Re: [PATCH v8 5/9] KVM: arm/arm64: preserve host MDCR_EL2 value

From: Dave Martin
Date: Fri Apr 05 2019 - 07:02:44 EST

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In reply to: Amit Daniel Kachhap: "[PATCH v8 5/9] KVM: arm/arm64: preserve host MDCR_EL2 value"
Next in thread: Amit Daniel Kachhap: "[PATCH v8 7/9] KVM: arm/arm64: context-switch ptrauth registers"
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On Tue, Apr 02, 2019 at 07:57:13AM +0530, Amit Daniel Kachhap wrote:
> Save host MDCR_EL2 value during kvm HYP initialisation and restore
> after every switch from host to guest. There should not be any
> change in functionality due to this.
>
> The value of mdcr_el2 is now stored in struct kvm_cpu_context as
> both host and guest can now use this field in a common way.
>
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
> Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx
> ---
>
> Changes since v7:
> * Removed unused function __kvm_get_mdcr_el2 [Kristina].
>
> arch/arm/include/asm/kvm_host.h | 1 -
> arch/arm64/include/asm/kvm_asm.h | 2 --
> arch/arm64/include/asm/kvm_host.h | 6 ++----
> arch/arm64/include/asm/kvm_hyp.h | 2 +-
> arch/arm64/kvm/debug.c | 28 ++++++----------------------
> arch/arm64/kvm/hyp/debug-sr.c | 5 -----
> arch/arm64/kvm/hyp/switch.c | 18 +++++-------------
> arch/arm64/kvm/hyp/sysreg-sr.c | 8 +++++++-
> virt/kvm/arm/arm.c | 1 -
> 9 files changed, 21 insertions(+), 50 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 6d0aac4..a928565 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -343,7 +343,6 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
>
> -static inline void kvm_arm_init_debug(void) {}
> static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {}
> static inline void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) {}
> static inline void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu) {}
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index a68205c..a15ba55 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -78,8 +78,6 @@ extern u64 __vgic_v3_read_vmcr(void);
> extern void __vgic_v3_write_vmcr(u32 vmcr);
> extern void __vgic_v3_init_lrs(void);
>
> -extern u32 __kvm_get_mdcr_el2(void);
> -
> extern void __kvm_populate_host_regs(void);
>
> /*
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 3b09fd0..e3ccd7b 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -211,6 +211,8 @@ struct kvm_cpu_context {
>
> /* HYP host/guest configuration */
> u64 hcr_el2;
> + u32 mdcr_el2;
> +
> struct kvm_vcpu *__hyp_running_vcpu;
> };
>
> @@ -226,9 +228,6 @@ struct vcpu_reset_state {
> struct kvm_vcpu_arch {
> struct kvm_cpu_context ctxt;
>
> - /* HYP configuration */
> - u32 mdcr_el2;
> -
> /* Exception Information */
> struct kvm_vcpu_fault_info fault;
>
> @@ -498,7 +497,6 @@ static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
> static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
>
> -void kvm_arm_init_debug(void);
> void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
> void kvm_arm_clear_debug(struct kvm_vcpu *vcpu);
> void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 4da765f..7fcde8a 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -152,7 +152,7 @@ void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
> bool __fpsimd_enabled(void);
>
> void activate_traps_vhe_load(struct kvm_vcpu *vcpu);
> -void deactivate_traps_vhe_put(void);
> +void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu);
>
> u64 __guest_enter(struct kvm_vcpu *vcpu, struct kvm_cpu_context *host_ctxt);
> void __noreturn __hyp_do_panic(unsigned long, ...);
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index fd917d6..99dc0a4 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -32,8 +32,6 @@
> DBG_MDSCR_KDE | \
> DBG_MDSCR_MDE)
>
> -static DEFINE_PER_CPU(u32, mdcr_el2);
> -
> /**
> * save/restore_guest_debug_regs
> *
> @@ -65,21 +63,6 @@ static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
> }
>
> /**
> - * kvm_arm_init_debug - grab what we need for debug
> - *
> - * Currently the sole task of this function is to retrieve the initial
> - * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
> - * presumably been set-up by some knowledgeable bootcode.
> - *
> - * It is called once per-cpu during CPU hyp initialisation.
> - */
> -
> -void kvm_arm_init_debug(void)
> -{
> - __this_cpu_write(mdcr_el2, kvm_call_hyp_ret(__kvm_get_mdcr_el2));
> -}
> -
> -/**
> * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
> */
>
> @@ -111,6 +94,7 @@ void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
>
> void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
> {
> + kvm_cpu_context_t *host_cxt = this_cpu_ptr(&kvm_host_cpu_state);
> bool trap_debug = !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY);
> unsigned long mdscr;
>
> @@ -120,8 +104,8 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
> * This also clears MDCR_EL2_E2PB_MASK to disable guest access
> * to the profiling buffer.
> */
> - vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
> - vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
> + vcpu->arch.ctxt.mdcr_el2 = host_cxt->mdcr_el2 & MDCR_EL2_HPMN_MASK;
> + vcpu->arch.ctxt.mdcr_el2 |= (MDCR_EL2_TPM |
> MDCR_EL2_TPMS |
> MDCR_EL2_TPMCR |
> MDCR_EL2_TDRA |
> @@ -130,7 +114,7 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
> /* Is Guest debugging in effect? */
> if (vcpu->guest_debug) {
> /* Route all software debug exceptions to EL2 */
> - vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
> + vcpu->arch.ctxt.mdcr_el2 |= MDCR_EL2_TDE;
>
> /* Save guest debug state */
> save_guest_debug_regs(vcpu);
> @@ -202,13 +186,13 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
>
> /* Trap debug register access */
> if (trap_debug)
> - vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
> + vcpu->arch.ctxt.mdcr_el2 |= MDCR_EL2_TDA;
>
> /* If KDE or MDE are set, perform a full save/restore cycle. */
> if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
> vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
>
> - trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
> + trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.ctxt.mdcr_el2);
> trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
> }
>
> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
> index 5000976..f49a3f7 100644
> --- a/arch/arm64/kvm/hyp/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/debug-sr.c
> @@ -198,8 +198,3 @@ void __hyp_text __debug_switch_to_host(struct kvm_vcpu *vcpu)
>
> vcpu->arch.flags &= ~KVM_ARM64_DEBUG_DIRTY;
> }
> -
> -u32 __hyp_text __kvm_get_mdcr_el2(void)
> -{
> - return read_sysreg(mdcr_el2);
> -}
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index f5cefa1..fe76e24 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -84,7 +84,7 @@ static void __hyp_text __activate_traps_common(struct kvm_vcpu *vcpu)
> */
> write_sysreg(0, pmselr_el0);
> write_sysreg(ARMV8_PMU_USERENR_MASK, pmuserenr_el0);
> - write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
> + write_sysreg(vcpu->arch.ctxt.mdcr_el2, mdcr_el2);
> }
>
> static void __hyp_text __deactivate_traps_common(void)
> @@ -161,15 +161,11 @@ NOKPROBE_SYMBOL(deactivate_traps_vhe);
>
> static void __hyp_text __deactivate_traps_nvhe(struct kvm_cpu_context *host_ctxt)
> {
> - u64 mdcr_el2 = read_sysreg(mdcr_el2);
> struct kvm_cpu_context *hyp_host_ctxt = kern_hyp_va(host_ctxt);
>
> __deactivate_traps_common();
>
> - mdcr_el2 &= MDCR_EL2_HPMN_MASK;
> - mdcr_el2 |= MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT;
> -
> - write_sysreg(mdcr_el2, mdcr_el2);
> + write_sysreg(hyp_host_ctxt->mdcr_el2, mdcr_el2);
> write_sysreg(hyp_host_ctxt->hcr_el2, hcr_el2);
> write_sysreg(CPTR_EL2_DEFAULT, cptr_el2);
> }
> @@ -199,15 +195,11 @@ void activate_traps_vhe_load(struct kvm_vcpu *vcpu)
> __activate_traps_common(vcpu);
> }
>
> -void deactivate_traps_vhe_put(void)
> +void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu)
> {
> - u64 mdcr_el2 = read_sysreg(mdcr_el2);
> -
> - mdcr_el2 &= MDCR_EL2_HPMN_MASK |
> - MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT |
> - MDCR_EL2_TPMS;
> + struct kvm_cpu_context *host_ctxt = vcpu->arch.host_cpu_context;
>
> - write_sysreg(mdcr_el2, mdcr_el2);
> + write_sysreg(host_ctxt->mdcr_el2, mdcr_el2);
>
> __deactivate_traps_common();
> }
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> index 277f82b..6afd309 100644
> --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> @@ -298,7 +298,7 @@ void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu)
> if (!has_vhe())
> return;
>
> - deactivate_traps_vhe_put();
> + deactivate_traps_vhe_put(vcpu);
>
> __sysreg_save_el1_state(guest_ctxt);
> __sysreg_save_user_state(guest_ctxt);
> @@ -333,4 +333,10 @@ void __hyp_text __kvm_populate_host_regs(void)
>
> host_ctxt = __hyp_this_cpu_ptr(kvm_host_cpu_state);
> host_ctxt->hcr_el2 = read_sysreg(hcr_el2);
> + /*
> + * Retrieve the initial value of mdcr_el2 so we can preserve
> + * MDCR_EL2.HPMN which has presumably been set-up by some
> + * knowledgeable bootcode.
> + */
> + host_ctxt->mdcr_el2 = read_sysreg(mdcr_el2);
> }
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index e8c2ee6..58de0ca 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -1322,7 +1322,6 @@ static void cpu_hyp_reinit(void)
> else
> cpu_init_hyp_mode(NULL);
>
> - kvm_arm_init_debug();
> cpu_init_host_ctxt();
>
> if (vgic_present)

Looks reasonable overall.

I was wondering whether it would make sense to move some masking into
__kvm_populate_host_regs(), but probably not.

Reviewed-by: Dave Martin <Dave.Martin@xxxxxxx>

Cheers
---Dave

> --
> 2.7.4
>
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> kvmarm@xxxxxxxxxxxxxxxxxxxxx
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Next message: Dave Martin: "Re: [PATCH v8 6/9] KVM: arm64: Add vcpu feature flags to control ptrauth accessibility"
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In reply to: Amit Daniel Kachhap: "[PATCH v8 5/9] KVM: arm/arm64: preserve host MDCR_EL2 value"
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