From 17eed27b02da88560b4592390952b9a71042ab8b Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Tue, 31 Oct 2017 15:51:16 +0000 Subject: [PATCH] arm64/sve: KVM: Prevent guests from using SVE MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Until KVM has full SVE support, guests must not be allowed to execute SVE instructions. This patch enables the necessary traps, and also ensures that the traps are disabled again on exit from the guest so that the host can still use SVE if it wants to. On guest exit, high bits of the SVE Zn registers may have been clobbered as a side-effect the execution of FPSIMD instructions in the guest. The existing KVM host FPSIMD restore code is not sufficient to restore these bits, so this patch explicitly marks the CPU as not containing cached vector state for any task, thus forcing a reload on the next return to userspace. This is an interim measure, in advance of adding full SVE awareness to KVM. This marking of cached vector state in the CPU as invalid is done using __this_cpu_write(fpsimd_last_state, NULL) in fpsimd.c. Due to the repeated use of this rather obscure operation, it makes sense to factor it out as a separate helper with a clearer name. This patch factors it out as fpsimd_flush_cpu_state(), and ports all callers to use it. As a side effect of this refactoring, a this_cpu_write() in fpsimd_cpu_pm_notifier() is changed to __this_cpu_write(). This should be fine, since cpu_pm_enter() is supposed to be called only with interrupts disabled. Signed-off-by: Dave Martin Reviewed-by: Alex Bennée Reviewed-by: Christoffer Dall Acked-by: Catalin Marinas Acked-by: Marc Zyngier Cc: Ard Biesheuvel Signed-off-by: Will Deacon --- arch/arm/include/asm/kvm_host.h | 3 +++ arch/arm64/include/asm/fpsimd.h | 1 + arch/arm64/include/asm/kvm_arm.h | 4 +++- arch/arm64/include/asm/kvm_host.h | 11 +++++++++++ arch/arm64/kernel/fpsimd.c | 31 +++++++++++++++++++++++++++++-- arch/arm64/kvm/hyp/switch.c | 6 +++--- virt/kvm/arm/arm.c | 3 +++ 7 files changed, 53 insertions(+), 6 deletions(-) diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h index 4a879f6ff13b..242151ea6908 100644 --- a/arch/arm/include/asm/kvm_host.h +++ b/arch/arm/include/asm/kvm_host.h @@ -293,4 +293,7 @@ int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu, int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr); +/* All host FP/SIMD state is restored on guest exit, so nothing to save: */ +static inline void kvm_fpsimd_flush_cpu_state(void) {} + #endif /* __ARM_KVM_HOST_H__ */ diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h index b868412c815c..74f34392a531 100644 --- a/arch/arm64/include/asm/fpsimd.h +++ b/arch/arm64/include/asm/fpsimd.h @@ -74,6 +74,7 @@ extern void fpsimd_restore_current_state(void); extern void fpsimd_update_current_state(struct fpsimd_state *state); extern void fpsimd_flush_task_state(struct task_struct *target); +extern void sve_flush_cpu_state(void); /* Maximum VL that SVE VL-agnostic software can transparently support */ #define SVE_VL_ARCH_MAX 0x100 diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h index dbf05370169a..7f069ff37f06 100644 --- a/arch/arm64/include/asm/kvm_arm.h +++ b/arch/arm64/include/asm/kvm_arm.h @@ -186,7 +186,8 @@ #define CPTR_EL2_TTA (1 << 20) #define CPTR_EL2_TFP (1 << CPTR_EL2_TFP_SHIFT) #define CPTR_EL2_TZ (1 << 8) -#define CPTR_EL2_DEFAULT 0x000033ff +#define CPTR_EL2_RES1 0x000032ff /* known RES1 bits in CPTR_EL2 */ +#define CPTR_EL2_DEFAULT CPTR_EL2_RES1 /* Hyp Debug Configuration Register bits */ #define MDCR_EL2_TPMS (1 << 14) @@ -237,5 +238,6 @@ #define CPACR_EL1_FPEN (3 << 20) #define