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Commit bd53cb35 authored by Filippo Sironi's avatar Filippo Sironi Committed by Paolo Bonzini
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X86/KVM: Handle PFNs outside of kernel reach when touching GPTEs 



cmpxchg_gpte() calls get_user_pages_fast() to retrieve the number of
pages and the respective struct page to map in the kernel virtual
address space.
This doesn't work if get_user_pages_fast() is invoked with a userspace
virtual address that's backed by PFNs outside of kernel reach (e.g., when
limiting the kernel memory with mem= in the command line and using
/dev/mem to map memory).

If get_user_pages_fast() fails, look up the VMA that back the userspace
virtual address, compute the PFN and the physical address, and map it in
the kernel virtual address space with memremap().

Signed-off-by: default avatarFilippo Sironi <sironi@amazon.de>
Signed-off-by: default avatarKarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 3d5f6beb

arch/x86/kvm/paging_tmpl.h

+29 −9
Original line number Diff line number Diff line
@@ -141,15 +141,35 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, 
	struct page *page;



	npages = get_user_pages_fast((unsigned long)ptep_user, 1, 1, &page);

	/* Check if the user is doing something meaningless. */

	if (unlikely(npages != 1))

		return -EFAULT;



	if (likely(npages == 1)) {

		table = kmap_atomic(page);

		ret = CMPXCHG(&table[index], orig_pte, new_pte);

		kunmap_atomic(table);



		kvm_release_page_dirty(page);

	} else {

		struct vm_area_struct *vma;

		unsigned long vaddr = (unsigned long)ptep_user & PAGE_MASK;

		unsigned long pfn;

		unsigned long paddr;



		down_read(&current->mm->mmap_sem);

		vma = find_vma_intersection(current->mm, vaddr, vaddr + PAGE_SIZE);

		if (!vma || !(vma->vm_flags & VM_PFNMAP)) {

			up_read(&current->mm->mmap_sem);

			return -EFAULT;

		}

		pfn = ((vaddr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

		paddr = pfn << PAGE_SHIFT;

		table = memremap(paddr, PAGE_SIZE, MEMREMAP_WB);

		if (!table) {

			up_read(&current->mm->mmap_sem);

			return -EFAULT;

		}

		ret = CMPXCHG(&table[index], orig_pte, new_pte);

		memunmap(table);

		up_read(&current->mm->mmap_sem);

	}



	return (ret != orig_pte);

}