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authorChristoffer Dall <christoffer.dall@arm.com>2019-10-11 13:07:05 +0200
committerMarc Zyngier <maz@kernel.org>2019-10-21 18:59:44 +0100
commitc726200dd106d4c58a281eea7159b8ba28a4ab34 (patch)
tree4fe3e68c19c2921fc108bae86e84f6cc331aac94 /virt
parent4f5cafb5cb8471e54afdc9054d973535614f7675 (diff)
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KVM: arm/arm64: Allow reporting non-ISV data aborts to userspace
For a long time, if a guest accessed memory outside of a memslot using any of the load/store instructions in the architecture which doesn't supply decoding information in the ESR_EL2 (the ISV bit is not set), the kernel would print the following message and terminate the VM as a result of returning -ENOSYS to userspace: load/store instruction decoding not implemented The reason behind this message is that KVM assumes that all accesses outside a memslot is an MMIO access which should be handled by userspace, and we originally expected to eventually implement some sort of decoding of load/store instructions where the ISV bit was not set. However, it turns out that many of the instructions which don't provide decoding information on abort are not safe to use for MMIO accesses, and the remaining few that would potentially make sense to use on MMIO accesses, such as those with register writeback, are not used in practice. It also turns out that fetching an instruction from guest memory can be a pretty horrible affair, involving stopping all CPUs on SMP systems, handling multiple corner cases of address translation in software, and more. It doesn't appear likely that we'll ever implement this in the kernel. What is much more common is that a user has misconfigured his/her guest and is actually not accessing an MMIO region, but just hitting some random hole in the IPA space. In this scenario, the error message above is almost misleading and has led to a great deal of confusion over the years. It is, nevertheless, ABI to userspace, and we therefore need to introduce a new capability that userspace explicitly enables to change behavior. This patch introduces KVM_CAP_ARM_NISV_TO_USER (NISV meaning Non-ISV) which does exactly that, and introduces a new exit reason to report the event to userspace. User space can then emulate an exception to the guest, restart the guest, suspend the guest, or take any other appropriate action as per the policy of the running system. Reported-by: Heinrich Schuchardt <xypron.glpk@gmx.de> Signed-off-by: Christoffer Dall <christoffer.dall@arm.com> Reviewed-by: Alexander Graf <graf@amazon.com> Signed-off-by: Marc Zyngier <maz@kernel.org>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/arm/arm.c21
-rw-r--r--virt/kvm/arm/mmio.c9
2 files changed, 29 insertions, 1 deletions
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 86c6aa1cb58e..e6d56f60e4b6 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -98,6 +98,26 @@ int kvm_arch_check_processor_compat(void)
return 0;
}
+int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
+ struct kvm_enable_cap *cap)
+{
+ int r;
+
+ if (cap->flags)
+ return -EINVAL;
+
+ switch (cap->cap) {
+ case KVM_CAP_ARM_NISV_TO_USER:
+ r = 0;
+ kvm->arch.return_nisv_io_abort_to_user = true;
+ break;
+ default:
+ r = -EINVAL;
+ break;
+ }
+
+ return r;
+}
/**
* kvm_arch_init_vm - initializes a VM data structure
@@ -197,6 +217,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_IMMEDIATE_EXIT:
case KVM_CAP_VCPU_EVENTS:
case KVM_CAP_ARM_IRQ_LINE_LAYOUT_2:
+ case KVM_CAP_ARM_NISV_TO_USER:
r = 1;
break;
case KVM_CAP_ARM_SET_DEVICE_ADDR:
diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
index 6af5c91337f2..70d3b449692c 100644
--- a/virt/kvm/arm/mmio.c
+++ b/virt/kvm/arm/mmio.c
@@ -167,7 +167,14 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
if (ret)
return ret;
} else {
- kvm_err("load/store instruction decoding not implemented\n");
+ if (vcpu->kvm->arch.return_nisv_io_abort_to_user) {
+ run->exit_reason = KVM_EXIT_ARM_NISV;
+ run->arm_nisv.esr_iss = kvm_vcpu_dabt_iss_nisv_sanitized(vcpu);
+ run->arm_nisv.fault_ipa = fault_ipa;
+ return 0;
+ }
+
+ kvm_pr_unimpl("Data abort outside memslots with no valid syndrome info\n");
return -ENOSYS;
}