Re: [RFC PATCH 39/39] KVM: guest_memfd: Dynamically split/reconstruct HugeTLB page

On Tue, Sep 10, 2024 at 11:44:10PM +0000, Ackerley Tng wrote:

+/*

• • Allocates and then caches a folio in the filemap. Returns a folio with
• • refcount of 2: 1 after allocation, and 1 taken by the filemap.
• */

+static struct folio *kvm_gmem_hugetlb_alloc_and_cache_folio(struct inode *inode,

• 					    pgoff_t index)
  

+{

• struct kvm_gmem_hugetlb *hgmem;
• pgoff_t aligned_index;
• struct folio *folio;
• int nr_pages;
• int ret;
• hgmem = kvm_gmem_hgmem(inode);
• folio = kvm_gmem_hugetlb_alloc_folio(hgmem->h, hgmem->spool);
• if (IS_ERR(folio))

• return folio;
  

• nr_pages = 1UL << huge_page_order(hgmem->h);
• aligned_index = round_down(index, nr_pages);

Maybe a gap here.

When a guest_memfd is bound to a slot where slot->base_gfn is not aligned to 2M/1G and slot->gmem.pgoff is 0, even if an index is 2M/1G aligned, the corresponding GFN is not 2M/1G aligned.

However, TDX requires that private huge pages be 2M aligned in GFN.

• ret = kvm_gmem_hugetlb_filemap_add_folio(inode->i_mapping, folio,

• 				 aligned_index,
  

• 				 htlb_alloc_mask(hgmem->h));
  

• WARN_ON(ret);
• spin_lock(&inode->i_lock); inode->i_blocks += blocks_per_huge_page(hgmem->h); spin_unlock(&inode->i_lock);

• return page_folio(requested_page);

• return folio;

+}