arm: KVM: Survive unknown traps from guests
Currently we BUG() if we see a HSR.EC value we don't recognise. As configurable disables/enables are added to the architecture (controlled by RES1/RES0 bits respectively), with associated synchronous exceptions, it may be possible for a guest to trigger exceptions with classes that we don't recognise. While we can't service these exceptions in a manner useful to the guest, we can avoid bringing down the host. Per ARM DDI 0406C.c, all currently unallocated HSR EC encodings are reserved, and per ARM DDI 0487A.k_iss10775, page G6-4395, EC values within the range 0x00 - 0x2c are reserved for future use with synchronous exceptions, and EC values within the range 0x2d - 0x3f may be used for either synchronous or asynchronous exceptions. The patch makes KVM handle any unknown EC by injecting an UNDEFINED exception into the guest, with a corresponding (ratelimited) warning in the host dmesg. We could later improve on this with with a new (opt-in) exit to the host userspace. Cc: Dave Martin <dave.martin@arm.com> Cc: Suzuki K Poulose <suzuki.poulose@arm.com> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org> Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
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@ -209,6 +209,7 @@
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#define HSR_EC_IABT_HYP (0x21)
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#define HSR_EC_DABT (0x24)
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#define HSR_EC_DABT_HYP (0x25)
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#define HSR_EC_MAX (0x3f)
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#define HSR_WFI_IS_WFE (_AC(1, UL) << 0)
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@ -79,7 +79,19 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
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return 1;
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}
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static int kvm_handle_unknown_ec(struct kvm_vcpu *vcpu, struct kvm_run *run)
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{
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u32 hsr = kvm_vcpu_get_hsr(vcpu);
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kvm_pr_unimpl("Unknown exception class: hsr: %#08x\n",
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hsr);
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kvm_inject_undefined(vcpu);
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return 1;
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}
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static exit_handle_fn arm_exit_handlers[] = {
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[0 ... HSR_EC_MAX] = kvm_handle_unknown_ec,
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[HSR_EC_WFI] = kvm_handle_wfx,
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[HSR_EC_CP15_32] = kvm_handle_cp15_32,
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[HSR_EC_CP15_64] = kvm_handle_cp15_64,
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@ -98,13 +110,6 @@ static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
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{
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u8 hsr_ec = kvm_vcpu_trap_get_class(vcpu);
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if (hsr_ec >= ARRAY_SIZE(arm_exit_handlers) ||
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!arm_exit_handlers[hsr_ec]) {
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kvm_err("Unknown exception class: hsr: %#08x\n",
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(unsigned int)kvm_vcpu_get_hsr(vcpu));
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BUG();
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}
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return arm_exit_handlers[hsr_ec];
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}
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