On 15/04/19 16:44, Sean Christopherson wrote:
> On Fri, Apr 12, 2019 at 07:55:41PM -0700, Sean Christopherson wrote:
>> A recently introduced helper for handling zap vs. remote flush
>> incorrectly bails early, effectively leaking defunct shadow pages.
>> Manifests as a slab BUG when exiting KVM due to the shadow pages
>> being alive when their associated cache is destroyed.
>>
>> ==========================================================================
>> BUG kvm_mmu_page_header: Objects remaining in kvm_mmu_page_header on ...
>> --------------------------------------------------------------------------
>> Disabling lock debugging due to kernel taint
>> INFO: Slab 0x00000000fc436387 objects=26 used=23 fp=0x00000000d023caee ...
>> CPU: 6 PID: 4315 Comm: rmmod Tainted: G B 5.1.0-rc2+ #19
>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
>> Call Trace:
>> dump_stack+0x46/0x5b
>> slab_err+0xad/0xd0
>> ? on_each_cpu_mask+0x3c/0x50
>> ? ksm_migrate_page+0x60/0x60
>> ? on_each_cpu_cond_mask+0x7c/0xa0
>> ? __kmalloc+0x1ca/0x1e0
>> __kmem_cache_shutdown+0x13a/0x310
>> shutdown_cache+0xf/0x130
>> kmem_cache_destroy+0x1d5/0x200
>> kvm_mmu_module_exit+0xa/0x30 [kvm]
>> kvm_arch_exit+0x45/0x60 [kvm]
>> kvm_exit+0x6f/0x80 [kvm]
>> vmx_exit+0x1a/0x50 [kvm_intel]
>> __x64_sys_delete_module+0x153/0x1f0
>> ? exit_to_usermode_loop+0x88/0xc0
>> do_syscall_64+0x4f/0x100
>> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>
>> Fixes: a21136345cb6f ("KVM: x86/mmu: Split remote_flush+zap case out of kvm_mmu_flush_or_zap()")
>> Cc: stable@xxxxxxxxxxxxxxx
>
> Stable doesn't need to be Cc'd. I got my kernel versions mixed up, this
> bug only exists in 5.1.
Indeed, I've already tested this and it seems to work fine (despite
being a prime candidate for hiding other worse bugs :)).
I will send the pull request to Linus either today or tomorrow.
Paolo
