Re: [PATCH 3/3] /dev/mem: Do not map unaccepted memory

[Kirill A. Shutemov]

On Wed, Sep 06, 2023 at 10:39:02AM +0300, Adrian Hunter wrote:
> Support for unaccepted memory was added recently, refer commit
> dcdfdd40fa82 ("mm: Add support for unaccepted memory"), whereby
> a virtual machine may need to accept memory before it can be used.
> 
> Do not map unaccepted memory because it can cause the guest to fail.
> 
> For /dev/mem, this means a read of unaccepted memory will return zeros,
> a write to unaccepted memory will be ignored, but an mmap of unaccepted
> memory will return an error.

I am unsure who currently uses /dev/mem. The change to the mmap path has the
potential to cause issues as it is a new behavior. However, it appears to
be a common practice as we also fail to mmap if PAT is set on a page in
the rang. I suppose it is acceptable.

Another option is to accept the memory on mmap, but it seems excessive at
this point.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov