[RFC PATCH v2 08/11] ARM64: mm: Swap PTE_FILE and PTE_PROT_NONE bits.
From: catalin.marinas@arm.com (Catalin Marinas)
Date: 2013-05-16 14:59:04
Also in:
linux-arch, linux-mm
On Wed, May 08, 2013 at 10:52:40AM +0100, Steve Capper wrote:
Under ARM64, PTEs can be broadly categorised as follows:
- Present and valid: Bit #0 is set. The PTE is valid and memory
access to the region may fault.
- Present and invalid: Bit #0 is clear and bit #1 is set.
Represents present memory with PROT_NONE protection. The PTE
is an invalid entry, and the user fault handler will raise a
SIGSEGV.
- Not present (file): Bits #0 and #1 are clear, bit #2 is set.
Memory represented has been paged out. The PTE is an invalid
entry, and the fault handler will try and re-populate the
memory where necessary.
Huge PTEs are block descriptors that have bit #1 clear. If we wish
to represent PROT_NONE huge PTEs we then run into a problem as
there is no way to distinguish between regular and huge PTEs if we
set bit #1.
As huge PTEs are always present, the meaning of bits #1 and #2 can
be swapped for invalid PTEs. This patch swaps the PTE_FILE and
PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge
PTEs.I guess we'll never get a huge_(pte|pmd)_file() (but we can shift the file bits up anyway).
Signed-off-by: Steve Capper <redacted>
Apart from the comments you already got: Acked-by: Catalin Marinas <catalin.marinas@arm.com>