For LPAE, we have the following means for encoding writable or dirty
ptes:
                              L_PTE_DIRTY       L_PTE_RDONLY
    !pte_dirty && !pte_write        0               1
    !pte_dirty && pte_write         0               1
    pte_dirty && !pte_write         1               1
    pte_dirty && pte_write          1               0

So we can't distinguish between writeable clean ptes and read only
ptes. This can cause problems with ptes being incorrectly flagged as
read only when they are writeable but not dirty.

This patch renumbers L_PTE_RDONLY from AP[2] to a software bit #58,
and adds additional logic to set AP[2] whenever the pte is read only
or not dirty. That way we can distinguish between clean writeable ptes
and read only ptes.

HugeTLB pages will use this new logic automatically.

We need to add some logic to Transparent HugePages to ensure that they
correctly interpret the revised pgprot permissions (L_PTE_RDONLY has
moved and no longer matches PMD_SECT_AP2). In the process of revising
THP, the names of the PMD software bits have been prefixed with L_ to
make them easier to distinguish from their hardware bit counterparts.
Signed-off-by: NSteve Capper <steve.capper@linaro.org>
Reviewed-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

On non-LPAE ARMv6+, read-only PMD bits are defined with the combination
"PMD_SECT_APX | PMD_SECT_AP_WRITE". Adjusted the bit masks to correctly
report this.
Signed-off-by: NKees Cook <keescook@chromium.org>
Tested-by: NLaura Abbott <lauraa@codeaurora.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

On 2-level page table systems, the PMD has 2 section entries. Report
these, otherwise ARM_PTDUMP will miss reporting permission changes on
odd section boundaries.
Signed-off-by: NKees Cook <keescook@chromium.org>
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Tested-by: NSteve Capper <steve.capper@linaro.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

This patch allows the kernel page tables to be dumped via a debugfs file,
allowing kernel developers to check the layout of the kernel page tables
and the verify the various permissions and type settings.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>