On Fri, Mar 14, 2025 at 05:20:21PM +0800, Yan Zhao wrote:
> This patch would cause host deadlock when booting up a TDX VM even if huge page
> is turned off. I currently reverted this patch. No further debug yet.
This is because kvm_gmem_populate() takes filemap invalidation lock, and for
TDX, kvm_gmem_populate() further invokes kvm_gmem_get_pfn(), causing deadlock.
kvm_gmem_populate
filemap_invalidate_lock
post_populate
tdx_gmem_post_populate
kvm_tdp_map_page
kvm_mmu_do_page_fault
kvm_tdp_page_fault
kvm_tdp_mmu_page_fault
kvm_mmu_faultin_pfn
__kvm_mmu_faultin_pfn
kvm_mmu_faultin_pfn_private
kvm_gmem_get_pfn
filemap_invalidate_lock_shared
Though, kvm_gmem_populate() is able to take shared filemap invalidation lock,
(then no deadlock), lockdep would still warn "Possible unsafe locking scenario:
...DEADLOCK" due to the recursive shared lock, since commit e918188611f0
("locking: More accurate annotations for read_lock()").
> > @@ -819,12 +827,16 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> > pgoff_t index = kvm_gmem_get_index(slot, gfn);
> > struct file *file = kvm_gmem_get_file(slot);
> > int max_order_local;
> > + struct address_space *mapping;
> > struct folio *folio;
> > int r = 0;
> >
> > if (!file)
> > return -EFAULT;
> >
> > + mapping = file->f_inode->i_mapping;
> > + filemap_invalidate_lock_shared(mapping);
> > +
> > /*
> > * The caller might pass a NULL 'max_order', but internally this
> > * function needs to be aware of any order limitations set by
> > @@ -838,6 +850,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> > folio = __kvm_gmem_get_pfn(file, slot, index, pfn, &max_order_local);
> > if (IS_ERR(folio)) {
> > r = PTR_ERR(folio);
> > + filemap_invalidate_unlock_shared(mapping);
> > goto out;
> > }
> >
> > @@ -845,6 +858,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> > r = kvm_gmem_prepare_folio(kvm, file, slot, gfn, folio, max_order_local);
> >
> > folio_unlock(folio);
> > + filemap_invalidate_unlock_shared(mapping);
> >
> > if (!r)
> > *page = folio_file_page(folio, index);
> > --
> > 2.25.1
> >
> >
