Re: [PATCH 0/6] KVM: Remove uses of struct page from x86 and arm64 MMU

On 24/06/21 13:42, Nicholas Piggin wrote:

+static int kvm_try_get_pfn(kvm_pfn_t pfn) +{

• if (kvm_is_reserved_pfn(pfn))

• return 1;
  

So !pfn_valid would always return true. Yeah, this should work and is certainly appealing!

Paolo

• return get_page_unless_zero(pfn_to_page(pfn));

+}

• static int hva_to_pfn_remapped(struct vm_area_struct *vma, unsigned long addr, bool *async, bool write_fault, bool *writable,

@@ -2104,13 +2111,21 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, * Whoever called remap_pfn_range is also going to call e.g. * unmap_mapping_range before the underlying pages are freed, * causing a call to our MMU notifier.

• *
  

• * Certain IO or PFNMAP mappings can be backed with valid
  

• * struct pages, but be allocated without refcounting e.g.,
  

• * tail pages of non-compound higher order allocations, which
  

• * would then underflow the refcount when the caller does the
  

• * required put_page. Don't allow those pages here.
  

  */

• kvm_get_pfn(pfn);

• if (!kvm_try_get_pfn(pfn))

• r = -EFAULT;
  
  

  out: pte_unmap_unlock(ptep, ptl); *p_pfn = pfn;

• return 0;

• return r; }

  /*