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.
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index bd0727019674..e10962dfc203 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2238,7 +2238,7 @@ static bool kvm_mmu_remote_flush_or_zap(struct kvm *kvm,
> struct list_head *invalid_list,
> bool remote_flush)
> {
> - if (!remote_flush && !list_empty(invalid_list))
> + if (!remote_flush && list_empty(invalid_list))
> return false;
>
> if (!list_empty(invalid_list))
> --
> 2.21.0
>
