On 9/5/19 10:03 AM, Marc Zyngier wrote:
[Please use my kernel.org address. My arm.com address will disappear shortly] On Wed, 04 Sep 2019 19:07:36 +0100, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote:If an application tries to access memory that is not mapped, an error ENOSYS, "load/store instruction decoding not implemented" may occur. QEMU will hang with a register dump. Instead create a data abort that can be handled gracefully by the application running in the virtual environment. Now the virtual machine can react to the event in the most appropriate way - by recovering, by writing an informative log, or by rebooting. Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx> --- virt/kvm/arm/mmio.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c index a8a6a0c883f1..0cbed7d6a0f4 100644 --- a/virt/kvm/arm/mmio.c +++ b/virt/kvm/arm/mmio.c @@ -161,8 +161,8 @@ 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"); - return -ENOSYS; + kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu)); + return 1;How can you tell that the access would fault? You have no idea at that stage (the kernel doesn't know about the MMIO ranges that userspace handles). All you know is that you're faced with a memory access that you cannot emulate in the kernel. Injecting a data abort at that stage is not something that the architecture allows. If you want to address this, consider forwarding the access to userspace. You'll only need an instruction decoder (supporting T1, T2, A32 and A64) and a S1 page table walker (one per page table format, all three of them) to emulate the access (having taken care of stopping all the other vcpus to make sure there is no concurrent modification of the page tables). You'll then be able to return the result of the access back to the kernel.
If I understand you right, the problem has to be fixed in QEMU and not in KVM. Is there an example of such a forwarding already available in QEMU?
Of course, the best thing would be to actually fix the guest so that it doesn't use non-emulatable MMIO accesses. In general, that the sign of a bug in low-level accessors.
My problem was to find out where in my guest (U-Boot running UEFI SCT) the problem occurred. With this patch U-Boot gave me the relative address in Shell.efi and I was able to locate what was wrong in U-Boot's UEFI implementation. Thanks for reviewing. Heinrich _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
