On Mon, Jun 08, 2020 at 09:56:57AM +0100, Marc Zyngier wrote:
> For very long, we have kept this pointer back to the per-cpu
> host state, despite having working per-cpu accessors at EL2
> for some time now.
>
> Recent investigations have shown that this pointer is easy
> to abuse in preemptible context, which is a sure sign that
> it would better be gone. Not to mention that a per-cpu
> pointer is faster to access at all times.
>
> Reported-by: Andrew Scull <asc...@google.com>
> Signed-off-by: Marc Zyngier <m...@kernel.org>
>From a quick scan, this looks sane to me, so FWIW:
Acked-by: Mark Rutland <mark.rutl...@arm.com>
Mark.
> ---
>
> Notes:
> v2: Stick to this_cpu_ptr() in pmu.c, as this only used on the
> kernel side and not the hypervisor.
>
> arch/arm64/include/asm/kvm_host.h | 3 ---
> arch/arm64/kvm/arm.c | 3 ---
> arch/arm64/kvm/hyp/debug-sr.c | 4 ++--
> arch/arm64/kvm/hyp/switch.c | 6 +++---
> arch/arm64/kvm/hyp/sysreg-sr.c | 6 ++++--
> arch/arm64/kvm/pmu.c | 8 ++------
> 6 files changed, 11 insertions(+), 19 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h
> b/arch/arm64/include/asm/kvm_host.h
> index 59029e90b557..ada1faa92211 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -284,9 +284,6 @@ struct kvm_vcpu_arch {
> struct kvm_guest_debug_arch vcpu_debug_state;
> struct kvm_guest_debug_arch external_debug_state;
>
> - /* Pointer to host CPU context */
> - struct kvm_cpu_context *host_cpu_context;
> -
> struct thread_info *host_thread_info; /* hyp VA */
> struct user_fpsimd_state *host_fpsimd_state; /* hyp VA */
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 14b747266607..6ddaa23ef346 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -340,10 +340,8 @@ void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
> void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> {
> int *last_ran;
> - kvm_host_data_t *cpu_data;
>
> last_ran = this_cpu_ptr(vcpu->kvm->arch.last_vcpu_ran);
> - cpu_data = this_cpu_ptr(&kvm_host_data);
>
> /*
> * We might get preempted before the vCPU actually runs, but
> @@ -355,7 +353,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> }
>
> vcpu->cpu = cpu;
> - vcpu->arch.host_cpu_context = &cpu_data->host_ctxt;
>
> kvm_vgic_load(vcpu);
> kvm_timer_vcpu_load(vcpu);
> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
> index 0fc9872a1467..e95af204fec7 100644
> --- a/arch/arm64/kvm/hyp/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/debug-sr.c
> @@ -185,7 +185,7 @@ void __hyp_text __debug_switch_to_guest(struct kvm_vcpu
> *vcpu)
> if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
> return;
>
> - host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> + host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
> guest_ctxt = &vcpu->arch.ctxt;
> host_dbg = &vcpu->arch.host_debug_state.regs;
> guest_dbg = kern_hyp_va(vcpu->arch.debug_ptr);
> @@ -207,7 +207,7 @@ void __hyp_text __debug_switch_to_host(struct kvm_vcpu
> *vcpu)
> if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
> return;
>
> - host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> + host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
> guest_ctxt = &vcpu->arch.ctxt;
> host_dbg = &vcpu->arch.host_debug_state.regs;
> guest_dbg = kern_hyp_va(vcpu->arch.debug_ptr);
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index fc09c3dfa466..fc671426c14b 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -544,7 +544,7 @@ static bool __hyp_text __hyp_handle_ptrauth(struct
> kvm_vcpu *vcpu)
> return false;
> }
>
> - ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> + ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
> __ptrauth_save_key(ctxt->sys_regs, APIA);
> __ptrauth_save_key(ctxt->sys_regs, APIB);
> __ptrauth_save_key(ctxt->sys_regs, APDA);
> @@ -715,7 +715,7 @@ static int __kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> struct kvm_cpu_context *guest_ctxt;
> u64 exit_code;
>
> - host_ctxt = vcpu->arch.host_cpu_context;
> + host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
> host_ctxt->__hyp_running_vcpu = vcpu;
> guest_ctxt = &vcpu->arch.ctxt;
>
> @@ -820,7 +820,7 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
>
> vcpu = kern_hyp_va(vcpu);
>
> - host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> + host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
> host_ctxt->__hyp_running_vcpu = vcpu;
> guest_ctxt = &vcpu->arch.ctxt;
>
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> index 6d2df9fe0b5d..143d7b7358f2 100644
> --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c
> @@ -265,12 +265,13 @@ void __hyp_text __sysreg32_restore_state(struct
> kvm_vcpu *vcpu)
> */
> void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu)
> {
> - struct kvm_cpu_context *host_ctxt = vcpu->arch.host_cpu_context;
> struct kvm_cpu_context *guest_ctxt = &vcpu->arch.ctxt;
> + struct kvm_cpu_context *host_ctxt;
>
> if (!has_vhe())
> return;
>
> + host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
> __sysreg_save_user_state(host_ctxt);
>
> /*
> @@ -301,12 +302,13 @@ void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu)
> */
> void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu)
> {
> - struct kvm_cpu_context *host_ctxt = vcpu->arch.host_cpu_context;
> struct kvm_cpu_context *guest_ctxt = &vcpu->arch.ctxt;
> + struct kvm_cpu_context *host_ctxt;
>
> if (!has_vhe())
> return;
>
> + host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
> deactivate_traps_vhe_put();
>
> __sysreg_save_el1_state(guest_ctxt);
> diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c
> index e71d00bb5271..b5ae3a5d509e 100644
> --- a/arch/arm64/kvm/pmu.c
> +++ b/arch/arm64/kvm/pmu.c
> @@ -163,15 +163,13 @@ static void kvm_vcpu_pmu_disable_el0(unsigned long
> events)
> */
> void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu)
> {
> - struct kvm_cpu_context *host_ctxt;
> struct kvm_host_data *host;
> u32 events_guest, events_host;
>
> if (!has_vhe())
> return;
>
> - host_ctxt = vcpu->arch.host_cpu_context;
> - host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
> + host = this_cpu_ptr(&kvm_host_data);
> events_guest = host->pmu_events.events_guest;
> events_host = host->pmu_events.events_host;
>
> @@ -184,15 +182,13 @@ void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu)
> */
> void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu)
> {
> - struct kvm_cpu_context *host_ctxt;
> struct kvm_host_data *host;
> u32 events_guest, events_host;
>
> if (!has_vhe())
> return;
>
> - host_ctxt = vcpu->arch.host_cpu_context;
> - host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
> + host = this_cpu_ptr(&kvm_host_data);
> events_guest = host->pmu_events.events_guest;
> events_host = host->pmu_events.events_host;
>
> --
> 2.26.2
>
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