 mdcr_el2;
>
> + /* Values of trap registers for the host before guest entry. */
> + u64 mdcr_el2_host;
This probably should then eventually replace the per-CPU copy of
mdcr_el2 that lives in debug.c, shouldn't it?
> +
> /* Exception Information */
> struct kvm_vcpu_fault_info fault;
>
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 9d60b3006efc..657d0c94cf82 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -95,7 +95,7 @@ void __sve_restore_state(void *sve_pffr, u32 *fpsr);
>
> #ifndef __KVM_NVHE_HYPERVISOR__
> void activate_traps_vhe_load(struct kvm_vcpu *vcpu);
> -void deactivate_traps_vhe_put(void);
> +void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu);
> #endif
>
> u64 __guest_enter(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index e4a2f295a394..a0e78a6027be 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -92,11 +92,15 @@ static inline void __activate_traps_common(struct kvm_vcpu *vcpu)
> write_sysreg(0, pmselr_el0);
> write_sysreg(ARMV8_PMU_USERENR_MASK, pmuserenr_el0);
> }
> +
> + vcpu->arch.mdcr_el2_host = read_sysreg(mdcr_el2);
> write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
> }
>
> -static inline void __deactivate_traps_common(void)
> +static inline void __deactivate_traps_common(struct kvm_vcpu *vcpu)
> {
> + write_sysreg(vcpu->arch.mdcr_el2_host, mdcr_el2);
> +
> write_sysreg(0, hstr_el2);
> if (kvm_arm_support_pmu_v3())
> write_sysreg(0, pmuserenr_el0);
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index f7af9688c1f7..2ea764a48958 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -69,12 +69,10 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
> static void __deactivate_traps(struct kvm_vcpu *vcpu)
> {
> extern char __kvm_hyp_host_vector[];
> - u64 mdcr_el2, cptr;
> + u64 cptr;
>
> ___deactivate_traps(vcpu);
>
> - mdcr_el2 = read_sysreg(mdcr_el2);
> -
> if (cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT)) {
> u64 val;
>
> @@ -92,13 +90,12 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
> isb();
> }
>
> - __deactivate_traps_common();
> + vcpu->arch.mdcr_el2_host &= MDCR_EL2_HPMN_MASK |
> + MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT |
> + MDCR_EL2_E2TB_MASK << MDCR_EL2_E2TB_SHIFT;
>
> - mdcr_el2 &= MDCR_EL2_HPMN_MASK;
> - mdcr_el2 |= MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT;
> - mdcr_el2 |= MDCR_EL2_E2TB_MASK << MDCR_EL2_E2TB_SHIFT;
> + __deactivate_traps_common(vcpu);
>
> - write_sysreg(mdcr_el2, mdcr_el2);
FWIW, I found this whole sequence massively confusing, and it is only
when I came to patch #7 that the various pieces did come together.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
