[bug report] KVM: x86/mmu: Use an rwlock for the x86 MMU

[Dan Carpenter <dan.carpenter@oracle.com>]

[ This is not the correct patch to blame, but there is something going
  on here which I don't understand so this email is more about me
  learning rather than reporting bugs. - dan ]

Hello Ben Gardon,

The patch 531810caa9f4: "KVM: x86/mmu: Use an rwlock for the x86 MMU"
from Feb 2, 2021, leads to the following static checker warning:

	arch/x86/kvm/mmu/mmu.c:5769 kvm_mmu_zap_all()
	warn: sleeping in atomic context

arch/x86/kvm/mmu/mmu.c
    5756 void kvm_mmu_zap_all(struct kvm *kvm)
    5757 {
    5758 	struct kvm_mmu_page *sp, *node;
    5759 	LIST_HEAD(invalid_list);
    5760 	int ign;
    5761 
    5762 	write_lock(&kvm->mmu_lock);
                ^^^^^^^^^^^^^^^^^^^^^^^^^^
This line bumps the preempt count.

    5763 restart:
    5764 	list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) {
    5765 		if (WARN_ON(sp->role.invalid))
    5766 			continue;
    5767 		if (__kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list, &ign))
    5768 			goto restart;
--> 5769 		if (cond_resched_rwlock_write(&kvm->mmu_lock))
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This line triggers a sleeping in atomic warning.  What's going on here
that I'm not understanding?

    5770 			goto restart;
    5771 	}
    5772 
    5773 	kvm_mmu_commit_zap_page(kvm, &invalid_list);
    5774 
    5775 	if (is_tdp_mmu_enabled(kvm))
    5776 		kvm_tdp_mmu_zap_all(kvm);
    5777 
    5778 	write_unlock(&kvm->mmu_lock);
    5779 }

regards,
dan carpenter