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From: | David Hildenbrand |
Subject: | Re: [PATCH] kvm: Fix crash by initializing kvm_state early |
Date: | Mon, 31 Jul 2023 09:18:09 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 |
On 31.07.23 01:48, Gavin Shan wrote:
Runs into core dump on arm64 and the backtrace extracted from the core dump is shown as below. It's caused by accessing @kvm_state which isn't initialized at that point due to commit 176d073029 ("hw/arm/virt: Use machine_memory_devices_init()"), where the machine's memory region is added ealier than before.
s/ealier/earlier/
main qemu_init configure_accelerators qemu_opts_foreach do_configure_accelerator accel_init_machine kvm_init virt_kvm_type virt_set_memmap machine_memory_devices_init memory_region_add_subregion memory_region_add_subregion_common memory_region_update_container_subregions memory_region_transaction_begin qemu_flush_coalesced_mmio_buffer kvm_flush_coalesced_mmio_buffer Fix it by initializing @kvm_state early. With this applied, no crash is observed on arm64.
Interestingly, we register memory listeners in kvm_init() after setting kvm_state, so in theory it should have worked fine.
But it's rather surprising that we see kvm_flush_coalesced_mmio_buffer() call even though we didn't even setup a listener with kvm_coalesce_mmio_region / kvm_uncoalesce_mmio_region.
Such a notifier-specific flush might have been better placed in the MemoryListener->begin() call. But that needs more thought, as qemu_flush_coalesced_mmio_buffer() is called from a couple of places.
Fixes: 176d073029 ("hw/arm/virt: Use machine_memory_devices_init()") Signed-off-by: Gavin Shan <gshan@redhat.com> --- accel/kvm/kvm-all.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index 373d876c05..c825cba12f 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -2464,6 +2464,7 @@ static int kvm_init(MachineState *ms) qemu_mutex_init(&kml_slots_lock);s = KVM_STATE(ms->accelerator);+ kvm_state = s;/** On systems where the kernel can support different base page @@ -2695,8 +2696,6 @@ static int kvm_init(MachineState *ms) #endif }- kvm_state = s;- ret = kvm_arch_init(ms, s); if (ret < 0) { goto err;
As an alternative, we might simply do nothing in kvm_flush_coalesced_mmio_buffer(), in case kvm_state is not setup yet. We don't have any notifier registered in that case.
Thanks! -- Cheers, David / dhildenb
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