CPACR_EL1_TTA (1 << 28) +#define CPACR_EL1_DEFAULT (CPACR_EL1_FPEN | CPACR_EL1_ZEN_EL1EN) #endif /* __ARM64_KVM_ARM_H__ */ diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index e923b58606e2..674912d7a571 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -25,6 +25,7 @@ #include #include #include +#include #include #include #include @@ -384,4 +385,14 @@ static inline void __cpu_init_stage2(void) "PARange is %d bits, unsupported configuration!", parange); } +/* + * All host FP/SIMD state is restored on guest exit, so nothing needs + * doing here except in the SVE case: +*/ +static inline void kvm_fpsimd_flush_cpu_state(void) +{ + if (system_supports_sve()) + sve_flush_cpu_state(); +} + #endif /* __ARM64_KVM_HOST_H__ */ diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 88e5e6aef300..931fd8dca91a 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -1050,6 +1050,33 @@ void fpsimd_flush_task_state(struct task_struct *t) t->thread.fpsimd_state.cpu = NR_CPUS; } +static inline void fpsimd_flush_cpu_state(void) +{ + __this_cpu_write(fpsimd_last_state, NULL); +} + +/* + * Invalidate any task SVE state currently held in this CPU's regs. + * + * This is used to prevent the kernel from trying to reuse SVE register data + * that is detroyed by KVM guest enter/exit. This function should go away when + * KVM SVE support is implemented. Don't use it for anything else. + */ +#ifdef CONFIG_ARM64_SVE +void sve_flush_cpu_state(void) +{ + struct fpsimd_state *const fpstate = __this_cpu_read(fpsimd_last_state); + struct task_struct *tsk; + + if (!fpstate) + return; + + tsk = container_of(fpstate, struct task_struct, thread.fpsimd_state); + if (test_tsk_thread_flag(tsk, TIF_SVE)) + fpsimd_flush_cpu_state(); +} +#endif /* CONFIG_ARM64_SVE */ + #ifdef CONFIG_KERNEL_MODE_NEON DEFINE_PER_CPU(bool, kernel_neon_busy); @@ -1090,7 +1117,7 @@ void kernel_neon_begin(void) } /* Invalidate any task state remaining in the fpsimd regs: */ - __this_cpu_write(fpsimd_last_state, NULL); + fpsimd_flush_cpu_state(); preempt_disable(); @@ -1211,7 +1238,7 @@ static int fpsimd_cpu_pm_notifier(struct notifier_block *self, case CPU_PM_ENTER: if (current->mm) task_fpsimd_save(); - this_cpu_write(fpsimd_last_state, NULL); + fpsimd_flush_cpu_state(); break; case CPU_PM_EXIT: if (current->mm) diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c index 35a90b8be3da..951f3ebaff26 100644 --- a/arch/arm64/kvm/hyp/switch.c +++ b/arch/arm64/kvm/hyp/switch.c @@ -48,7 +48,7 @@ static void __hyp_text __activate_traps_vhe(void) val = read_sysreg(cpacr_el1); val |= CPACR_EL1_TTA; - val &= ~CPACR_EL1_FPEN; + val &= ~(CPACR_EL1_FPEN | CPACR_EL1_ZEN); write_sysreg(val, cpacr_el1); write_sysreg(__kvm_hyp_vector, vbar_el1); @@ -59,7 +59,7 @@ static void __hyp_text __activate_traps_nvhe(void) u64 val; val = CPTR_EL2_DEFAULT; - val |= CPTR_EL2_TTA | CPTR_EL2_TFP; + val |= CPTR_EL2_TTA | CPTR_EL2_TFP | CPTR_EL2_TZ; write_sysreg(val, cptr_el2); } @@ -117,7 +117,7 @@ static void __hyp_text __deactivate_traps_vhe(void) write_sysreg(mdcr_el2, mdcr_el2); write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2); - write_sysreg(CPACR_EL1_FPEN, cpacr_el1); + write_sysreg(CPACR_EL1_DEFAULT, cpacr_el1); write_sysreg(vectors, vbar_el1); } diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index b9f68e4add71..4d3cf9c82f5b 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -652,6 +652,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) */ preempt_disable(); + /* Flush FP/SIMD state that can't survive guest entry/exit */ + kvm_fpsimd_flush_cpu_state(); + kvm_pmu_flush_hwstate(vcpu); kvm_timer_flush_hwstate(vcpu); -- 2.30.2