There exists a four line chunk of code, which when configured for
64 bit address space, can incorrectly set certain page flags during
the TLB creation. It turns out that this is code which isn't used,
but might still serve a purpose. Since it isn't obvious why it exists
or why it causes problems, the below description covers both in detail.
For powerpc bootstrap, the physical memory (at most 768M), is mapped
into the kernel space via the following path:
MMU_init()
|
+ adjust_total_lowmem()
|
+ map_mem_in_cams()
|
+ settlbcam(i, virt, phys, cam_sz, PAGE_KERNEL_X, 0);
On settlbcam(), the kernel will create TLB entries according to the flag,
PAGE_KERNEL_X.
settlbcam()
{
...
TLBCAM[index].MAS1 = MAS1_VALID
| MAS1_IPROT | MAS1_TSIZE(tsize) | MAS1_TID(pid);
^
These entries cannot be invalidated by the
kernel since MAS1_IPROT is set on TLB property.
...
if (flags & _PAGE_USER) {
TLBCAM[index].MAS3 |= MAS3_UX | MAS3_UR;
TLBCAM[index].MAS3 |= ((flags & _PAGE_RW) ? MAS3_UW : 0);
}
For classic BookE (flags & _PAGE_USER) is 'zero' so it's fine.
But on boards like the the Freescale P4080, we want to support 36-bit
physical address on it. So the following options may be set:
CONFIG_FSL_BOOKE=y
CONFIG_PTE_64BIT=y
CONFIG_PHYS_64BIT=y
As a result, boards like the P4080 will introduce PTE format as Book3E.
As per the file: arch/powerpc/include/asm/pgtable-ppc32.h
* #elif defined(CONFIG_FSL_BOOKE) && defined(CONFIG_PTE_64BIT)
* #include <asm/pte-book3e.h>
So PAGE_KERNEL_X is __pgprot(_PAGE_BASE | _PAGE_KERNEL_RWX) and the
book3E version of _PAGE_KERNEL_RWX is defined with:
(_PAGE_BAP_SW | _PAGE_BAP_SR | _PAGE_DIRTY | _PAGE_BAP_SX)
Note the _PAGE_BAP_SR, which is also defined in the book3E _PAGE_USER:
#define _PAGE_USER (_PAGE_BAP_UR | _PAGE_BAP_SR) /* Can be read */
So the possibility exists to wrongly assign the user MAS3_U<RWX> bits
to kernel (PAGE_KERNEL_X) address space via the following code fragment:
if (flags & _PAGE_USER) {
TLBCAM[index].MAS3 |= MAS3_UX | MAS3_UR;
TLBCAM[index].MAS3 |= ((flags & _PAGE_RW) ? MAS3_UW : 0);
}
Here is a dump of the TLB info from Simics with the above code present:
------
L2 TLB1
GT SSS UUU V I
Row Logical Physical SS TLPID TID WIMGE XWR XWR F P V
----- ----------------- ------------------- -- ----- ----- ----- --- --- - - -
0 c0000000-cfffffff 000000000-00fffffff 00 0 0 M XWR XWR 0 1 1
1 d0000000-dfffffff 010000000-01fffffff 00 0 0 M XWR XWR 0 1 1
2 e0000000-efffffff 020000000-02fffffff 00 0 0 M XWR XWR 0 1 1
Actually this conditional code was used for two legacy functions:
1: support KGDB to set break point.
KGDB already dropped this; now uses its core write to set break point.
2: io_block_mapping() to create TLB in segmentation size (not PAGE_SIZE)
for device IO space.
This use case is also removed from the latest PowerPC kernel.
However, there may still be a use case for it in the future, like
large user pages, so we can't remove it entirely. As an alternative,
we match on all bits of _PAGE_USER instead of just any bits, so the
case where just _PAGE_BAP_SR is set can't sneak through.
With this done, the TLB appears without U having XWR as below:
-------
L2 TLB1
GT SSS UUU V I
Row Logical Physical SS TLPID TID WIMGE XWR XWR F P V
----- ----------------- ------------------- -- ----- ----- ----- --- --- - - -
0 c0000000-cfffffff 000000000-00fffffff 00 0 0 M XWR 0 1 1
1 d0000000-dfffffff 010000000-01fffffff 00 0 0 M XWR 0 1 1
2 e0000000-efffffff 020000000-02fffffff 00 0 0 M XWR 0 1 1
Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
The test to check whether we have _PAGE_SPECIAL defined is broken,
since we always define it, just not always to a meaninful value :-)
That broke 8xx and 40x under some circumstances.
This fixes it by adding _PAGE_SPECIAL for both of these since they
had a free PTE bit, and removing the condition around advertising
it.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This is an attempt at cleaning up a bit the way we handle execute
permission on powerpc. _PAGE_HWEXEC is gone, _PAGE_EXEC is now only
defined by CPUs that can do something with it, and the myriad of
#ifdef's in the I$/D$ coherency code is reduced to 2 cases that
hopefully should cover everything.
The logic on BookE is a little bit different than what it was though
not by much. Since now, _PAGE_EXEC will be set by the generic code
for executable pages, we need to filter out if they are unclean and
recover it. However, I don't expect the code to be more bloated than
it already was in that area due to that change.
I could boast that this brings proper enforcing of per-page execute
permissions to all BookE and 40x but in fact, we've had that now for
some time as a side effect of my previous rework in that area (and
I didn't even know it :-) We would only enable execute permission if
the page was cache clean and we would only cache clean it if we took
and exec fault. Since we now enforce that the later only work if
VM_EXEC is part of the VMA flags, we de-fact already enforce per-page
execute permissions... Unless I missed something
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This adds the PTE and pgtable format definitions, along with changes
to the kernel memory map and other definitions related to implementing
support for 64-bit Book3E. This also shields some asm-offset bits that
are currently only relevant on 32-bit
We also move the definition of the "linux" page size constants to
the common mmu.h file and add a few sizes that are relevant to
embedded processors.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This fixes a problem reported by Sean MacLennan where loading any
module would cause an oops. We weren't marking the pages containing
the module text as having hardware execute permission, due to a bug
introduced in commit 8d1cf34e ("powerpc/mm: Tweak PTE bit combination
definitions"), hence trying to execute the module text caused an
exception on processors that support hardware execute permission.
This adds _PAGE_HWEXEC to the definitions of PAGE_KERNEL_X and
PAGE_KERNEL_ROX to fix this problem.
Reported-by: Sean MacLennan <smaclennan@pikatech.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Now that they are almost identical, we can merge some of the definitions
related to the PTE format into common files.
This creates a new pte-common.h which is included by both 32 and 64-bit
right after the CPU specific pte-*.h file, and which defines some
bits to "default" values if they haven't been defined already, and
then provides a generic definition of most of the bit combinations
based on these and exposed to the rest of the kernel.
I also moved to the common pgtable.h most of the "small" accessors to the
PTE bits and modification helpers (pte_mk*). The actual accessors remain
in their separate files.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
