Re: [PATCH v5] x86/devmem: Remove duplicate range_is_allowed() definition

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Apr 29, 2025 at 07:46:21PM -0700, Dan Williams wrote:
> 17 years ago, Venki suggested [1] "A future improvement would be to
> avoid the range_is_allowed duplication".
> 
> The only thing preventing a common implementation is that
> phys_mem_access_prot_allowed() expects the range check to exit
> immediately when PAT is disabled [2]. I.e. there is no cache conflict to
> manage in that case. This cleanup was noticed on the path to
> considering changing range_is_allowed() policy to blanket deny /dev/mem
> for private (confidential computing) memory.
> 
> Note, however that phys_mem_access_prot_allowed() has long since stopped
> being relevant for managing cache-type validation due to [3], and [4].
> 
> Commit 0124cecfc85a ("x86, PAT: disable /dev/mem mmap RAM with PAT") [1]
> Commit 9e41bff2708e ("x86: fix /dev/mem mmap breakage when PAT is disabled") [2]
> Commit 1886297ce0c8 ("x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386") [3]
> Commit 0c3c8a18361a ("x86, PAT: Remove duplicate memtype reserve in devmem mmap") [4]
> 
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: "Naveen N Rao" <naveen@kernel.org>
> Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  arch/x86/mm/pat/memtype.c | 31 ++++---------------------------
>  drivers/char/mem.c        | 18 ------------------
>  include/linux/io.h        | 21 +++++++++++++++++++++
>  3 files changed, 25 insertions(+), 45 deletions(-)


Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>