On Wed, Jan 09, 2019 at 10:42:03AM +0100, KarimAllah Ahmed wrote:
> From: Filippo Sironi
>
> 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: Filippo Sironi
> Signed-off-by: KarimAllah Ahmed
I personally would have used some crafty goto statements to jump to
'err' label which would have
up_read(>mm->mmap_sem);
return -EFAULT;
which would be after
154 return (ret != orig_pte);
But that is bike-shedding so feel free to ignore it.
Either way:
Reviewed-by: Konrad Rzeszutek Wilk
> ---
> arch/x86/kvm/paging_tmpl.h | 38 +-
> 1 file changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 6bdca39..c40af67 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -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, );
> - /* Check if the user is doing something meaningless. */
> - if (unlikely(npages != 1))
> - return -EFAULT;
> -
> - table = kmap_atomic(page);
> - ret = CMPXCHG([index], orig_pte, new_pte);
> - kunmap_atomic(table);
> -
> - kvm_release_page_dirty(page);
> + if (likely(npages == 1)) {
> + table = kmap_atomic(page);
> + ret = CMPXCHG([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(>mm->mmap_sem);
> + vma = find_vma_intersection(current->mm, vaddr, vaddr +
> PAGE_SIZE);
> + if (!vma || !(vma->vm_flags & VM_PFNMAP)) {
> + up_read(>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(>mm->mmap_sem);
> + return -EFAULT;
> + }
> + ret = CMPXCHG([index], orig_pte, new_pte);
> + memunmap(table);
> + up_read(>mm->mmap_sem);
> + }
>
> return (ret != orig_pte);
> }
> --
> 2.7.4
>
